Rozprawy doktorskie na temat „Cemented”

This master thesis work aims towards gaining a deeper understanding of residualstresses in cemented carbide rock drill inserts. Compressive stresses are wanted inthe surface material since they prevent crack growth and wear of the material andthis work is part of the development of better and longer lasting inserts.Different ways of measuring residual stress with 2-dimensional x-ray diffraction areinvestigated. Also different surface treatment methods, used for attaining thesecompressive stresses, are tested and evaluated by measuring surface residual stress.Also hardness and residual stress in-depth profiles are measured by cutting treatedinserts in half and perform measurement on cross sections.The results show that measurements can be conducted on the raw sample surfacewith a 0.5 mm x-ray spot size. The effectiveness of surface treatments varies withdifferent cemented carbide grades. Blasting gives rise to the highest compressivestresses in a harder cemented carbide grade while it produces a lot of crushedtungsten carbide grains and similar stresses as tumbling in a softer grade. Treatment Tgives interesting result since it produces high compressive stress but still leaves thesurface grains unbroken. Attempts to measure both hardness and residual stressgradients from the surface are found to be difficult. Large effects from samplepreparation and deviations in measured data give uncertain results but tumbling seemsto affect the material deeper down from the surface compared to both blasting andtreatment T. This is also confirmed by a larger increase of coercive field strength intumbled samples.

Mining has been one of the main industries in the course of the development of human civilization and economies of various nations. However, every industry has issues, and one of the problems the mining industry has faced is the management of waste, especially sulphide-bearing tailings, which are considered to be a global environmental problem. This issue puts pressure on the mining industry to seek alternative approaches for tailings management. Among the several different types of methods used, cemented paste backfilling is one of the technologies that offers good management practices for the disposal of tailings in underground mines worldwide. Cemented paste backfill (CPB) is a cementitious composite made from a mixture of mine tailings, water and binder. This technology offers several advantages, such as improving the production and safety conditions of underground mines. Among these advantages, CPB is a promising solution for the management of sulphidic tailings, which are considered to be reactive materials (i.e., not chemically stable in an atmospheric condition) and the main source of acid mine drainage, which constitutes a serious environmental challenge faced by mining companies worldwide. Such tailings, if they come into direct contact with atmospheric elements (mainly oxygen and water), face oxidation of their sulphidic minerals, thus causing the release of acidic drainage (i.e., acid mine drainage) and several types of heavy metals into surrounding water bodies and land. Therefore, the reactivity of sulphidic tailings with and without cement content can be considered as a key indicator of the environmental behavior and durability performance of CPB systems. For a better understanding of the reactivity, it is important to investigate the influencing factors. In this research, several influencing factors are experimentally studied by conducting oxygen consumption tests on different sulphidic CPB mixtures as well as their tailings under different operational and environmental conditions. These factors include time, curing temperature, initial sulphate content, curing stress, mechanical damage, binder type and content, and the addition of mineral admixtures. In addition, several microstructural techniques (e.g., x-ray diffraction and scanning electron microscopy) are applied in order to understand the changes in the CPB matrices and identify newly formed products. The results reveal that the reactivity of CPB is affected by several factors (e.g., curing time, initial sulphate content, ageing, curing and atmospheric temperature, binder type and content, vertical curing stress, filling strategy, hydration and drainage, etc.), either alone or in combination. These factors can affect reactivity either positively or negatively. It is observed that CPB reactivity decreases with increasing curing time, temperature (i.e., curing and atmospheric temperatures), curing stress, binder content, the addition of mineral admixtures, degree of saturation, and the binder hydration process, whereas reactivity increases with increases in sulphide minerals (e.g., pyrite), initial sulphate content, mechanical damage, and with decreased degrees of saturation and binder content. The effect of sulphate on the reactivity of CPB is based on the initial sulphate content as well as curing time and temperature. It is concluded that the reactivity of CPB systems is time- and temperature-dependent with respect to other factors. Also, binders play a significant role in lowering CPB reactivity due to their respective hydration processes.

With the aim to achieve a better understanding of the time-dependent behaviour of structured clays, especially cemented clay, a critical review of the literature and a programme of laboratory testing have been carried out. In order to investigate the time effects on different structured clays, a series of advanced triaxial and oedometer tests were conducted on reconstituted pure kaolin (PK), artificially cemented kaolin (ACK) with different curing periods, and remoulded artificially cemented kaolin (RACK). Strain rate effects were examined in pure kaolin with different degrees of over-consolidation in both undrained and drained shearing. The influence of bond structure on the monotonic stress-strain behaviour of cemented kaolin was investigated on specimens prepared with two different curing stress and curing periods. Tests on pure kaolin and remoulded cemented kaolin were also performed. Strain rate effects on long cured cemented kaolin under low and high confining stresses, with constant rate of straining in pre-peak stage and step-wise change rate of straining in post-peak stage were examined. This was completed by a study of the microstructure of pure kaolin and cemented kaolin specimens before and after tests via scanning electronic microscope. The coupling between stress or strain rate and curing time effects was investigated on cemented kaolin cured for shorter periods. The results have added significant data to the existing database and addressed the relationship between bond structure and time effect. The main conclusions are: ••The viscous type of PK determined is characterized as decaying positive isotache and General TESRA in undrained and drained shearing repectively. The strain rate history does not affect the critical state in both q-p’ and v-ln p’ spaces. ••The addition of cement not only creates new inter-particle bonds but also affects new fabric. The shear strength is dominated by bond structure under low confining stress, and by volume change under high confining stress. ••The viscous type of long-term cured ACK is dependent on the degree of bond structure. It is almost insensitive to strain rate changes when the specimen is stiff, and the apparent “aging” effect dominates resulting in a “negative” rate effect when bond structure is destroyed. A special rate phenomenon called stick-slip seems to occur under the lowest strain rate (0.01%/h) during the pre-peak stage. The RACK shows a TESRA type of viscosity in undrained shearing. ••The short-term cured ACK, in which structuring and rate effects are combined, shows negative rate effects due to the curing under low confining stress and apparent aging under high confining stress. Stick-slip occurs both in pre-peak and post-peak stages, due to different reasons.
published_or_final_version
Civil Engineering
Doctoral
Doctor of Philosophy

The lasting integrity of the bond between bone cement and bone defines the long-term stability of cemented acetabular replacements. Although several studies have been carried out on bone-cement interface at continuum level, micromechanics of the interface has been studied only recently for tensile and shear loading cases. Furthermore, the mechanical and microstructural behaviour of this interface is complex due to the variation in morphology and properties that can arise from a range of factors. In this work in vitro studies of the bone-cement interfacial behaviour under selected loading conditions were carried out using a range of experimental techniques. Damage development in cemented acetabular reconstructs was studied under a combined physiological loading block representative of routine activities in a saline environment. A custom-made environmental chamber was developed to allow testing of acetabular reconstructs in a wet condition for the first time and damage was monitored and detected by scanning at selected loading intervals using micro-focus computed tomography (μCT). Preliminary results showed that, as in dry cases, debonding at the bone-cement interface defined the failure of the cement fixation. However, the combination of mechanical loading and saline environment seems to affect the damage initiation site, drastically reducing the survival lives of the reconstructs. Interfacial behaviour of the bone-cement interface was studied under tensile, shear and mixed-mode loading conditions. Bone-cement coupons were first mechanically tested and then μCT imaged. The influence of the loading angle, the extent of the cement penetration and the failure mechanisms with regard to the loading mode on the interfacial behaviour were examined. Both mechanical testing and post failure morphologies seem to suggest an effect of the loading angle on the failure mechanism of the interface. The micromechanical performance of bone-cement interface under compression was also examined. The samples were tested in step-wise compression using a custom-made micromechanical loading stage within the μCT chamber, and the damage evolution with load was monitored. Results showed that load transfer in bone-cement interface occurred mainly in the bone-cement contact region, resulting in progressively developed deformation due to trabeculae bending and buckling. Compressive and fatigue behaviour of bovine cancellous bone and selected open-cell metallic foams were studied also, and their suitability as bone analogous materials for cemented biomechanical testing was investigated. Whilst the morphological parameters of the foams and the bone appear to be closer, the mechanical properties vary significantly between the foams and the bone. However, despite the apparent differences in their respective properties, the general deformation behaviour is similar across the bone and the foams. Multi-step fatigue tests were carried out to study the deformation behaviour under increasing compressive cyclic stresses. Optical and scanning electron microscopy (SEM) were used to characterise the microstructure of foams and bone prior to and post mechanical testing. The results showed that residual strain accumulation is the predominant driving force leading to failure of foams and bones. Although foams and bone fail by the same mechanism of cyclic creep, the deformation behaviour at the transient region of each step was different for both materials. Preliminary results of foam-cement interface performance under mixed-mode loading conditions are also presented.

Cemented rockfill, CRF, is comprised of sized aggregate mixed with various types and amounts of binder materials. This type of fill with closely controlled specifications is employed for subsequent pillar recovery and improved ground support.
The goal of this study is to improve consolidated rockfill design for bulk mining methods, with Kidd Creek Mines, KCM, as a case study, from a functional and cost point of views. Cemented rockfill at KCM represents approximately 20% of the total extraction costs. Cost cutting initiatives however have to be mindful of the negative if not disastrous effects on grade, recovery, and ground stability that a decline in fill quality can produce. This dictates that any attempt to cut operational costs should be approached in a scientific and orderly fashion. This thesis describes consolidated rockfill improvement steps taken at Kidd Creek to obtain the highest quality fill at the lowest possible cost.
The main trust and achievements in this thesis include: (1) Extensive site investigation and mapping in drift driven through backfill have resulted establishment of four distinct zones in a typical rockfill mass. Structural rockfill design steps using the information obtained from field mapping are then established and implemented at KCM with great success which will be described during this thesis. (2) The main body of this thesis contains significant amounts of laboratory test work, 1750 test specimen, on lower cost binder alternatives. Some of the results obtained from the test work have been implemented at Kidd Creek since late 1992 and have resulted in considerable savings and improved dilution control. (3) Quality control measures and techniques in three main stages, surface plant, during transportation, and most importantly during placement are also established. (4) CRF structural design optimization steps are identified through extensive site observation and consultation with other operations. This covers all the steps that should be taken from start to finish to achieve the highest quality rockfill at the lowest possible cost. (5) Extensive field experiments are also carried out to obtain in situ mechanical and dynamical properties of a typical rockfill mass.
This work is based upon field and laboratory studies undertaken within the KCM over a 5 year period. The work has resulted in establishing quality control measures, mix design improvement, and structural design implementation at KCM to achieve the required physical characteristics at the lower operational cost. The in situ and laboratory test resulted in 35% unit cost reduction for KCM rockfill system within last 3 years and a saving of around $4 million on binder cost alone at a rate of $1.3 million/year. The total unit cost has dropped from $12/tonne in 1991 to around $7/tonne in 1995.

WC cemented carbides are composites consisting of WC and a binder phase. WC/Co is widely used as cutting tools due to its excellent combination of hardness and toughness. This thesis work was performed at the R&D department of Sandvik Coromant and aimed to find the alternative binder phase to substitute cobalt. Several compositions of Fe-Ni and Fe-Ni-Co binder have been investigated in this study. The WC/Co reference samples were also prepared. The initial compositions were decided by the CALPHAD method. The samples were then produced by the means of powder metallurgy. The producing conditions, especially the sintering conditions, were manipulated to achieve full dense and uniform samples. The samples were analyzed by XRD, LOM, SEM, and EDS. Mechanical properties test has also been performed.The results showed that adjustment on carbon content is necessary to attain desirable structure. Increasing Fe content in the binder tends to make the materials harder. For Fe-Ni and Fe-Ni-Co, the martensitic transformation is essential to the mechanical performance. The induced “transformation toughening” in 72Fe28Ni and 82Fe18Ni binders significantly promoted the toughness. Furthermore, the grain growth inhibition by Fe was confirmed. The relations between sintering temperature, grain size and mechanical properties have been discussed. Compared with the WC/Co references, several compositions showed close and even superior mechanical performance which might provide solutions for the future alternative binder phase.

