Dissertations / Theses on the topic 'Strength of materials'
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1
Soutsos, Marios Nicou. "Mix design, workability heat evolution and strength development of high strength concrete." Thesis, University College London (University of London), 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.308062.
Abstract:
A literature survey of the properties and uses of high strength concrete, defined for this study as having a strength in excess of 60 N/tnm2, has shown that of prime need is a systematic, reproducible procedure for attaining high strength concrete. The "Maximum Density Theory", i.e. the requirement that the aggregate occupies as large a relative volume as possible, has been adopted as an approach to optimisation of the mix proportions. However, this does not consider the effect that the aggregate suIface area has on the requirement of excess paste for lubrication. To investigate the combined effect of void content and surface area, mixes with lower sand proportions than that required for minimum void content were tested for slump. The optimum sand proportion is the one that produces the highest slump, for a particular cement content. This procedure has been called: "The Modified Maximum Density Theory". Having thus optimised the cement and aggregate contents, partial cement replacement by mineral admixtures, at low water-cement ratios, has been investigated in order to assess: a) their contribution to long term strengths, b) their contribution to reducing the heat evolution of concrete mixes, and c) their effect on the workability of concrete. Condensed silica fume (at replacement levels of up to 15%) produced higher compressive strengths than ordinary Portland cement. Ground granulated blast furnace slag (at replacement levels of up to 30%) can be used without decreasing the 28-day strength. Replacement by 20% pulverised fuel ash resulted in a 15% decrease in the 28-day strength and equal strength to ordinary Portland cement concrete at ages beyond 56-days. Temperature measurements during hydration, under adiabatic conditions, have however shown that these replacement levels do not lower the temperature rise at a water-binder ratio of 0.26. The higher levels required for significant temperature reduction will also cause a significant reduction in the strength. To offset this ground granulated blast furnace slag (58%) and pulverised fuel ash (36%) in combination with 10% condensed silica fume 4 were used. These combinations reduced the temperature rise by more than 10°C while the reduction in the 28-day compressive strength was less than 15%. Partial cement replacement by pulverised fuel ash and ground granulated blast furnace slag improved the workability and therefore allowed a reduction in the superplasticiser dosage required for a given slump. The use of condensed silica fume reduces the workability at low superplasticiser dosages, but it has a water-reducing effect above a certain superplasticiser dosage. Results from these studies have been used to formulate guidelines for the proportioning of materials for producing high strength concrete.
2
Wang, Congwei. "On the strength of defective graphene materials." Thesis, Queen Mary, University of London, 2014. http://qmro.qmul.ac.uk/xmlui/handle/123456789/9065.
Abstract:
Graphene is the first 2D material consisting of carbon atoms densely packed into planar structures. Graphene oxide (GO) is the intermediate derivative of chemically-produced graphene, which retains 2D basal plane structures but is also decorated with functional groups along the basal plane and edges. This functionality allows self-assembly of planar sheets into a paper-like material. However, formations of both intrinsic defects within the sheet structures as well as larger scale extrinsic defects in the paper are expected to significantly degrade mechanical performance. Strength provides the most direct evidence of defect related mechanical behaviour and is therefore targeted for understanding defect effects in GO paper. Such evaluations are crucial both from a technological perspective of realizing designed functions and from a fundamental interest in understanding structure-mechanics in 2D nanomaterials. A complete strategy of performing mechanical testing at different length scales is thus reported to provide a comprehensive description of GO strength. Both conventional larger scale mechanical testing as well as novel smaller length scale evaluations, using in situ atomic force microscopy (AFM) combined with scanning electron microscopy (SEM) and optical microscopy as well as structural probing using synchrotron FT-IR microspectroscopy, were applied to GO materials. Results showed that large structural defects determined mechanical properties of GO papers due to stress concentration effects whereas smaller scale intrinsic effects were defined by interfacial defects and stress concentrations within sheets. Synchrotron FT-IR microspectroscopy provided molecular deformation mechanisms in GO paper, which highlighted the interaction between in-plane C=C and cross-linking C=O bonds. A comprehensive description of macroscopic GO paper using evaluations of strength at the range of length scales studied was attempted, with a good correlation between predictions and experimental observations. This thesis therefore provides a hierarchical understanding of the defects impact on the strength of graphene-based materials from the macroscale to the nanoscale.
3
Bi, Wu. "Racking Strength of Paperboard Based Sheathing Materials." Miami University / OhioLINK, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=miami1091059928.
4
Stone, Robert Michael 1957. "Strength and stiffness of cellular foamed materials." Diss., The University of Arizona, 1997. http://hdl.handle.net/10150/289577.
Abstract:
The use of cellular foams as a core material in light-weight optical and structural systems is of considerable interest. Research and development of these systems, however, have been hampered by the lack of material property data and uncertainty in the use of various suggested material characterizations and the associated constants of proportionality. ASTM standards were researched and, for the most part, found inadequate for testing cellular foam materials. The compression, tension and shear test methods developed are presented, as well as the results from physical tests on closed-cell SXATM foam specimens. Based on the test results, material characterizations are presented. Additionally, a parametric study was performed to investigate the behavior of open and closed-cell foams. Twenty-one (21) finite element models were built and seventy (70) analyses were performed to study the effects of cell geometry. Based on the FEA results, material characterizations are presented for the cubic array and the tetrakaidecahedron geometry. The FEA results are compared with the characterizations proposed by Gibson and Ashby and the test results. The validity of the scaling laws are confirmed; however, the proposed constants of proportionality overestimate the modulii a minimum of 50%. New constants are presented for both open-cell and closed-cell foams, as well as additional insights into the effects of cell shape on Poisson's ratio.
5
Violette, Melanie Glenn. "Time-dependent compressive strength of unidirectional viscoelastic composite materials /." Digital version accessible at:, 2000. http://wwwlib.umi.com/cr/utexas/main.
6
Wen, Edward A. "Compressive strength prediction for composite unmanned aerial vehicles." Morgantown, W. Va. : [West Virginia University Libraries], 1999. http://etd.wvu.edu/templates/showETD.cfm?recnum=959.
Abstract:
Thesis (M.S.)--West Virginia University, 1999.Title from document title page. Document formatted into pages; contains ix, 117 p. : ill. (some col.) Includes abstract. Includes bibliographical references (p. 83-84).
7
Yeung, Conson. "Fracture statistics of brittle materials /." View the Table of Contents & Abstract, 2005. http://sunzi.lib.hku.hk/hkuto/record/B31490323.
8
楊光俊 and Conson Yeung. "Fracture statistics of brittle materials." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2005. http://hub.hku.hk/bib/B45015211.
9
Altzar, Oskar. "Surface Characteristics and Their Impact on Press Joint Strength." Thesis, KTH, Mekanisk metallografi, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-205919.
Abstract:
Press fitting is a commonly used method in the assembly of shafts and gearwheels in gearboxes andare using the friction created between them to hold them together. To increase productivity Scania CVAB in Södertälje, Sweden, are going to replace the current hard machining method for layshafts. Whiletesting the new methods in rig it occurred that the gearwheel slipped in tangential direction towardsthe layshaft at a lower torque then with the current method even through all requirements on thelayshafts surface was meet. The purpose and aim with this study is to investigate differences betweenthe methods and to find new requirements for the layshaft. The torque of slip, (Ms) established in atorque test rig and analysis of surface roughness, hardness and microstructure conducted of both thelayshafts and gearwheels. The characteristics of the layshaft surface was also analysed and comparedbetween the different hard machining methods. The study concludes that no correlation between thesurface parameters and the Ms occurred and no major differences in the material between themethods. The study also concluded that the Ms between the layshaft and gearwheel is lower if thelayshaft surface is harder and smoother than the gearwheel surface.
10
Case, Scott Wayne. "Micromechanics of strength-related phenomena in composite materials." Thesis, This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-09122009-040447/.