In view of the extensive use of Cr as a grain growth inhibitor in WC-Co cemented carbides this thesis comprises a combined experimental and ab initio study of a number of critical issues pertaining to phase equilibria of the subsystems to the W-Co-Cr-C system. To be able to predict which of the stable Cr-carbides forms above the solubility limits of Cr and C in the fcc phase the respective solubility of Co in Cr23C6, Cr7C3 and Cr3C2 are investigated experimentally. Furthermore, the site occupancies of Co in Cr7C3 are investigated by neutron diffraction as a first step towards a more realistic model for this phase. The energetics of the ternary intermetallic R-phase and the unstable Co3C2 end-member compound are investigated by density functional theory. For Co3C2, the quasi-harmonic vibrational Gibbs energy is also calculated. By subsequent CALPHAD assessment an improved thermodynamic description is developed and its agreement with experiment is investigated. The resulting thermodynamic description allows for improved accuracy in predicting the formation of carbide phases as a function of C content and Co/Cr ratio as well as liquidus and solidus temperatures. Remaining issues may be attributed to the thermodynamic description of the W-Cr-C system and the stability of the Cr-based carbides in the Cr-C system. In the case of the Cr-based carbides, severe experimental scatter prevents an accurate determination of the stability of either of them. As a first attempt to resolve the situation, a state of the art ab initio approach is applied to calculate the finite temperature thermodynamic properties of Cr3C2, benchmarked with reported heat capacity and relative thermal expansion measurements.

QC 20151029

Cemented carbides are used in a multitude of applications within machining as they can withstand tough conditions. Therefore, the stress state in a virgin material is of interest. After cooling from the sintering stage during cemented carbide production, the large difference in coefficients of thermal expansion of the constituents results in thermal residual microstresses. These may be of significant magnitude that could influence the material's performance in later applications. The present work is therefore concerned with these thermal residual microstresses and deals with them through 2D finite element calculations in ANSYS APDL. The geometry was chosen to try to emulate different conditions that could happen within a cemented carbide grain. The tungsten phase was modeled as fully elastic and the cobalt phase as elastic-plastic with linear hardening. The results show that the stress levels reach such magnitudes that the simple material models used in this work, as well as in previous works, are not sufficient to accurately capture the behavior of the material. The stress levels far exceed the strength of the materials, which would cause them to fail. However, that is not the case in reality. Further, the simulations showed that the microgeometry plays a large role in the distribution of the stresses within each phase. In general, the cobalt phase is subjected to tension and the tungsten phase to compression. However, under certain conditions parts of the tungsten phase can also show tensile stresses.
Hårdmetaller används i många tillämpningar inom skärande bearbetning på grund av dess egenskaper. De klarar av de stora belastningar som uppstår under kontakter i processerna. På grund av obesvarade frågor när det gäller till exempel sprickbildning är spänningstillståndet i ett obelastat material av intresse. Under tillverkningen av hårdmetaller, måste kompositen kylas ned efter sintringen. Kobolt och wolframkarbid har mycket olika värmeutvidgningskoefficienter, vilket resulterar i att termiska restspänningar uppstår. Dessa kan nå en betydande storlek vilket kan påverka materialets prestation under senare användning.  Detta arbete behandlar dessa termiska restspänningar genom finita elementberäkningar i ANSYS APDL. Geometrin gjordes i 2D, och valdes för att försöka efterlikna de förhållanden som kan råda inuti ett korn av hårdmetall. Wolframkarbiden modellerades som helt elastisk medan kobolten modellerades som elastisk-plastisk med linjärt hårdnande.  Resultaten visar att spänningsnivåerna når sådana nivåer att materialet inte borde klara av belastningen. Materialmodellerna i detta arbete, och tidigare arbeten, är för enkla för att korrekt beskriva materialens beteende. Spänningsnivåerna överstiger materialets styrka, vilket skulle orsaka brott. Detta överensstämmer inte med verkligheten. Vidare visar simuleringarna att mikrogeometrin har spelar stor roll för spänningsfördelningen inom varje fas, där det kan vara stor skillnad inom samma fas. Generellt sett, hamnar kobolten i ett dragtillstånd och wolframkarbiden i tryck. Det finns dock vissa förutsättningar som leder till dragspänningar inom vissa delar av wolframkarbiden.

The aim of the present work is to study the formation of the cubic carbide phase (gamma phase) free gradient zone and the gamma cone structure at the edges of gradient sintered cemented carbides. Four types of cemented carbides; WCTi(C,N)-Co, WC-Ti(C,N)-Ni, WC-Ti(C,N)-Fe, WC-(Ti,Ta,NB)(C,N)-Co were gradient sintered and the thicknesses of the gradients were measured. Formation of the gradients is simulated and the simulations results are compared with experimental data. For all of the one-dimensional simulations, the DICTRA [1] software is used. The two-dimensional simulations are carried out by using a new simulation tool which is called “YAPFI”. The YAPFI software is a tool for simulation of diffffusion in multiphase systems along one, two, or three spatial coordinates. Various numerical parameters have been studied by running less computationally demanding one-dimensional simulations. The optimized parameters are used to setup the two-dimensional simulations. Two different kinetic databases were used in the simulations. The effect of different so-called labyrinth factors were studied systematically. The simulation results are in close agreement with the experimental observations, although some anomalies are present in the results. Results of the two-dimensional simulations show the formation of the gamma cone at the edges of the insert.

The behavior of cemented sands is examined experimentally and theoretically in this study. The first segment of the investigation involves an extensive laboratory program to examine the effects of slenderness ratio, effects of cementation, and effects of confining pressure on the stress-strain curves of cemented sands. Results show that specimens with slenderness ratio of 1.5 or greater exhibit lower strength, higher dilatation rates, and relatively brittle behavior when compared to samples with slenderness ratio of 1. Furthermore, cemented sands have an essentially straight line Mohr-Coulomb failure envelope, whose cohesion intercept increases with the degree of cementation of the soil. The effective friction angles measured for cemented sands with various cementation levels are in the same ranges as the effective friction angle evaluated for uncemented sands. Moreover, failure modes of the material varies from brittle to ductile depending upon the level of cementation and the degree of confinement. In general, as cementation increases, cemented sand exhibits a brittle failure behavior; while increasing the confining pressure causes a ductile failure response. The second portion of the project includes development of a constitutive model for cemented sands. Cemented sand is viewed as a multi-phase material comprising three phases: sand, cement, and pore water. The elastoplastic behavior of cemented sands is the consequence of the behavior of the individual phases plus the interaction of the phases. The individual phases (sand and cement) are modeled using the theory of plasticity. Mixtures theory is used to assemble the individual phases to simulate the overall behavior of cemented sands. The gradual damage of the internal structure of cemented sands is also incorporated within the model. The agreement between experimental data and model predictions is very good. In summary, mixtures theory using simple plasticity models for the individual phases is capable of capturing the complex behavior of cemented sands.

Cemented carbides based on tungsten carbide and cobalt arecommonly produced by a powder metallurgy route including liquidphase sintering. The pressed compact densifies to almost halfits volume during sintering due to pore elimination. Thesintering behaviour changes with material composition, such ascarbide grain size, binder fraction, carbon content andaddition of cubic carbides.

This thesis is devoted to the study of constitutivebehaviour, in particular densification, and the microstructuralevolution during cemented carbide sintering. Dimensionalchanges are monitored using dilatometry with and withoutapplied external load. The microstructural evolution isinvestigated with light optical microscopy and scanningelectron microscopy. Thermodynamic calculations are used asreference.

Constitutive relations are derived for uniaxial viscosity,viscous equivalent of Poisson’s ratio and sintering stressbased on relative density and temperature. The relations areextended to a model describing sintering shrinkage withexplicit dependencies on carbide grain size and binder content.The model is divided in three stages of which two pertain tothe solid state and the third to liquid phase sintering. Solidstate shrinkage is suppressed in a material with coarsecarbides and in the stage of liquid phase sintering grain sizestrongly influences the uniaxial viscosity. The binder contentaffects primarily the later densification.

The effects of carbon content and grain size distribution onshrinkage have been studied. High carbon content enhancesshrinkage rate, but the effect of grain size distribution israther small. The mean carbide grain size is insufficient todescribe densification for very broad distributions only.

Shrinkage occurs through rearrangement andsolution-reprecipitation. Rearrangement is studied through theevolution of the pore size distribution and simulatedgenerically using a discrete element method.

Keywords:Cemented carbides, Sintering, Constitutiverelations, Microstructure, Densification, Modelling

Cabonate-hosted hydrocarbon reservoirs will play an increasingly important role in the energy supply, as 60% of the world's remaining hydrocarbon resources are trapped within carbonate rocks. The properties of carbonates are controlled by deposition and diagenesis, which includes calcite cementation that begins immediately after deposition and may have a strong impact on subsequent diagenetic pathways. This thesis aims to understand the impact of early calcite cementation on reservoir properties through object-based modelling and Lattice Boltzmann ow simulation to obtain permeability. A Bayesian inference framework is also developed to quantify the ability of Lattice Boltzmann method to predict the permeability of porous media. Modelling focuses on the impact of carbonate grain type on properties of early cemented grainstones and on the examination of the theoretical changes to the morphology of the pore space. For that purpose process-based models of early cementation are developed in both 2D (Calcite2D) and 3D (Calcite3D, which also includes modelling of deposition). Both models assume the existence of two grain types: polycrystalline and monocrystalline, and two early calcite cement types specific to these grain types: isopachous and syntaxial, respectively. Of the many possible crystal forms that syntaxial cement can take, this thesis focuses on two common rhombohedral forms: a blocky form 01¯12 and an elongated form 40¯41. The results of the 2D and 3D modelling demonstrate the effect of competition of growing grains for the available pore space: the more monocrystalline grains present in the sample, the stronger this competition becomes and the lesser the impact of each individual grain on the resulting early calcite cement volume and porosity. The synthetic samples with syntaxial cements grown of the more elongated crystal form 40¯41 have lower porosity for the same monocrystalline grains content than synthetic samples grown following more blocky crystal form 01¯12. Moreover, permeability at a constant porosity is reduced for synthetic samples with the form 40¯41. Additionally, synthetic samples with form 40¯41 exhibit greater variability in the results as this rhombohedral form is more elongated and has the potential for producing a greater volume of cement. The results of the 2D study suggest that for samples at constant porosity the higher the proportion of monocrystalline grains are in the sample, the higher the permeability. The 3D study suggests that for samples with crystal form 01¯12 at constant porosity the permeability becomes lower as the proportion of monocrystalline grains increase, but this impact is relatively minor. In the case of samples with crystal form 40¯41 the results are inconclusive. This dependence of permeability on monocrystalline grains is weaker than in the 2D study, which is most probably a result of the bias of flow simulation in the 2D as well as of the treatment of the porous medium before the cement growth model is applied. The range of the permeability results in the 2D modelling may be artificially overly wide, which could lead to the dependence of permeability on sediment type being exaggerated. Poroperm results of the 2D modelling (10-8000mD) are in reasonable agreement with the data reported for grainstones in literature (0.1-5000mD) as well as for the plug data of the samples used in modelling (porosity 22 - 27%, permeability 200 - 3000mD), however permeability results at any given porosity have a wide range due to the bias inherent to the 2D flow modelling. Poroperm results in the 3D modelling (10 - 30, 000mD) exhibit permeabilities above the range of that reported in the literature or the plug data, but the reason for that is that the initial synthetic sediment deposit has very high permeability (58, 900mD). However, the trend in poroperm closely resembles those reported in carbonate rocks. As the modelling depends heavily on the use of Lattice Boltzmann method (flow simulation to obtain permeability results), a Bayesian inference framework is presented to quantify the predictive power of Lattice Boltzmann models. This calibration methodology is presented on the example of Fontainebleau sandstone. The framework enables a systematic parameter estimation of Lattice Boltzmann model parameters (in the scope of this work, the relaxation parameter τ ), for the currently used calibrations of Lattice Boltzmann based on Hagen-Poiseuille law. Our prediction of permeability using the Hagen-Poiseuille calibration suggests that this method for calibration is not optimal and in fact leads to substantial discrepancies with experimental measurements, especially for highly porous complex media such as carbonates. We proceed to recalibrate the Lattice Boltzmann model using permeability data from porous media, which results in a substantially different value of the optimal τ parameter than those used previously (0.654 here compared to 0.9). We augment our model introducing porosity-dependence, where we find that the optimal value for τ decreases for samples of higher porosity. In this new semi-empirical model one first identifies the porosity of the given medium, and on that basis chooses an appropriate Lattice Boltzmann relaxation parameter. These two approaches result in permeability predictions much closer to the experimental permeability data, with the porosity-dependent case being the better of the two. Validation of this calibration method with independent samples of the same rock type yields permeability predictions that fall close to the experimental data, and again the porosity-dependent model provides better results. We thus conclude that our calibration model is a powerful tool for accurate prediction of complex porous media permeability.

An experimental investigation was conducted on the static liquefaction behaviour of very loose lightly cemented sands. Undrained and drained triaxial compression tests, one dimensional consolidation, high stress compression, and unconfined compression tests were performed on artificially prepared lightly cemented loose samples with cement-sand ratios of 2, 4 and 6%. Additional tests were also conducted on uncemented samples prepared at the same initial void ratio as the cemented samples. Besides the influence of degree of cementation, the effects of void ratio and confining pressure on the liquefaction potential of cemented sands were examined. The aim of this study is to make significant contribution to the understanding of static liquefaction failures in lightly cemented sands. It is shown that cementation could increase the initial stiffness and yield strength of cemented sands but its effect might decrease considerably after the peak strength because of destruction of the cementation bond. The response of cemented sands at lower cement contents was very similar to the response of loose sands and behaviour approached the response of medium to dense sands with increase in the degree of cementation. It is also shown that degree of cementation has a significant influence on liquefaction resistance. Even though the presence of small amounts of cementation did not prevent liquefaction failure, the liquefaction resistance of cemented sands generally increased for higher degrees of cementation. The consolidation, high stress compression and unconfined compression tests demonstrated the effect of cementation in increasing both the stiffness and strength of cemented sands. The unconfined compression strength increased approximately linearly with the increase in cement content. The rate of strength gain increased with an increase in the dry density of the compacted sample, indicating that the cementation was more for denser samples.

The behaviour of natural soils is highly influenced by structural features arising from their geological history and was recognised to lie outside current frameworks which account only for the stress-volume state of the soil. The objective of the research was to compare the shear behaviour and stiffness of two naturally cemented sands: a calcarenite with relatively low densities, weak particles and strong bonding and a silica sandstone with high densities, strong particles and weak bonding. Comparative studies were also undertaken on their corresponding reconstituted soils and on an artificially cemented carbonate sand. Testing was performed in stress path controlled triaxial systems over a wide range of confining pressures. Identification of the yield surface was found to be an essential feature to describe the shear behaviour of the soils examined. The determination of the yield points of such stiff soils required internal measurements of stresses and strains, with an accuracy higher than currently achieved in soil testing. For reliable determinations of stiffness and yielding the uniformity of strains in the samples had to be guaranteed. Therefore several parts of the equipment were redesigned or modified and new sample preparation and setting up procedures were developed. Comparison of results from natural and reconstituted soils showed that bonding increased the stiffness and the stress-strain linearity. For the naturally cemented sands the maximum shear modulus was found to vary with state only when the soils were sheared after isotropic yielding. Undrained loading-unloading probes showed that the linear behaviour was reversible and that plastic strains were accompanied by a progressive deterioration of bonding resulting initially in a reduction of the yield stresses and finally, after sufficient cycling in a decrease of the maximum shear modulus. The combined influence of bond strength and specific volume on yielding could be accounted for when normalizing the yield stresses by an equivalent pressure taken on the state boundary in isotropic compression. This type of normalization also allowed the full state boundary to be identified. The yield surface was found to be the boundary limiting the domain governed by bonding and for the calcarenite occupied a larger portion of the permissible states than for the silica sandstone. States between the yield surface and the state boundary surface were controlled by bond degradation and either particle crushing for the calcarenite or dilation for the silica sandstone. After accounting for differences in states, both naturally cemented sands showed peak strengths which were higher than those for the reconstituted soils. For the calcarenite the peak strengths simply resulted from cohesion, as the peak stress ratios were reached on the yield surface. Only when stress ratios at yielding were lower than the critical state stress ratio the strength was truly frictional and coincident with the critical state. For the silica sandstone, in contrast, the peak strengths were found to be frictional except at the lowest confining pressures. The peak stress ratios were reached at states above the yield surface and were associated with a maximum rate of dilation. The dilatancy and strength of the intact soil were higher than those of the reconstituted soil at comparable states and were interpreted as resulting from differences in fabric and from the delayed volumetric response induced by the presence of bonding at the early stages of shearing. The case of the silica sandstone showed that only when density is a predominant factor in comparison with bonding then different modes of shear behaviour follow the theory of Critical State Soil Mechanics.

As implant survival extends into the second and third decades focal osteolysis around cemented femoral components in total hip replacement is emerging as an important failure mechanism. Whilst the problem of focal osteolysis is well recognised, there are many aspects of its development which are poorly understood. The broad aim of this thesis is to try to provide some insights into how, why and where focal osteolysis develops around the cemented femoral component. There are broadly two sections to this thesis, chapters 2-5 present clinical and geometrical studies and chapters 6-10 a series of experimental studies. The aim of the first section was to establish what is observed in clinical practice, the aim of the second to try to explain these findings. A mid-term clinical study showed that focal osteolysis is more common with rough than polished stems that differed in no aspect other than their surface finish. Further studies established that focal osteolysis is probably always associated with defects in the cement mantle. These defects occur anteriorly at the mid-stem of the prosthesis and posteriorly at the component tip. The distribution of focal osteolysis and its strong association with cement mantle defects suggests the importance of the stemcement interface as a pathway for fluid and debris to reach the distal femur. However, at 15-25 years, osteolysis rarely develops with the polished Exeter stem even in the presence of confirmed defects in the cement mantle, suggesting that the stem seals the stem-cement interface against fluid and debris. In an attempt to explain the clinical findings a series of bench top experiments were undertaken. These studies showed that the behaviour of fluid and dye at the stemcement interface was significantly influenced by component surface finish. Bonded and debonded stem-cement interfaces of rough stems provided an incomplete barrier to fluid movement along this interface. In contrast, polished stems both bonded and debonded were able to provide a seal at the stem-cement interface. The seal at this interface was improved with component subsidence in the presence of rotational stability. It is believed that this thesis provides a rationale explanation for why focal osteolysis rarely develops around the Exeter stem in clinical practice. It also explains how, where, and why osteolysis develops around certain designs of cemented femoral components used in total hip replacement.

The usage of cobalt (Co) as binder phase material in cemented carbides has been questioned becauseof the potential health hazards associated with cobalt particle inhalation. Cobalt is used because ofits excellent adhesive and wetting properties, combined with adequate mechanical properties. Thepurpose of this work is to investigate the mechanical properties of Fe-Ni bulk alloys and WC-Cocemented carbides using Integrated Computational Materials Engineering (ICME) methods com-bined with FEM data. The report investigates the mechanical properties of several bulk alloys inthe Fe-Ni system as a function of void size and fraction. FEM indentation and FEM fracture datais interpolated and used to model the hardnessHand fracture toughnessKIc. A precipitationhardening model based on the Ashby-Orowan’s equation is implemented to predict the e↵ect on theyield strength from precipitated particles. A model for solid solution hardening is also implemented.Existing models are used to simulate the properties of WC-Co cemented carbides together with thesolid solution hardening model. Results show that the simulated properties of the Fe-Ni bulk alloysare comparable to those of cobalt. However, the results could not be confirmed due to a lack ofexperimental data. The properties of WC-Co cemented carbides are in reasonable agreement withexisting experimental data, with an average deviation of the hardness by 11.5% and of the fracturetoughness by 24.8%. The conclusions are that experimental data for di↵erent Fe-Ni bulk alloys isneeded to verify the presented models and that it is possible to accurately model the properties ofcemented carbides.
Anv¨andandet av kobolt (Co) som bindefas-material i h°ardmetall har blivit ifr°agasatt som en f¨oljdav av de potentiella h¨alsoriskerna associerade med inhalering av koboltpartiklar. Kobolt anv¨ands p°agrund av dess utm¨arkta vidh¨aftande och v¨atande egenskaper, kombinerat med tillr¨ackliga mekaniskaegenskaper. Syftet med detta arbete ¨ar att unders¨oka de mekaniska egenskaperna hos Fe-Ni bulklegeringarochWC-Co h°ardmetall genom att anv¨anda Integrated Computational Materials Engineering(ICME) metoder kombinerat med FEM-data. Rapporten unders¨oker de mekaniska egenskapernahos flera bulklegeringar i Fe-Ni systemet. FEM-indentering och FEM-fraktur data interpoleras ochanv¨ands f¨or att modellera h°ardheten H och brottsegheten KIc. En modell f¨or utskiljningsh¨ardningbaserad p°a Ashby-Orowans ekvation implementeras f¨or att f¨oruts¨aga e↵ekten p°a brottgr¨ansen av utskiljdapartiklar. ¨Aven en modell f¨or l¨osningsh¨ardning implementeras. Existerande modeller anv¨andsf¨or att simulera egenskaperna hos WC-Co h°ardmetall tillsammans med modellen f¨or l¨osningsh¨ardning.Resultaten visar att de simulerade egenskaperna hos Fe-Ni bulklegeringar ¨ar j¨amf¨orbara medde f¨or kobolt. Dock kan de inte bekr¨aftas p°a grund av avsaknad av experimentell data. Egenskapernahos WC-Co h°ardmetall st¨ammer rimligt ¨overens med existerande experimentell data, meden genomsnittlig avvikelse av h°ardheten med 11.5% och av brottsegheten med 24.8%. Slutsatserna¨ar att det beh¨ovs experimentell data f¨or Fe-Ni bulklegeringar f¨or att kunna verifiera modellernasnoggrannhet och att det ¨ar m¨ojligt att f¨oruts¨aga egenskaperna hos h°ardmetall.

In this Master Thesis work, the effect of pressure on sintering of cemented carbides is investigated. Special focus hasbeen given to the residual porosity after sintering. It is well known that sintering shrinkage depends on binder phasecontent, grain size, temperature and pressure. Thus 4 different cemented carbides grades were selected. The gradeswere pressed into standard products and TRS (Tensile Rupture Strength) rods with two different shrinkage factors.These were then sintered at different pressures and temperatures. Thereafter the impact of pressure on propertiessuch as Density, Coercivity, Porosity and TRS were analyzed. The observations were further supported with Weibullprobability analysis and fracture surface analysis in SEM.It has been shown that there exists a distinct threshold pressure at which significant reduction in porosity occurs forgiven compacted densities. For 3 out of 4 cemented carbide grades it has been observed that P2 sintering pressure issufficient to meet desired product characteristics. The fourth grade required a minimum sintering pressure of P4 toachieve desired quality criteria. Moreover it has been concluded that an increased sintering pressure increasesmaterial strength, as compared to vacuum sintering, thereby reducing the amount of early failures caused by poresduring TRS test.                                    Keywords: Cemented Carbides, Pressurized Sintering, Tungsten carbide, Porosity, Vacuum sintering, TensileRupture Strength, Weibull analysis, Fracture surface analysis.