11
Young, Tyler Blaine. "Early-age strength assessment of cement-treated materials /." Diss., CLICK HERE for online access, 2007. http://contentdm.lib.byu.edu/ETD/image/etd1779.pdf.
12
Branch, James. "Plastic properties of fresh high strength concrete." Thesis, University of Surrey, 2001. http://epubs.surrey.ac.uk/842953/.
Abstract:
This thesis describes the novel test techniques that were developed to measure the parameters associated with the plastic shrinkage, and subsequent possible plastic shrinkage cracking, of high strength concrete. The parameters measured during the first 24 hours after placing were the stress- strain relationship, negative pore pressure and free shrinkage strain development. The plastic behaviour of eight high strength concrete mixes was quantified and these mixes were then tested to assess their propensity towards plastic shrinkage cracking, using restrained ring tests. A review of the parameters associated with plastic shrinkage cracking was carried out. The general view was that as the particle size in a cement matrix gets smaller, then the negative pore pressures developed are greater and hence shrinkage increases. This meant that the presence of secondary cementing materials, of very small diameter, such as microsilica, in high strength concretes would explain their apparent susceptibility to plastic shrinkage cracking. Eight high strength concrete mixes were tested in exposed and sealed conditions. It was found that when tested in sealed conditions none of the parameters measured presented itself as the sole driving force behind plastic shrinkage or plastic shrinkage cracking. Also, when cured in sealed conditions, none of the mixes tested in the restrained ring test apparatus cracked. When tested in exposed conditions, the presence of wind had little effect on the stress-strain relationship of the mixes tested. However the presence of wind seemed to cause negative pore pressures to develop earlier than in the sealed samples and increased free shrinkage by 3 to 40 times depending on the mix. The samples that exhibited the highest free shrinkage strains, in exposed conditions, were the mixes that cracked when tested in the restrained shrinkage rings. The mixes that cracked all contained microsilica and these mixes did not crack when the same mixes were tested without microsilica. Polypropylene fibres were found to reduce the cracked area of the samples that cracked. The supplementary cementing materials used in this study were ground granulated blast furnace slag, metakaolin, microsilica and pulverised fuel ash.
13
Ganneau, Francois P. 1979. "From nanohardness to strength properties of cohesive-frictional materials : application to shale materials." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/28626.
Abstract:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2004.Includes bibliographical references (p. 213-221).
Advanced experimental and theoretical micromechanics such as nanoindentation makes it possible today to break down highly heterogeneous materials to the scale where physical chemistry meets (continuum) mechanics, to extract intrinsic material properties that do not change from one material to another, and to upscale the intrinsic material behavior from the sub-microscale to the macroscale. While well established for elastic properties, the extraction of strength properties of cohesive-frictional materials from nanoindentation tests has not been investigated in the same depth. The focus of this thesis is to investigate in depth the link between nanohardness of cohesive-frictional materials and strength properties. To address our objectives, we develop a rational methodology based on limit analysis theorems and implement this methodology in a finite element, based computational environment. By applying this technique to indentation analysis, we show that it is possible to extract the cohesion and the friction angle from two conical indentation tests having different apex angles. The methodology is validated on a model cohesive-frictional material, bulk metallic glass, and a first application to a highly heterogeneous natural composite material, shale materials, is shown. The results are important in particular for the Oil and Gas industry, for which the reduced strength properties (cohesion and friction angle) are critical for the success of drilling operations.
by Francois P. Ganneau.
S.M.
14
El-Zein, Mohamad Samih. "Strength in notched and impact damaged laminates." Diss., Virginia Polytechnic Institute and State University, 1989. http://hdl.handle.net/10919/54521.
Abstract:
The strength of notched and impact damaged laminates was studied. The solution for a plate containing an elliptic opening and inclusion was used as given by Lekhnitskii. The solution for the infinite plate, combined with laminate analysis to determine the ply stresses, and the average stress criterion proposed by Whitney and Nuismer were used to predict the notched strength. However, unlike Whitney and Nuismer, the average stress criterion was used at the ply level.