The principle scope of this research was to develop relationship between stope dimensions and cemented paste fill strength. Experiments in various fill thickness to span width ratios with cemented paste fill with different mechanical properties were conducted by using a constructed scaled-down open stope. Scaled-down laboratory experiments were used to understand the mechanism of fill failure when exposure is undertaken under a relatively fresh fill mass.

Cemented Granular Materials (CGMs) are ubiquitous in nature. Their behaviour is driven by phenomena occurring at the scale of individual grains and cement bonds. However, the effect of this scale on the engineering response has lacked a systematic description and is rarely acknowledged in the models portraying their behaviour. This dissertation contributes to the development of a methodological framework for CGMs, relating the behaviour of individual grains to their collective response at the macroscopic scale, through a combination of analytical, experimental and numerical approaches. Analytically, a novel constitutive model for CGMs is developed, which adopts measurable internal variables describing the evolution of key grain-scale processes. This model can successfully predict stress-strain responses as well as the onset and development of localisation patterns for a wide range of pressure regimes. Its constitutive parameters have a precise physical meaning and are directly quantifiable. Experimentally, a triaxial testing program is carried out on specimens of CGMs while acquiring x-ray tomographic images at a resolution sufficient to discern individual grains and cement bonds. A toolset is developed to characterise, for the first time, each grain and cement bridge in the specimen, their evolution, and to extract statistically representative measures of the grain-scale processes. Numerically, boundary value problems are solved using the finite element method to bridge experimental observations to analytical predictions, and vice versa, while accounting for the effects of strain localisation. The acknowledgement of grain-scale behaviour within this methodological framework allows for a realistic validation of the constitutive models not only at the scale of the specimen response and its localisation features, but also at the scale of individual grains. This is pivotal in several open engineering problems controlled by the localised evolution of the micro-structure.

Cemented carbides are used in rock tool applications by reason of their beneficial mechanical properties, i.e. a combination of high toughness, wear resistance and hardness. The cemented carbides commonly receive their hardness from tungsten carbides (WC) whereas cobalt (Co) is the dominating binder material. To obtain a beneficial balance of these desired properties, the binder phase can be strengthened by post-sintering treatment to minimize the risk of catastrophic failure. Previous work has shown that the face centered cubic (FCC) cobalt phase is stabilized by a higher degree of dissolved tungsten in the binder. The residual stresses have been related to both further stabilization of the FCC and local transformation to a hexagonal close packed (HCP) phase. By exposing the inserts to mechanical deformation, i.e. inducing stress, the Co-binder material could theoretically transform from FCC to HCP. In this master thesis, five cemented carbides with three different binder phase compositions have been investigated. Additionally, the influence of the carbon content and addition of an alloying element was evaluated. This was done by electron backscatter diffraction (EBSD) analysis of the microstructure of each sample in as-sintered state and after post-treatment to gain better understanding on how the phase stability of the binder is affected by a post-sintering process. In addition, magnetic measurements, hardness-testing and mechanical tests were performed on the materials to evaluate the effect of using different binder compositions. It was found that a low carbon content provides smaller and more rounded WC grains and binder phase dominated by FCC-Co compared to an equivalent material with a high carbon content. A low carbon content furthermore resulted in a more wear resistant material. The addition of alloy MA presented a greater increase in surface hardness after post-treatment and made the materials even more wear resistant compared to the non-alloyed. The non-alloyed material performed better in a test measuring the fracture energy. A material with an Fe-based binder showed the least increase in surface hardness and the highest increase and overall fracture energy. All materials experienced a WC grain size refinement and an increase in their surface hardness after post-treatment. Only one material gave an indication on FCC to HCP phase transformation, no conclusions could be drawn from the other samples.
Hårdmetaller används i bergborrstift på grund av materialets fördelaktiga mekaniska egenskaper vilket innefattar en kombination av hög seghet, hårdhet och bra nötningsmotstånd. Hårdheten uppnås vanligen av volfram karbider (WC) medan segheten ges av en bindefas som oftast är baserad på cobolt (Co). För att få ett material med en bra balans mellan seghet och hårdhet så kan bindefasen stärkas genom en ytbehandling efter sintringen för att minimera risken för att borrstiftet går sönder under användning. I tidigare studier har det framkommit att ytcentrerad kubiskt tätpackad (FCC) cobolt stabiliseras av volfram som lösts i bindefasen. Spänningar som uppkommer på grund av detta har relaterats till vidare stabilisering av FCC-fasen, men även lokal omvandling till hexagonalt tätpackad (HCP) cobolt. Genom att utsätta borrstiften för mekanisk deformation, i.e. inducera spänningar, kan bindematerialet teoretiskt sett omvandlas från FCC till HCP. I detta examensarbete har fem bergborrstift med tre olika bindefassammansättningar undersökts. Därutöver har även inverkan av kolhalten och tillägget av ett legeringsämne utvärderats. Den primära metoden för att genomföra undersöka mikrostrukturen hos de sintrade och efterbehandlade stiften var bakåtspridd elektrondiffraktion (EBSD). Syftet med undersökningen var att öka förståelsen kring bindefasens fasstabilitet då den utsatts för en efterbehandlingsprocess. Även magnetisk mätning, hårdhetstestning och mekanisk prövning utfördes på materialen för att kunna jämföra de olika bindefassammansättningarna mot varandra. Resultaten visade att en låg kolhalt gav ett material med mindre och mer rundade WC korn samt att bindefasen dominerades av FCC-Co jämfört mot ett material med samma bas och hög kolhalt. Därtill uppvisade materialen med låg kolhalt bättre nötningsmotstånd. Legeringen av bindefasmaterialet visade en ökning i ythårdhet efter efterbehandling och gjorde materialen mer nötningsbeständiga än de icke-legerade materialen. De icke-legerade materialen visade däremot på högre krosstyrka. Materialet med en järn-baserad bindefas påvisade minst ökning av ythårdheten och högst ökning samt högsta värde på krosstrykan. Samtliga material visade en förfining av WC kornen och en ökning av ythårdheten efter efterbehandlingen. Endast ett material indikerade omvandling från FCC till HCP, inga slutsatser kunde dras från de övriga proverna.

Hardmetal industry is continuously seeking for high-performance products at reduced costs. In addition, it is strongly struggled by the high and volatile prices of raw materials. At this juncture, producers and end-users are deeply concerned in increasing the performance and enhancing service-life and reliability of engineering products, and replacing current constituents by alternative and less critical materials. Premature and unexpected fracture, together with wear, is the main damage phenomenon limiting the life in most cemented carbide applications. In the vast majority of cases such ruptures stem from the combination of high monotonic and cyclic stresses, together with different damage-related features associated with harsh service conditions, such as corrosion, and thermal shock. Therefore, relevant consideration of fracture toughness and fatigue resistance is required if reliability and lifetime of hardmetals applications is to be increased. Following the above ideas, the purpose of this thesis is to improve the performance and increase the reliability of cemented carbides in rupture-limited applications on the basis of enhanced damage tolerance and reduced fatigue sensitivity through an optimal microstructural design. Within this framework, this investigation is composed of three main subjects covering different aspects related to the performance of hardmetals under service-like conditions. The first two sections are devoted to conduct a comprehensive study on the influence of the microstructure on fracture and fatigue behaviour of hardmetals. The aim of the third section is to evaluate microstructural effects on the tolerance of cemented carbides to service-like damage, induced either by localised corrosion or thermal shock. Main contribution to toughness in cemented carbides derives from plastic stretching of crack-bridging ductile enclaves at the crack wake, referred to as the multiligament zone. Hence, the development of a multiligament zone implies the existence of a rising crack growth resistance (R-curve) behaviour in cemented carbides. This effectiveness of this toughening mechanism is intimately related to the microstructural characteristics. Within this context, the first section of this thesis is dedicated to carry out a detailed investigation of fracture mechanics and mechanisms in cemented carbides, and to propose a relation to capture microstructural effects on the R-curve characteristics of these materials. Strength reduction of hardmetals under the application of cyclic stresses is related to the inhibition of the crack-tip bridging mechanism. For WC¿Co cemented carbides, the degradation of bridging ligaments is mainly associated with an accumulation of the fcc to hcp phase transformation. However, this mechanism does not apply for Ni binders; therefore, it remains unclear if effective fatigue susceptibility of Co-base hardmetals is comparable to that of cemented carbides consisting of alternative binders. Moreover, hardmetals exhibit crack-deflection as an additional toughening mechanism, but contrary to the case of crack-bridging, it is immune to fatigue loads. The effective action of this toughening mechanism is speculated to increase with rising carbide mean grain size. Hence, the second part of this thesis is devoted to study and understand the fatigue sensitivity of cemented carbides consisting of binders with deformation mechanisms beyond phase transformation as well as medium/coarse microstructures. Finally, the third section of this thesis consists of a systematic study on the influence of the microstructure on damage-related features induced by either thermal shock or corrosion, in order to set out guidelines for optimal microstructural design. In doing so, the structural integrity of damaged cemented carbides is assessed on the basis of residual strength, and microstructural effects on damage tolerance are captured by means of considering induced damage level as a critical parameter.
Por un lado, la industria del metal duro está sumergida en una búsqueda constante de materiales de altas prestaciones a un coste reducido. Por el otro lado, las materias primas tienen precios altos y volátiles, que comprometen la estabilidad del mercado. En esta coyuntura, los productores y los usuarios finales están muy interesados, tanto en aumentar el rendimiento, incrementar la vida útil y mejorar la fiabilidad de estos productos, como en su sustitución por materiales alternativos y considerados menos críticos. En este contexto, el desgaste y la ruptura prematura son los dos principales mecanismos que limitan la vida útil de las aplicaciones de metal duro. En la gran mayoría de los casos las rupturas prematuras derivan de la combinación de altas tensiones, tanto monótonas como cíclicas, con el daño inducido durante la vida en servicio, como la corrosión, y el choque térmico. Por lo tanto, con el fin de aumentar fiabilidad en estas aplicaciones, es necesario entender los mecanismos de daño y fallo en estos materiales. Así, el propósito de esta tesis es mejorar el rendimiento y aumentar la fiabilidad de los carburos cementados a partir del desarrollo de materiales con una mayor tolerancia al daño y una menor sensibilidad a fatiga, a través de un óptimo diseño microestructural. La presente investigación se compone de tres partes que abarcan diferentes aspectos relacionados con el desempeño de los metales duros en condiciones de servicio. Las dos primeras secciones están dedicadas a realizar un estudio general sobre la influencia de la microestructura en el comportamiento a fractura y fatiga del metal duro. El objetivo de la tercera sección es evaluar los efectos microestructurales en la tolerancia al daño de los carburos cementados, ya sea inducido por corrosión o por choque térmico. El principal mecanismo de tenacidad en los carburos cementados reside en el estiramiento plástico de ligamentos metálicos de puenteo que se forman detrás de la punta de la grieta, llamada la zona de multiligamentos. El desarrollo del mecanismo de puenteo implica un incremento de la resistencia a fractura a medida que aumenta la longitud de la grieta. Este mecanismo es conocido como curva-R y su eficacia está íntimamente relacionada con las características microestructurales del material. Así, la primera parte de esta tesis doctoral está dedicada a llevar a cabo una investigación detallada de los mecanismos de fractura en los carburos cementados, y a proponer una relación que permita captar los efectos microestructurales en las características de curva-R de estos materiales. Por otro lado, la segunda parte de la tesis está dedicada a estudiar la influencia de la microestructura, incluyendo tanto el tamaño de grano de la fase carburo como el contenido de la fase ligante y su naturaleza química, en la sensibilidad a fatiga de los carburos cementados. Así, se ha prestado una atención particular en estudiar el comportamiento a fatiga de los carburos cementados con base níquel y en su comparación con los de base cobalto. Por otro lado, también se ha estudiado la influencia del tamaño de grano en la deflexión de grieta como un mecanismo adicional de aumento de tenacidad, inmune a las solicitaciones cíclicas. Por último, la tercera sección de esta tesis consiste en un estudio sistemático de la influencia de la microestructura de los carburos cementados en su tolerancia al daño, inducido tanto por corrosión como por choque térmico, con el fin de establecer las directrices para un diseño microestructural óptimo. De este modo, la integridad estructural de carburos cementados se evalúa sobre la base de su resistencia residual a flexión después de la inducción de daño