The strength of off-axis unidirectional laminates was predicted by using a matrix oriented failure criterion applied at a critical point on the boundary of the hole. A good agreement between the experimental and predicted data was obtained. On the other hand, an attempt made to predict the notched strength of angle-ply laminates was not as successful. This is believed to be due to the different failure modes existing among different [± 𝛉]s laminates.
The controversy on whether the characteristic dimension is a material or geometric property, together with the belief that the physics of fracture of composites is better represented at the ply level, have motivated the author to seek an invariant equation which describes the dependence of the characteristic dimension, D₀. A quantitative approach to determine the characteristic dimension in the average stress criterion was proposed. A good agreement between experimental and predicted data was found. It was also found that contrary to prior claims, the value of D₀ does not depend on the diameter of the hole, when used at the ply level. Moreover, the strength of quasi-isotropic laminates loaded at an angle ϕ with respect to the material x-axis was also studied. Again, excellent agreement between experiment and predictions was shown.
The tensile strength after impact (TSAI) was investigated. An approach based on modeling the delaminated area as an elliptic inclusion was used. The difference between the compliances of the plate and the inclusion was assumed to be proportional to the ratio of the delaminated areas. At low impact energy, a reference area was used. The results obtained using this approach gave good agreement with the experimental data.Ph. D.
15
Morata, Royes Joan. "Wear resistance of heat-treated Advanced High Strength Steels and casting." Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-80526.
Abstract:
The necessity to improve the durability of the machinery used in the milling industry has lead to several types of research. One study is focused on the plates that are located in the stationary and moving jaws of crushers to diminish particles sizes of Gneiss and Diabase rocks. Thus, one type of approach to increase its durability is by reducing the material loss of the plates. Amongst all the parameters to reduce the wear ratio that includes inputs from geometry to load, just the hardness input of the material can be in constant development. Consequently, there are two well-known types of heat treatment that can produce this change in hardness and are named Carbide Free Bainite (CFB) and Quenching and Partitioning (QP). In this master thesis the topic is to perform the QP heat treatments for two compositions A and B to obtain the microstructure of the steels that consist in a mix of austenite, bainite and martensite which considerably increase the hardness while the toughness is not drastically reduced due to the austenite soft phase. Five samples have been studied at four different partitioning temperatures: QP250 A, QP180 B, QP210 B, QP240 B and Mn Steel as it is the composition most used nowadays in the industry. In order to characterise both mechanical properties and microstructural features, different analysis had been performed with Micro-indentations, Charpy-V, Gouging Abrasion Tests, Optical Microscopy, Scanning Electron Microscopy and X-Ray Diffraction. These analysis had been done in the samples before and after wear as a result in change of the microstructure. As the abrasive-impact of the rocks collide with the sample, austenite transforms to martensite by induced plasticity called TRIP effect. Thus, the surface of the alloy is harder than the bulk material as no austenite is found and the wear ratio is seen to be improved. The results have shown several behaviours. Austenite transforms in its majority to fresh martensite which is an unstable martensitic phase but harder than tempered martensite that is the stable martensitic phase. Moreover, the difference in hardness between the bulk and the surface produce an affected depth layer as a consequence of the abrasive-impact penetration of rocks in which the microstructure has fully transformed to martensite on the surface and the austenite phase increases as it goes further inside the steel. The thinner this layer is, the better wear ratio presents the alloy. From all the samples, the best combination of hardness and toughness is for QP210 B.
16
Ibrahim, Wan Mohd Azhar Bin. "Strength parameters of some brittle dental materials : Weibull statistics." Thesis, University of Newcastle Upon Tyne, 1991. http://hdl.handle.net/10443/563.