Cemented carbides are composite materials widely used in different industry fields within applications involving wear, due to their outstanding wear resistance. The most commonly used are WC-Co grades, for Co wettability with the carbide and adhesion characteristics. Emergence of new applications, the existence of advanced characterization techniques, economic and environmental aspects, among others, encourages the development of a new cemented carbides generation containing other binding phases as Ni and Fe or alloys of them. Furthermore, Co powder has been classified as very toxic for the human health and the combination carbide-cobalt hardmetals dust has shown to be even more toxic than both pure cobalt and tungsten. The success of substitution of the main constituents of cemented carbides, have been commonly measured in terms of their final mechanical properties at macroscale such as hardness, toughness and transverse rupture strength; and structural integrity under service-like conditions, such as corrosion resistance, thermal shock and fatigue resistance. In this sense, general framework of microstructural effects – carbide mean grain size, volume fraction and chemical nature of constitutive phases - on the mechanical response of cemented carbides is well established at the macroscale. However, assessment of the individual role of the binder and carbide phases at local scale i.e. microscale, is yet to be studied in depth. Within micromechanical testing, special attention has being paid to the micropillar compression approach because its advantages: the stress-state is nominally uniaxial, allowing a straight conversion of the measured load-displacement data into flow curves; sample preparation by means of Focused Ion Beam (FIB) milling is a relatively easy machining route; it involves the use of a conventional nanoindenter with a flat-end tip; and, it can be performed ex-situ or in-situ by using Scanning Electron Microscopy (SEM) or Transmission Electron Microscopy (TEM) techniques. However, attention have to be paid to sample sizes since it has been well established that intrinsic properties of crystalline materials such as yield stress and strength, can be greatly influenced by extrinsic factors such as volume. For instance, results have evidenced an inverse relation between hardness and the indentation depth at the micro- and nanometric length scales. Regarding cemented carbides, recent studies showed that changes in volume fraction of binder and carbides in samples can lead to wide scatter in results of Young’s modulus measured at the microscale. Following the above ideas, in this PhD thesis uniaxial compression of micropillars and nanoindentation have been selected to evaluate the role of binder and carbides regarding their chemical nature and microstructural dimensions, i.e. carbide mean grain size and binder mean free path, in the mechanical properties and response of cemented carbides at local scales. This thesis is presented by a compendium of scientific publications in which several specific objectives are studied individually. In the first and second publications the sample size and the volume fraction of constitutive phases within the micropillar are studied respectively. Results allowed to overcome the size effect issue – usually found when testing in the micro or nanometer regime – by selecting an appropriate sample size, to accomplish reliability on the mechanical properties evaluated at local length scales. Third and fourth publications are devoted to investigating the mechanical properties of cemented carbides with partial or total substitution of WC or Co as main constitutive phases based on their intrinsic mechanical properties and behavior. Outcomes evidence that small scale testing of complex composite materials such as cemented carbides by means of uniaxial compression of micropillars and nanoindentation, allows to evaluate the role of each constitutive phase on their mechanical behavior.
Los carburos cementados son materiales compuestos ampliamente utilizados en diferentes campos de la industria dentro de aplicaciones que implican desgaste, debido a su excelente resistencia al mismo. Los más utilizados son los grados WC-Co, debido a la buena mojabilidad del Co con el carburo. La aparición de nuevas aplicaciones, la existencia de técnicas avanzadas de caracterización, y aspectos económicos y ambientales, fomenta el desarrollo de una nueva generación de carburos cementados que contiene otras fases ligantes como Ni y Fe o sus aleaciones. Además, el polvo de Co ha sido clasificado como muy tóxico para la salud humana y la combinación de polvo de metal duro de carburo y cobalto ha demostrado ser aún más tóxico que el cobalto y el tungsteno puros. El éxito en la sustitución del Co y WC en carburos cementados es medido comúnmente en términos de sus propiedades mecánicas finales a escala macro, como dureza, tenacidad y resistencia; y de su integridad estructural en condiciones de servicio, como resistencia a la corrosión, choque térmico y resistencia a fatiga. En este sentido, los efectos microestructurales (tamaño medio de WC, fracción de volumen y naturaleza química de las fases constitutivas) sobre la respuesta mecánica de estos materiales están bien establecidos a macroescala. Sin embargo, el papel individual cada fase a escala local, es decir, microescala, aún no se ha estudiado en profundidad. Dentro de los ensayos micromecánicos, se ha prestado especial atención a la compresión de micropilares debido a sus ventajas: estado de tensión nominalmente uniaxial, permitiendo la conversión directa de los datos medidos de desplazamiento y carga en curvas de flujo; la preparación de la muestra mediante fresado con haz de iones focalizados (FIB) es una ruta de mecanizado relativamente fácil; implica el uso de un nanoindentador convencional con punta plana; y, puede realizarse ex situ o in situ utilizando técnicas de microscopía electrónica de barrido (SEM) o microscopía electrónica de transmisión (TEM). Sin embargo, se debe prestar atención a los tamaños de muestra, ya que las propiedades intrínsecas de los materiales cristalinos, como el límite elástico y la resistencia, pueden verse muy influidas por factores extrínsecos como el volumen. Por ejemplo, resultados han evidenciado una relación inversa entre la dureza y la profundidad de indentación en las escalas de longitud micro y nanométrica. Con respecto a los carburos cementados, estudios recientes mostraron que cambios en la fracción de volume de ligante y carburos conducen a una amplia dispersión en los resultados del módulo de Young medido a microescala. Siguiendo las ideas anteriores, en esta tesis doctoral se ha seleccionado la compresión uniaxial de micropilares y nanoindentación para evaluar el papel del ligante y los carburos con respecto a su naturaleza química y dimensiones microestructurales, es decir, el tamaño medio del grano de carburo y el camino libre medio del ligante, en las propiedades y respuesta mecánica de carburos cementados a escalas locales. Esta tesis es presentada por un compendio de publicaciones científicas en los que varios objetivos específicos se estudian individualmente. En la primera y segunda publicación se estudia el efecto del diámetro del micropilar y la fracción volumétrica de las fases constitutivas dentro del mismo para superar el problema del efecto del tamaño de la muestra, seleccionando un tamaño apropiado para lograr confiabilidad en las propiedades mecánicas evaluadas localmente. Las publicaciones tercera y cuarta se dedican a investigar las propiedades mecánicas de los carburos cementados con sustitución parcial o total de WC o Co, en función del comportamiento mecánico intrínseco de las fases constitutivas. Los resultados demuestran que las pruebas a pequeña escala de materiales compuestos complejos – como los carburos cementados – mediante compresión uniaxial de micropilares y nanoindentación, permiten evaluar el papel de cada fase constitutiva en su respuesta y propiedades mecánicas. Al hacerlo, se debe seleccionar un tamaño de muestra apropiado para obtener resultados confiables del comportamiento general del material.
Els carburs cimentats – també coneguts com a metalls durs – són materials compostos àmpliament usats a diversos camps industrials en aplicacions que comporten desgast, com en eines de tall, mecanitzat o trepat, a causa de la seva excepcional resistència al mateix. Els carburs cimentats més comunament usats són graus de WC-Co, per les característiques d’humectabilitat de cobalt (Co) amb el carbur de tungstè (WC) i la seva adhesió. L’aparició de noves aplicacions, l’existència de tècniques de caracterització avançades, aspectes econòmics i ambientals, entre d’altres, fomenta a el desenvolupament d’una nova generació de carburs cimentats que continguin altres fases d’unió com níquel (Ni) i ferro (Fe) o els seus aliatges. A més, la pols de Co ha estat classificada com a molt tòxica per a la salut humana i la combinació de pols de metall dur carbur-cobalt ha demostrat ser encara més tòxica que el Co o el W purs. L’èxit de la substitució dels constituents principals dels carburs cimentats es mesura habitualment en termes de propietats mecàniques finals, com la duresa, la tenacitat de fractura Palmqvist i la resistència a fractura transversal (TRS) a escala macroscòpica; i en termes d’integritat estructural en condicions similars a servei, com ara la resistència a corrosió, resistència a xocs tèrmics i fatiga, etc. En aquest sentit, el marc general dels efectes de les característiques microestructurals – mida mitjana dels carburs i fracció de volum i naturalesa química de les fases constitutives – en la resposta mecànica dels carburs cimentats està ben establerta en l’escala macroscòpica. No obstant això, encara cal estudiar en profunditat el paper individual de la fase lligant i dels carburs en l’escala local, és a dir, a l’escala micromètrica. Pel que fa als assajos micromecànics, s’ha prestat especial atenció a la compressió de micropilars gràcies als seus avantatges: l’estat de tensions és nominalment uniaxial, permetent una conversió directa de les mesures càrrega-desplaçament a corbes de flux; la preparació de mostres mitjançant un microscopi de feix de ions (FIB) és una tècnica de mecanitzat relativament senzilla; implica l’ús d’un nanoindentador convencional amb una punta plana; i es pot realitzar ex-situ o in-situ mitjançant un microscopi electrònic de rastreig (SEM) o de transmissió (TEM). Tot i això, cal parar atenció a les dimensions de les mostres, ja que està ben establert que les propietats intrínseques dels materials cristal·lins, com ara la tensió i la resistència, poden estar molt influïdes per factors extrínsecs com ara el volum. Per exemple, els resultats han evidenciat una relació inversa entre la duresa i la profunditat d’indentació a les escales micro- i nanomètriques. Respecte als carburs cimentats, estudis recents han demostrat que canvis en la fracció volumètrica de lligant i carburs comporta una àmplia dispersió en els resultats de mòdul de Young mesurat a la microescala. Seguint aquestes idees, en aquesta tesi doctoral s’ha seleccionat la compressió uniaxial de micropilars i nanoindentació per avaluar el paper del lligant i els carburs respecte la seva naturalesa química i dimensions microestructurals, és a dir, grandària mitjana del carbur i camí lliure mig del lligant, en les propietats mecàniques dels carburs cimentats i la seva resposta mecànica a escales locals. Aquesta tesi es presenta com a compendi de publicacions científiques en les quals s’estudien objectius específics individualment. La primera publicació té com a objectiu avaluar l’efecte del diàmetre del micropilar en la resposta micromecànica del WC-Co. A la segona publicació, s’investiguen l’efecte de la mitja mitjana del gra de WC i la fracció de volum de les fases de carbur i lligant. Els resultats han permès superar el problema de l’efecte de mida – habitual quan s’assaja a escales micro- i nanomètrica – seleccionant una mida de mostra adequada per tal d’aconseguir propietats mecàniques fiables avaluades a escales locals. La tercera i quarta publicacions estan dedicades a investigar les propietats mecàniques dels carburs cimentats amb substitució parcial o total de WC o Co com a fase constitutiva principal. En aquest sentit, en la tercera publicació s’usa la tècnica de nanoindentació per avaluar la duresa intrínseca de les fases constitutives i la tensió de flux del lligant constret en un carbur cimentat WC-(W,Ti,Ta,Nb)C-Co. Finalment, en el quart treball s’han estudiat tres materials, un amb Co i dos amb substitució parcial o total de Co com a lligant, respectivament, per tal d’investigar la influència de la naturalesa química del lligant en la resposta mecànica global dels carburs cimentats, segons fenòmens de deformació plàstica i mecanismes de fallada induïts per compressió uniaxial de micropilars. Els resultats derivats de la investigació realitzada durant aquesta tesi doctoral demostren que els assajos a escala petita de materials compostos complexos com ara els carburs cementats mitjançant compressió uniaxial de micropilars i tècniques de nanoindentació permeten avaluar el rol de cada fase constitutiva en les propietats i resposta mecàniques. Per fer-ho, cal seleccionar una mida de mostra adequada per tal d’obtenir resultats fiables del comportament global del material.