Abstract:
There are many factors affecting the mechanical strength of a material. The effects of specimen size and strain rate (crosshead speed of testing) on the compressive, diametral tensile and flexural strengths some of the brittle dental materials are the main factors investigated in this study. The study was composed of two parts. The first part was to study the effect of specimen size and strain rate (crosshead speed of testing) on the compressive, diametral tensile and flexural strengths of a material tested. Weibull and Normal statistics were used to analyse the data. The analysis showed that specimen size and strain rate (crosshead speed of testing) affect the strength of a brittle materials. The optimum specimen size and crosshead speed of testing were determined for the compressive, diametral tensile and flexural tests. These specimen size and crosshead speed of testing are the 'test parameters'. The analysis also showed that the Weibull statistics was more adaptable method used in assessing the strength of a brittle materials. Therefore the value of Weibull modulus, characteristic strength and a stress at an arbitrary failure probability of 0.01 percent are the 'strength parameters' concluded from the analysis. In addition the relationship between Weibull modulus and deviation coefficient(%) and the relationship between deviation coefficient(%), mean strength and characteristic strength were established from the results of this investigation. A good correlation coefficient were obtained for these relationships. In the second parts of the study, 'strength parameters' some of brittle dental materials were determined by using the I test parameters If ound in the first -part' of the study. In addition the relationships found -in''the 'first part of the study were used, as -a model to estimate the 'strength parameter', from a-mean strength and and standard deviation of a small sample (a sample of 5 specimens). The results of this study showed --that a stress' at an arbitrary failure probability of 0.01 percent for' the small sample was not significantly varied from the stress at the same arbitrary failure probability of the large sample size.
17
Liao, Dongyi 1975. "Atomistic simulation of strength and deformation of ceramic materials." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/30003.
Abstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 2001.Includes bibliographical references (p. 203-216).
This thesis is a study of atomistic measures of strength and deformation of ceramic materials, utilizing molecular dynamics (MD) simulation that incorporates newly developed theoretical models and computational algorithms to probe the microstructural effects in crystalline, amorphous, and nanocrystalline media. Specific issues of a materials property or mechanics of materials nature are addressed in the context of characterizing the limits to strength and mechanisms of structural failure in two physically rather different model ceramics, SiO₂ described by pairwise ionic interactions and ZrC with many-body covalent interactions. These range from stress-strain responses to various applied loading, determination of fracture toughness, structural relaxation effects, to scaling with grain size. Additionally, a study of the thermal conductivity of ZrC is presented. On the computational side, thesis contributions consist of improved MD algorithms for finding neighbors and integrating the Newton's equations of motion, extension of Ewald summation to a binary ionic lattice for phonon dispersion, elastic constant, and heat current calculations, and a stand-alone scheme for coupled MD-continuum simulations based on domain decomposition and control feedback. The onset of structural instability in MD simulation of an initially defect-free lattice gives not only the theoretical or ideal strength of the deforming material, but also the mode of deformation and details of the structural defects nucleated afterwards. This provides a systematic basis for determining the effects of temperature on mechanical response, and stoichiometry effects in the case of carbon vacancies in ZrCl[sub]1-z.
(cont.) In tensile deformation of quartz, the structural transition from to β phase is observed and analyzed using a pseudo-critical phase transition model, leading to a new interpretation of the structure of the β-quartz. In uniaxial compression of α-quartz a local process of nucleation and growth of disordering is observed which appears to be distinct from the essentially homogeneous crystal-to-amorphous transformation that is well known to occur under hydrostatic compression. This finding also leads to a new interpretation of plastic deformation experiments. Fracture toughness is studied by introducing a pre-existing nanocrack in the simulations and following the details of crack tip extension under mode I loading. Simulations are shown to be quite consistent with the Griffith model in elementary fracture mechanics, confirming on the one hand the brittle nature of these two ceramics while also revealing the effects of surface relaxation, energy dissipation, and surface energy at the atomistic level. Similarly, simulations performed with initial structures with microstructural disorder, in the form of prepared amorphous and nanocrystalline specimens, also lead to new results pointing to the particular mechanisms, void nucleation and growth as well as strain-rate dependence in structural failure of an amorphous specimen, and grain-boundary sliding in shear deformation in very fine-grained nanocrystals. Taken together the thesis results demonstrate the feasibility and utility of the investigation of thermal and mechanical behavior of binary solids at the atomistic level ...
by Dongyi Liao.
Ph.D.
18
Choudhury, Ajmol H. "Structure, strength and defect characterisation of cement based materials." Thesis, Robert Gordon University, 2014. http://hdl.handle.net/10059/1031.
Abstract:
In cement based systems, the residual stresses are created by internal expansion. This provides toughening by the release of the residual stresses as the macro-crack propagates. While circumstantial evidence of the residual stresses exist (e.g. micro-crack formation leading to permanent deformation in flexural tests), it is very difficult to observe the mechanism in action. The quantitative estimate of the changes occurring in such cement-based systems is challenging due to the anisotropy and complexity of the material. Non-Destructive Testing (NDT) techniques were used in this research to observe the mechanism in action. An ultrasound technique is used to examine strength development and an acoustic emission (AE) technique is used to examine micro-structural changes, micro-cracks, crack initiation, crack propagation, crack arrests and crack bridging in plain concrete samples including samples containing admixtures and waste materials. The NDT techniques were found to be accurate in being able to measure compressive strength, with good correlation between both standard mechanical testing and NDT techniques. It was shown that admixtures could be effectively used to alter the properties of a curing cement mortar. This work has also demonstrated that ultrasound can be successfully used to determine the compressive strength of concrete from an early age. The ability to pre-determine the strength of concrete through correlation with NDT test parameters may reduce the time spent waiting on concrete to set and to obtain results using standard mechanical testing methods. The findings in this research present the effect admixtures had on the curing process of the cement based material. The introduction of certain additives into mortars have demonstrated an increase in both the rate of initial hardening and the magnitude of the compressive strength attained over the curing period depending on the mixture specification. The additives considered have been shown to actively alter and enhance the chemical process of curing from the start of hydration. Some additives that accelerate the curing process (accelerators) were found to lower the compressive strength of concrete using the ultrasound technique. Additives that caused an increase in the final strength of mortar also increased its toughness. The significant contributions in this research enabled observation of micro-structural changes and failure behaviour under compressive and flexural loading conditions on an on-line basis. The results obtained are encouraging and lead to increased understanding of cracking mechanisms in concrete containing various types of additives and aggregates. The application of the AE technique allowed the failure of interfacial bonding to be observed. The variation of the aggregate size and its effect on the monitored waveforms was established and the parameters in the AE signals are directly related to crack propagation (grain bridging/micro-mechanism) and strength of interfacial bonding. These findings have greatly contributed to the understanding of the concrete behaviour under complex conditions where no other technique could provide such valuable information on an online basis.
19
Cazamias, James Ulysses. "Characterizing the dynamic strength of materials for ballistic applications /." Full text (PDF) from UMI/Dissertation Abstracts International, 2000. http://wwwlib.umi.com/cr/utexas/fullcit?p3004229.
20
Wright, Wayne Clifton Augustus. "Blending of polyethylene materials for pipe applications." Thesis, Brunel University, 1989. http://bura.brunel.ac.uk/handle/2438/7120.