[Truncated abstract] Characterising the behaviour of calcareous sediments that possess some degree of bonding between their constituents has attracted worldwide research interest in recent years. Although many recent studies have made significant contributions in delineating the behaviour of these sediments, there is still paucity of information particularly on the cyclic behaviour of cemented calcareous soils. This thesis describes in detail the characteristic features of cemented calcareous soils and proposes methods for characterising their cyclic behaviour. Two different calcareous soils Goodwyn (GW) and Ledge Point (LP) soils representing extreme depositional environments were examined in this study. Artificially cemented sample were created using the CIPS (Calcite Insitu Precipitation Systems) technique, considering its superiority over other most commonly available cementation techniques in replicating the natural pattern of cementation, and the behaviour of natural calcarenite under monotonic loading conditions. The experimental program involved triaxial testing of both uncemented and calcite-cemented calcareous soils under different loading conditions, i.e. isotropic compression tests to high-pressure (16 MPa), monotonic shearing tests, undrained cyclic shearing tests and undrained monotonic post-cyclic shearing tests. Significant emphasis has been placed on the cyclic behaviour of these soils. Internal submersible LDVTs were used for the accurate and continuous measurement of strain down to about 10-5

Several well established techniques of soil stabilisation and soil reinforcement are available to improve properties of geotechnical materials. However, the addition of fibre into soils has its unique potential as a reinforcing agent. This is because a friction between fibre and soil particles increases the bonding between the particles of soils and this can improve the plasticity, stress-strain behaviour and failure characteristics of both cemented and uncemented soils. It also reduces the brittleness of the cemented sand. Numerous experiments on fibre-reinforced granular materials have been carried out by several researchers. However, the behaviour of fibre-reinforced cemented granular soils has not been fully understood yet. Furthermore, most experimental studies of fibre reinforced cemented materials have been carried out at relatively low confining pressures. As a result, more experiments are still needed to understand complicated behaviour of soil-cement-fibre composite materials. The main objective of this thesis is to analyse the behaviour of fibre reinforced cemented sand under wide range of confining pressures. For this GDS high pressure triaxial cell apparatus and Bishop and Wesley conventional triaxial cell apparatus have been used to carry out the tests at wide range of confining pressures from 50kPa to 20MPa. Drained and undrained tests have been carried out on polypropylene fibre reinforced sand with and without the addition of cement. Samples with varying fibre and cement content were prepared by the method of undercompaction and were cured for 28 days prior to testing. The experimental results indicate that there is a significant effect from the addition of fibre and/or cement contents and confining pressures on the mechanical behaviour of Portaway sand. Particularly, these effects were noted in drained and undrained triaxial tests, particularly peak strength, strength parameters, shear banding, particle crushing, yielding, and stress-dilatancy relationships. The addition of fibres increases the peak, yield, and ultimate strengths. Increase in confining pressure also increases the strength but the individual effect of the addition of fibres was more pronounced at low confining pressures. Progressive suppression in the dilation by the gradual increase in confining pressures as well as an increase in dilation with the addition of fibres during triaxial compression was also worth noticeable. Although, no noticeable affect was observed in isotropic compression due to the addition of fibre in both cemented and uncemented sand. An extensive series of tests were carried out but due to time constraint only one type and length of fibre was used. Therefore, more research needs to be carried out at different fibre lengths and types in order to see that whether these change the behaviour observed in this research.

In this thesis, a new methodology for the design of CRF under static and dynamic loading conditions is developed. First a comprehensive literature review of the backfill material is accomplished which included a review of CRF operations and laboratory testing programs. This is followed by a review of numerical modelling studies performed on CRF. Based on the findings from literature review, two numerical models for CRF are developed using FLAC3D code. One of the models considers stopes to be inclined at about 67 degrees and the other considers vertical stopes. The numerical models are then used to study different aspects of CRF practice including the loading conditions, blast-induced vibrations from adjacent production stopes, vertical block mining method, CRF properties, CRF placement method and segregation. A case study mine CRF model is then constructed in accordance with site conditions and the geomechanical data provided by the mine. The case study mine numerical model is calibrated with in-situ stress measurements previously conducted at the case study mine. Mining and backfilling sequence is simulated with the calibrated model and the secondary stope is mined out in three lifts. In-situ blast vibration monitoring experiment in CRF is performed at the case study mine. Two geophones are installed: one inside CRF and the other on the surface of the CRF, and all three production blasts of the adjacent secondary stope are recorded. The detailed procedure, installation and results are presented in the thesis. The results are also used for numerical model calibration. To calculate damping coefficient for the model and blast load magnitude an equivalent cavity model is constructed. The equivalent cavity model is applied with reduced borehole pressure and the model is compared with charge-weight scaling law. The blast load and damping coefficients are extracted from equivalent cavity model and applied as input parameters for the CRF model. The numerical model is calibrated using blast load and damping coefficients obtained from the equivalent cavity model by computing the blast vibrations at a location similar to the one on site. The model is calibrated for all three blast lifts and results are presented. Finally, a CRF failure control study is carried out which encompasses the base case scenario of a planned stope at the case study mine, selective mining strategy for mining high grade ore, strategy of leaving an ore skin, tactically varying CRF properties vertically in CRF. In addition a parametric study is conducted to improve CRF stability by varying CRF properties and possible trends are presented. All results compare static loading versus blast loading scenario on CRF. The results include comparison of backfill stresses and profiles of peak particle velocity. Results of all analyses are presented along with the findings, conclusions, suggestions for future work and statement of contribution.
Dans cette thèse, une nouvelle méthodologie pour la conception de CRF sous des contraintes statiques et dynamiques est développée. Premièrement, un examen de la littérature existante à été accompli. Les opérations minières employant le CRF sont examinées ainsi que les programmes d'essai en laboratoire et les études de modélisation numérique effectuées pour le CRF. Basés sur l'examen de la littérature existante, deux modèles numériques pour le CRF on étés développé en utilisant FLAC3D. Le premier modèle considère un pendage de 67 degrés pour les chantiers, lorsque l'autre considère des chantiers verticaux. Ces modèles numériques sont ensuite utilisés pour l'étude de différents aspects de la pratique du CRF tels que les conditions de chargement, les vibrations de tir, les propriétés du CRF, la méthode de placement du CRF, ainsi que la ségrégation du CRF. Un modèle pour la mine de l'étude de cas est ensuite construit en tenant en compte les conditions du site ainsi que les données geo-mecaniques fournies par la mine. Le modèle pour la mine de l'étude de cas est calibré selon les mesures des contraintes in-situ effectués à la mine. La séquence d'abattage et de remblayage est ensuite simulée avec le modèle numérique calibré et les chantiers secondaires sont extraits en trois étapes. Les vibrations de tir in-situ sont mesurées à la mine de l'étude de casé. Deux géophones sont installés : un à l'intérieur du CRF et l'autre à la surface du CRF, et les trois sautages de production du chantier adjacent sont enregistrés. La procédure de l'installation et les résultats obtenus avec le géophone sont présentés dans la thèse. Les résultats sont utilises pour valider le modèle numérique. Le chargement de tir ainsi que les coefficients d'amortissement sont extraits d'un modèle de cavité en calculant les vibrations de tir à la même position que celle du site. Le modèle est validé pour les 3 étapes de l'abattage du chantier et les résultats sont présentés. Finalement, une étude sur le contrôle de stabilité du CRF est effectuée. Cette étude englobe un scenario de base d'un chantier planifié à la mine de l'étude de cas, une stratégie d'abattage sélectif du minerai de haute teneure, une stratégie ou une couche de minerai est laissée dans le chantier, et une variation verticale planifiée des propriétés du CRF. De plus, une étude paramétrique est conduite pour améliorer la stabilité du CRF en variant les propriétés du CRF. Les tendances possibles sont présentées. Tous résultats comparent le chargement statique avec le chargement dynamique sur le CRF. Les résultats incluent une comparaison des contraintes du remblai ainsi que le profile de la vitesse de crête des particules. Les résultats de toutes les analyses sont présentés avec les constatations et conclusions.

Sandvik Coromant is a leading supplier of tools for the metalworking industry. Sandvik Coromant launches every year thousands of new articles. A number of manufacturing techniques are available for single piece production of tungsten carbide inserts. These methods have their advantages and their disadvantages. Some of these disadvantages might be covered by using milling, however, milling tungsten carbide is hard. An interesting aspect of brittle materials that is researched over the last years is that its properties can be changed locally by applying a large hydrostatic pressure. By doing this, brittle materials like silicon, glass and as well tungsten carbide can be successfully cut. However, this research is based on testing the hypothesis of cutting brittle materials, not on applicability in industry. Due to confidentiality reasons, it is not possible to include more information in this abstract.
Sandvik Coromant är en ledande tillverkare från verktyg för metallbearbetningsindustrin. Sandvik Coromant introducerar varje år tusende nya produkter.Det finns några tillverkningsmetoder för enkelstyckstillverkning av hårdmetall vändskär. Dessa metoder har deras fördelar och nackdelar. Några av dessa nackdelar kan tacklas genom att använda fräsning, men hårdmetall är hårt att fräsa. En intressant aspekt av spröda material som har undersökts under de senaste åren är att egenskaper kan ändras lokalt om ett högt hydrostatiskt tryck tillämpas. Genom att göra så, spröda material som silicium, glas och även hårdmetall kan skäras. Dock bygger forskningen på att testa hypotesen att skära spröda material, inte på dess användbarhet inom industrin. Av sekretesskäl, är det inte möjligt att ta med mer information i denna sammanfattning.

Underground mining is a mineral acquisition technique that is critical to global economies, and human technological advancements. As shallow resource reserves are depleted, mine depths are increasing to accommodate global mineral demand. Increases in mine throughputs and excavation depths pose increased environmental concerns. Tailings surface disposal, and underground mine support are two considerable environmental and geotechnical factors of concern in current day mining. Underground waste disposal has been adopted by the mining industry in many forms. Cemented paste backfill (CPB) is a common best management practice developed to tackle these two specific resource industry related issues worldwide. CPB is a cement-stabilized material composed of tailings, water, and hydraulic binder. Tailings disposal areas on the earth’s surface are reduced by disposing of tailings in subsurface stopes that have been previously excavated. This increases underground safety by providing structural support to the mine. There are also economic benefits to this practice, as the additional support allows for adjacent pillars to be excavated. Although CPB greatly reduces tailings exposure to atmospheric elements, there are still underground environmental factors that must be considered with respect to environmental performance. CPBs are porous media, meaning they are susceptible to leaching of naturally occurring metals that are no longer in a stable condition as they were when incorporated in the parent rock. Arsenic and lead are metals of concern due to their association with many ore bodies. Leaching of these unstable metals may be influenced by the backfill curing temperature and the chosen hydraulic binder. Curing temperatures may be influenced by geographic location, local stope geology and depth, hydration and transport, among others. Hydraulic binders are chosen based on availability, cost, and desired mechanical properties of the paste. In this research, the effect of curing temperature and binder composition on the leachability of CPB are studied. ASTM C 1308 leaching protocol is used to determine the leachability of six CPBs. In addition, microstructural techniques (Powder X-Ray Diffraction, Mercury Intrusion Porosimetry, and Scanning Electron Microscopy) are used to relate the microstructural properties of the CPB to the leaching characteristics. Results reveal that CPBs cured with ordinary Portland cement (OPC) leach significantly less than CPBs cured with an OPC/Blast furnace slag (Slag) binder (50% blending ratio) as a result of CH consumption in slag hydration. Both CH and C-S-H are responsible for immobilizing arsenic in cement stabilized materials. OPC-CPBs contain greater relative quantities of CH, which aids in arsenic immobilization. Between the range of 2°C and 35°C OPC-CPB performed better at lower curing temperatures. Lower curing temperatures are favoured in OPC-CPB because the pore surface greater than the threshold pore diameter is reduced. Alternatively, OPC/Slag-CPB exhibited a decrease in cumulative mass leached at higher curing temperatures. The difference in cumulative mass leached by the OPC/Slag-CPBs is also related to the pore surface, and threshold pore diameter.

The magnetic properties, coercivity, Hc, and weight-specific magnetic saturation, CoM, are two important quality characteristics in cemented carbides and ceramic metals, cermets. These properties give information about grain size and binder phase content, and are influenced by the different stages in the sintering process. This master thesis aim to investigate how the magnetic properties in cemented carbides are influenced by the top temperature during sintering and how the sintering processes used for cermets can be optimized in order to gain better magnetic properties in the final products. During the first part of the project, the temperature range investigated was 1380°C–1520°C. The results indicate that Hc in cemented carbides has a strong temperature dependence, where increasing top temperature results in lower Hc. In order to have approval limits for the furnace control pieces that follow the process directives, the limits used today need to become narrower. Furthermore, the results show that CoM also has a temperature dependence, although not as strongly as Hc. During the second part of the project, already existing data of the magnetic properties in four different cermet grades were evaluated. The results indicate that the two sintering processes used in the DDK furnace are generating too high results in Hc and CoM. Optimization tests were conducted and changes implemented in order to gain better results, where the DJ1430 process now has an increased time during the solid state sintering and the DF1480 process now has an increased time during the liquid phase sintering.

Considering the similarity between the mechanical behavior of artificially cemented soils and rock masses, this study proposes a methodology to obtain the envelopes resistance of artificially cemented soils, using the Hoek-Brown failure criterion. The proposed methodology consists basically in performing two triaxial tests, with the soil non-cemented and cemented with a high cement content, and estimate the strength envelopes for intermediate cement contents, using the equations presented in this research. To develop the methodology, initially, a number of unconfined compression tests and triaxial tests were carried out in order to quantify the influence of the porosity/cement ratio (n/Civ) on the strength parameters of the cement mixtures used. From the tests results and the Hoek-Brown failure criterion, new equations were developed to calculate the envelope parameters (a, m, s), as functions of porosity/cement ratio. The proposed method was applied to triaxial tests data presented in four different studies and the results showed that the Hoek-Brown envelope is suitable to represent the resistance of artificial cemented soils, being able to incorporate the effects caused by the confining pressure and by the cement content. The envelopes estimated and those obtained from the triaxial tests were very close, indicating that the proposed methodology can be used with a reasonable degree of reliability. The results obtained with the proposed methodology were used to simulate, by the Finite Element Method, the pressuresettlement behavior and the variation of the safety factor of a shallow foundation bearing on a double-layered system formed by an artificially cemented soil layer overlaying a soil stratum. The simulations were performed using as variables the cement content of the enhanced layer and the relationship between the thickness of the treated layer (H) and the diameter of the foundation (D). The results show that the use of artificially cemented layers considerably increases the vertical pressure required for an specific settlement and also the foundation safety factor. Thus, the execution of shallow foundations, replacing deep foundations, becomes feasible
Considerando a semelhanÃa existente entre o comportamento mecÃnico dos solos artificialmente cimentados e dos maciÃos rochosos, o presente trabalho propÃe uma metodologia para a obtenÃÃo das envoltÃrias de resistÃncia dos solos artificialmente cimentados, utilizando o critÃrio de ruptura geral de Hoek-Brown. A metodologia proposta consiste, basicamente, em realizar dois ensaios triaxiais, um com o solo nÃo cimentado e outro com o solo cimentado com um teor de cimento elevado, e estimar as envoltÃrias de resistÃncia para os teores de cimento intermediÃrios, atravÃs das equaÃÃes desenvolvidas. Para o desenvolvimento da metodologia, inicialmente, foram realizados ensaios de compressÃo simples e triaxiais nÃo drenados, com o objetivo quantificar a influÃncia do fator vazio/cimento (n/Civ) sobre os parÃmetros de resistÃncia das misturas cimentadas utilizadas. A partir dos resultados dos ensaios de resistÃncia e da equaÃÃo geral do critÃrio de Hoek-Brown, foram desenvolvidas equaÃÃes para calcular os parÃmetros da envoltÃria (a, m, s), em funÃÃo do fator vazio/cimento. A metodologia proposta foi aplicada aos resultados dos ensaios triaxiais apresentados em outros quatro trabalhos e os resultados mostraram que a envoltÃria de Hoek-Brown à adequada para representar a resistÃncia dos solos artificialmente cimentados, sendo capaz de incorporar os efeitos causados pela tensÃo confinante e pelo nÃvel de cimentaÃÃo. As envoltÃrias estimadas e as obtidas com os ensaios triaxiais ficaram bem prÃximas, indicando que a metodologia proposta pode ser empregada com um razoÃvel grau de confiabilidade. Os resultados obtidos com a metodologia proposta foram utilizados para simular, atravÃs do MÃtodo dos Elementos Finitos, o comportamento carga-recalque e a variaÃÃo do fator de seguranÃa de uma fundaÃÃo superficial assente sobre um sistema de dupla camada, sendo a superior cimentada. As simulaÃÃes foram realizadas utilizando como variÃveis o teor de cimento da camada reforÃada e a relaÃÃo entre a altura da camada cimentada (H) e o diÃmetro da fundaÃÃo (D). Os resultados obtidos mostram que a utilizaÃÃo de camadas artificialmente cimentadas eleva consideravelmente as tensÃes verticais necessÃrias para um recalque relativo especÃfico e, tambÃm, o fator de seguranÃa da fundaÃÃo. Com isso, a execuÃÃo de fundaÃÃes superficiais, em substituiÃÃo a fundaÃÃes profundas, torna-se viÃvel.

Cemented carbide powder production is the first step in the manufacturing of cemented carbide inserts.The quality of the powder affects the successive process steps in the production of the cemented carbide inserts. The powder is produced by spray drying of a slurry. The slurry consists of polymer, water, ethanol, and dry components. The operating conditions of the spray dryer have been studied greatly to optimize the powder properties but less is known about the influence of the slurry on the powder. This work examines the effect of slurry composition on the cemented carbide powder properties. The work is necessary to predict optimum slurry composition to produce good quality cemented carbide powders. To characterise the powders, flowability, density, particle morphology and hollowness of the powder granules were measured for different slurry compositions. No direct correlation was observed between slurry viscosity and the powder properties but a change in the amount of raw material and organic additives in the slurry affected various powder properties. An optimum slurry composition was obtained which can produce better quality of cemented carbide powder. Additionally, it was found that an increase in slurry viscosity can hinder the spray drying process.
Tillverkning av hårdmetallpulver är det första steget i tillverkningen av hårdmetallinsatser. Pulverkvaliteten påverkar de successiva processstegen vid tillverkningen av hårdmetallinsatserna. Pulvret framställs genom spraytorkning av en uppslamning. Uppslamning består av polymer, vatten, etanol och torra komponenter. Driftförhållandena för spraytork har studerats mycket för att optimera pulveregenskaperna, men mindre är känt om påverkan av uppslamningen på pulvret. Detta arbete undersöker effekten av uppslamningskomposition på egenskaperna för hårdmetallpulver. Arbetet är nödvändigt för att förutsäga optimal uppslamningskomposition för att producera hårdmetallpulver av god kvalitet. För att karakterisera pulvren mättes flytbarhet, densitet, partikelmorfologi och hålighet hos pulvergranulerna för olika uppslamningskompositioner. Ingen direkt korrelation observerades mellan uppslamningsviskositet och pulveregenskaperna men en förändring i mängden råmaterial och organiska tillsatser i uppslamningen påverkade olika pulveregenskaper. En optimal uppslamningskomposition erhölls som kan ge bättre kvalitet på hårdmetallpulver. Dessutom fann man att en ökning av uppslamningsviskositeten kan hindra spraytorkningsprocessen.

Magnetic measurements are useful tools for quality control of cemented carbides. Previous work at Sandvik Mining and Rock Technology has shown that the coercivity increases with increased cooling rate during sintering for a specific grade.  This study aims to investigate why the coercivity changes with the cooling rate and if this is true for other cemented carbide grades as well. Three different cemented carbide grades were sintered with different cooling rates and evaluated with coercivity, Cobalt-magnetic saturation and hardness measurements, and with microscopy and Electron Backscatter Diffraction analysis. It was found that the coercivity increased with increasing cooling rates for the previously studied grade, but not for the two other grades. It was expected that the increased coercivity would indicate a decrease in WC grain size, but the results showed that the WC grain size of the fastest and slowest cooling rate were the same. However, a change in size of the Co areas between the WC grains was found. The fast cooled sample showed smaller Co areas than the slow cooled sample. These Co/WC grain boundaries increase the coercivity. An increased fraction of hcp-Co/fcc-Co was also found for the fast cooled material which also increases the coercivity. No relationship between the hardness and the coercivity or the cooling rate was found.   The contiguity for the different grades was also calculated.  No significant difference in contiguity between the different cooling rates of each material was found but the contiguity values between the different materials differed.  This is probably mainly dependent on the different binder contents of the materials.
Magnetiska egenskaper är en viktig del av kvalitetskontrollen av hårdmetaller.  Tidigare forskning hos Sandvik Mining and Rock Technology har visat att koerciviteten hos en hårdmetallsort ökar med ökad kylhastighet vid sintring.  Målet med den här studien är att undersöka varför koerciviteten ökar med kylhastigheten och om detta även gäller andra hårdmetallsorter.  Tre olika hårdmetallsorter sintrades med olika kylhastigheter undersöktes med mätningar av koercivitet, magnetisk mättnat i koboltfasen och hårdhet,  samt med mikroskopi och Electron Backscatter Diffraction analys. Det  visade  sig  att  koerciviteten  ökade  med  ökad  kylhastighet  för  hårdmetallsorten  som  studerats tidigare, men inte för de andra två sorterna.  En ökad koercivitet förväntas visa på en minskad WC-kornstorlek, men resultaten visar att det långsamt kylda och snabbkylda provet hade samma WC-kornstorlek.  Däremot upptäcktes en ändring av storleken på Co-områdena mellan WC-kornen.  Det snabbkylda provet visade en mindre storlek av Co-områdena jämfört med det långsamt kylda provet. Fler Co/WC-korngränser i det snabbkylda provet leder till en ökad koercivitet.  Fraktionen av hcp-Co/fcc-Co-korngränser ökade också för det snabbkylda provet vilket också ökar koerciviteten. Inget samband mellan hårdheten och koerciviteten eller kylhastigheten upptäcktes.  Beräkning av kontiguiteten för de olika sorterna genomfördes också. Ingen signifikant skillnad i koercivitet mellan de olika kylhastigheterna för the olika sorterna hittades,  men kontiguiteten mellan de olika sorterna varierade. Det beror mest troligt på att dom olika sorterna har olika mängd matrismaterial.

Nature aggregates granular materials such as sand, silt and clay into form beach rocks, and other forms of microbialites. A common bio-geo-chemical cementation occurs due to the mineralization of calcium through bacterial enzymatic action, often called Microbial Induced Calcium Carbonate Precipitation (MICP). It is a sustainable construction method. Experimental and Numerical models are presented to study the aggregated granular materials formed due to MICP. The models are applied to investigate different levels of aggregation of sand. The numerical results are compared against experiments and the most important parameters are discussed.

This thesis explores the performance of small scale cemented soil columns produced using soil mixing with cement resulting from bacterially mediated reactions that precipitate calcium carbonate, a process often referred to as bio-cementation. Bio-cementation has received considerable research attention over the last decade as it has the potential to complement existing ground improvement techniques and mitigate environmental concerns with currently used materials. Previous research has concentrated on pumping and injection techniques because of concerns that bacteria will be unable to survive the stresses associated with industrial mixing processes, however it has been difficult to create uniform bio-cemented soil masses. In this thesis the ureolytic bacterium, Bacillus Megaterium, not previously reported in bio-cementation studies, has been investigated to determine its viability and efficiency as a microbe for mediating the calcite precipitation. It has been found that the highest hydrolysis rate is recorded when calcium concentrations are double the urea concentrations, and that significant amounts of calcite can be precipitated in a single mixing process. Unconfined compressive strength (UCS) tests and a series of triaxial tests have been conducted to quantify the effects of the bio-cementation on the mechanical response. Bender elements mounted in the triaxial cell have also been used to monitor the shear wave velocity during curing and shearing. The results of mechanical tests on the bio-cemented sand have been compared with tests on gypsum cemented and uncemented specimens. It has been found that bio-cementation by mixing produces homogeneous specimens with similar strengths and stiffnesses to the commonly used flushing or injection technique. To assess the performance of in-situ mixed, 38 mm diameter, bio-cemented sand columns a small scale in-situ mixing technique was used to create the model columns. Foundation tests have been performed at 1-g in a cylindrical tank with diameter of 600 mm. A significant improvement was observed in the response of foundations when placed on bio-cemented columns, and this was similar to the improvement from more conventional gypsum cements. These tests confirmed the feasibility of using an in-situ mixing technique with bio-cementation and provided valuable insight into the factors that must be considered in developing field applications. This thesis also has demonstrated repair strategies and techniques to encourage healing and self-healing should damage occur in foundations. Results from tests performed to investigate the ability of biocement to repair cemented soil columns are reported.

The mechanical behaviour of cemented granular materials has been an important topic in geotechnical engineering since decades. Historically, most research on ce-mented granular materials has been performed at relatively low confining pressures. Problems relating to cemented granular materials at high-pressure are still not fully understood. However, understanding of the behaviour of cemented granular materials at high-pressure is highly important in deep foundations, particularly for offshore piling, deep mine shafts, high earth dams, and oil-bearing strata. To address the problem, artificially cemented sand specimens with varying degrees of cement contents and initial relative densities were prepared in the laboratory to simulate the natural cementation characteristics. A high-pressure triaxial compression apparatus was utilized to investigate the effect of initial relative density, cement content, and confining pressure on the mechanical behaviour of artificially cemented sand. High-pressure tests including isotropic compression, drained and undrained triaxial shearing and microscopic studies of the materials were carried out on the artificially cemented sand specimens in the Nottingham Centre for Geomechanics laboratory at the University of Nottingham. Complexities with artificial specimen preparation and with high-pressure testing were identified and tackled. The experimental results indicate that there is significant effect of cement contents and confining pressures on the mechanical behaviour of cemented materials. Particularly, these effects were notified on isotropic compression, peaks strength, strength parameters, shear banding, particle crushing, yielding, and stress-dilatancy relationships. For example, reduction in compressibility, reduction in particle crushing and shift in normal compression line by the increase in cement content of the material during isotropic compression were significant. Progressive suppression in the dilation of cemented sand by the gradual increase in confining pressure, increase in the peak strength, developing of curved failure envelope, increase in the yield strength and formation of conjugate shear banding during progressive failure during triaxial compression were worth noticeable. This concludes that the significance of high-pressure and cement content cannot be ignored in the design considerations. However, more research needs to be carried out at further high pressures in order to see the convergence of failure envelopes and the initiation of bond breakage and particle crushing to give a reasonable design framework for foundations.

In today’s inserts used for metal cutting the binder phase consists of cobalt (Co).However, EU’s REACH programme and the U.S’s National Toxicity Programme(NTP) classified Co as toxic/carcinogenic. Therefore, there is a strong need toinvestigate alternative binder phases. This thesis covers sintering and characterisationof cemented carbide with a binder phase consisting of nickel (Ni) and iron (Fe) withthe composition of 85Ni:15Fe. The aim was to study the gradient formation of turninginsert and find sintering processes to achieve a gradient structure with the targetedthickness of 26 microns. Simulations in ThermoCalc provided a suitable composition and a starting point forsintering parameters. The influences of sintering process parameters, such as holdingtime, temperature and counter pressure on the formation of the gradient zone wereinvestigated. Hot isostatic pressing (HIP) sintering was done in order to study thegradient formation as well as to reduce the porosity when needed. Sintered insertswere analysed by light optical microscopy. It was found that there are at least three possible ways to control the formation ofthe gradient: sintering in vacuum with a holding time of 20 min at 1450°C, sintering at1450°C with a counter pressure of 5 mbar nitrogen, and sintering with a counterpressure of 11.5 mbar followed by a double sinter-hip with 55 bar argon atmosphere.However, only the last process fulfilled the microstructure criteria in terms ofporosity and binder phase distribution. It is clear that the formation of gradient zonesin 85Ni:15Fe can be predicted, however calculations and simulations need to beoptimized in order to get more accurate results.

The factors which affect the engineering properties of calcium carbonate cemented soil are examined. The influence of calcium carbonate content, molding moisture content, and confining pressure on the strength characteristics of two types of soil is investigated in two distinct phases of the research. Type A soil, obtained from the University of Arizona Campbell Avenue Farm in Tucson, was used for the artificially cemented specimen stage. It is composed of sand and silt-size particles with some clay and is virtually free of calcium carbonate in its natural state. Sierrita soil, obtained from the Twin Buttes Open Pit Mine south of Tucson, was used for the reconstituted sample stage. It is naturally cemented with calcium carbonate and is composed mainly of sand, gravel, a small amount of silt, and occasional large-sized (boulder and cobble) particles. Specimens for triaxial compression testing were compacted for each phase of the study under carefully controlled conditions. Three test series were carried out on Type A soil artificially cemented with calcium carbonate. Three percentages (0%, 15%, and 30%) on a dry weight basis of the soil were used. Two molding water contents, one dry and one wet of optimum moisture content, were established for each test series. Unconsolidated undrained triaxial compression tests were carried out on oven-dried specimens at three different confining pressures to obtain shear strength parameters. The fabric characteristics of selected specimens were then defined by viewing them under a scanning electron microscope. The results indicate that the strength of the calcium carbonate cemented soil depends on the distribution and not necessarily the content of the cementing agent within the soil mass. Visual examination of the various microstructures of the artificially cemented soil confirmed the hypothesis that strength gain occurs when the calcium carbonate particles are concentrated at the points of contact between soil grains. Visual examination of the fabric of the naturally cemented Sierrita soil showed the microstructure to be highly compressed with weathered calcium carbonate particles dominating the soil structure. The calcium carbonate content was found to range from 14 to 23%. Because of sampling difficulties, an in situ cohesion value for the Sierrita soil could not be obtained from conventional laboratory tests. Therefore, the value was obtained by back analysis of the stability of actual slopes existing at Twin Buttes Mine. Slope stability analyses using Bishop's Modified Method with a search routine based on the Simplex Method of Nelder and Mead were performed. Stability analyses were also performed using strength properties of artificially cemented Type A soil. These analyses showed the relationships among cohesion, friction angle, safety factor, and calcium carbonate content for a specified slope geometry.

The development of alternative binder systems for tungsten carbide (WC) based cemented carbides has again become of relevance due to possible changes in EU regulations regarding the use of Cobalt (Co). A framework for the ICME (Integrated Computational Materials Engineering) based Materials Design is presented to accelerate the development of alternative binder systems. Part one of this work deals with the design of the cemented carbide composite hardness. It has been shown that the intrinsic binder hardness is comparable to a bulk metal alloy and that based on the binder solubilities a solid solution strengthening model developed in this work can be employed. Using a method presented in this work the non-equilibrium, frozen-in binder solubilities can be obtained. Both the design of the binder phase and composite hardness is presented based on a general Materials Design approach. Part two deals with a multiscale approach to model the surface gradient formation. The experimentally missing data on liquid binder diffusion has been calculated using AIMD (Ab initio Molecular Dynamics). The diffusion through the liquid cemented carbide binder has to be reduced to an effective diffusion value due to the solid carbides acting as obstacles that increase the diffusion path. The geometrical reduction of the diffusion has been investigated experimentally using the SIMS (secondary ion mass spectroscopy) technique in WC-Nickel-58Nickel diffusion couples. The geometrical contribution of the so-called labyrinth factor has been proven by the combination of the experiments and in conjunction with DICTRA simulations using the precise liquid AIMD diffusivities. Unfortunately, despite the improved kinetic database and the geometrical diffusion reduction, the surface gradient formation cannot be explained satisfactory in complex cemented carbide grades. Additional, but so far unidentified, contributions have to be considered to predict the surface gradient thickness.

QC 20170919

Soil Stiffness is an important parameter for any geotechnical engineering design. In laboratory tests it can be derived from stress-strain curves or from dynamic measurement based on wave propagation theory. The second method is a more accurate and direct method for measuring stiffness at very small strains. Until now dynamic measurements have usually been obtained manually from the triaxial test. Attempts have been made to automate the procedure but have apparently failed due to the high level of variability in dynamic measurements. Moreover, triaxial tests of soil can be very lengthy and manual dynamic measurements can be very tedious and impractical for long stress-path tests. In this research a computer program has been developed to automate the stiffness measurement (using bender elements) based on the cross- correlation technique. In this method the program records all the peaks and corresponding arrival times in the cross-correlation signal during the test. The stiffness is calculated and displayed on the screen continuously. The Bender Element enabled to get the small strain shear modulus. An arbitrary “Chirp” waveform of 4 kHz frequency was used for this purpose. Subsequently Bender Element test results were checked by ‘Sine’ waveforms of frequencies 5kHz to 20kHz, as well as by manual inspection of the arrival time. This thesis discusses the method and some of the difficulties in truly automating the process. Finally some results from a number of stress path tests on uncemented and cemented calcareous sediments are presented. Bender elements have been used by many researchers to determine the shear modulus at small strain. Most previous studies have used visual observation of arrival time, which is time consuming and often requires some judgement from the operator. This thesis will describe the use of cross-correlation as a method for automation of Gmax measurement. Cross-correlation has been claimed to be unreliable in the past. However, it will be shown that provided several peaks in the cross-correlation signal are monitored it is possible to follow the variation of Gmax throughout consolidation and shearing. The measurement can be made at regular intervals within the software controlling a stress-path apparatus. Details of the apparatus used and practical considerations including selection of waveform and frequency are discussed. A series of drained cyclic triaxial tests was carried out on artificially cemented and uncemented calcareous soil of dry unit weights 13, 15, and 17 kN/m3 and sheared with constant effective confining stress 300 kPa. Gypsum cement contents of 10%, 20% and 30% of the dry soil weight were used. In addition a series of stress path tests were performed on Toyuora sand samples. Results will be presented for two uncemented and one cemented sand. In addition to the bender elements, all tests had internal instrumentation to monitor axial and lateral strains. Results will be presented for Toyura sand to show that the measurements are consistent with those obtained by other methods. Results will also be presented for carbonate sand subjected to a wide range of stress paths. Finally, results will be presented for the carbonate sand cemented with gypsum. The degradation of Gmax of the cemented soil subjected to variety of monotonic and cyclic stress-paths is presented. Analysis of the results includes assessment of the factors influencing Gmax for uncemented sand. Preliminary analysis indicates that in order of importance these are the mean effective stress, the stress history, void ratio and stress ratio. For cemented sand, Gmax is initially constant and independent of stress path. After yielding the modulus degrades, becoming increasingly stress level dependent and eventually approaches the value for uncemented sand. Factors influencing the rate of degradation are discussed. For the Toyuora sand samples the effects of end restraint on the stress-strain response at small strains were investigated. The conventional method of mounting triaxial specimen has the effect of introducing friction between sample and end platen during a compression test. This inevitably restricts free lateral movement of the specimen ends. Frictional restraint at the sample ends causes the formation of 'dead zones' adjacent to the platens, resulting in non-uniform distribution of stress and strain (and of pore pressure if undrained). On the other hand the specimen with 'free' ends maintain an approximate cylindrical shape instead of barrelling when subjected to compression, resulting in a more uniform stress distribution.