Abstract:
Melt blending of polyethylene, in particularly HDPE and LLDPE, have been shown to be a major success, especially in the film markets. In this thesis studies are reported on the stress rupture performance of pipes produced from selected polyethylene materials blended to a chosen MDPE pipe grade. The pipes were tested, notched or unnotched, at a single temperature of 80oC and at internal pressures designed to induce slit-mode failure. Results showed the simple concept of increasing the stress rupture performance of a pipe material by the addition of a higher molecular weight polymer was invalidated when applied to the blends system used in these studies. However molecular weight does have an influence to some degree as was illustrated by the addition of a very low molecular weight material, which produced the poorest stress rupture properties of the additives used. Charaterization techniques, including Differential Scanning Calorimetry and Dynamic Mechanical Thermal Analysis, showed good compatibility of the blends at all addition levels studied, illustrating that there was no seperation of the polyethylene phases. Fracture analysis of pipe failures showed variations between the blends, except for a MDPE additive which had similar molecular characteristics to the base resin. Some of the blends fracture surfaces were found to vary in fibre height and distribution from the bore region to the outside of the pipe. On the morphological front spherulites from pipe samples were found to be a poor indication of stress rupture behaviour. Pipe blends were produced which had fine/featureless morphologies but whose 80oC stress rupture behaviour was found to be good and poor in comparison to the control MDPE pipe resin which had a spherulitic structure much larger than all the blends studied. Models presented here infer that a number of mechanisms may be operating in producing these changes in stress rupture properties. One may be due to a dilution of a polyethylene system by materials of varying molecular weight and molecular weight distributions. This was evident in MDPE-AlMDPE-P blends (MDPE-P being a high molecular weight, low branch length additive), where the stress rupture performance initially decreased and then increased after addition levels of 10wt%. The main mechanisms for this system was postulated to be the initial dilution of octene branching levels within the MDPE-A blend causing a reduction in the ability of the branches to sterically hinder crack propagation under stress, to one of chain entanglement after sufficient levels of the additive was present in the blend to contribute to increasing the stress rupture behaviour. It was found that good blending can be produced using materials with similar branching types and distributions (especially in the high molecular weight tail), similar molecular weights and distributions and comparable crystallization temperatures.
21
Li, Hong. "Experimental micromechanics of composite buckling strength." Thesis, Georgia Institute of Technology, 1988. http://hdl.handle.net/1853/11719.
22
Du, Lianxiang. "Laboratory investigations of controlled low-strength material." Access restricted to users with UT Austin EID Full text (PDF) from UMI/Dissertation Abstracts International, 2001. http://wwwlib.umi.com/cr/utexas/fullcit?p3031045.
23
Edwards, Derek Oswald. "An investigation into possible means of increasing the strength of lightweight high strength concrete." Thesis, [Hong Kong] : University of Hong Kong, 1993. http://sunzi.lib.hku.hk/hkuto/record.jsp?B1331161X.
24
Olupot, Peter Wilberforce. "Assessment of ceramic raw materials in Uganda for electrical porcelain." Licentiate thesis, Stockholm : Royal Institute of Technology (KTH), 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4013.
25
張顯基 and Hin-kei Cheung. "Study on the strength of polymer melt." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1998. http://hub.hku.hk/bib/B31215087.
26
Cheung, Hin-kei. "Study on the strength of polymer melt /." Hong Kong : University of Hong Kong, 1998. http://sunzi.lib.hku.hk/hkuto/record.jsp?B19471415.
27
Asia, Winifred. "An in-vitro study of the physical properties of core build-up materials." University of the Western Cape, 2017. http://hdl.handle.net/11394/6307.
Abstract:
Magister Chirurgiae Dentium - MChD (Prosthodontics)The aim of this study was to evaluate and compare the physical properties of two core build-up materials (ParaCore and CoreXflow) and compare this to conventional composite material (Filtek Supreme Plus and SDR Flow) used as core build-up material.
28
Haidemenopoulos, Gregory N. "Dispersed-phase transformation toughening in ultrahigh-strength steels." Thesis, Massachusetts Institute of Technology, 1988. http://hdl.handle.net/1721.1/14564.
29
Gedeon, Steven Anthony. "Hydrogen assisted cracking of high strength steel welds." Thesis, Massachusetts Institute of Technology, 1987. http://hdl.handle.net/1721.1/14842.
30
Maguire, Dawn Laurel. "Failure mechanisms in VLSI bonds subjected to mechanical and environmental stresses." Thesis, Georgia Institute of Technology, 1986. http://hdl.handle.net/1853/30523.
31
Heying, Jamie John Gratton David G. "Flexural strength of interim fixed prosthesis materials after simulated function." [Iowa City, Iowa] : University of Iowa, 2009. http://ir.uiowa.edu/etd/377.
32
Fahad, M. K. "The strength of brittle materials under complex states of stress." Thesis, University of Newcastle Upon Tyne, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.315564.
33
Bouzalakos, Steve. "Controlled Low-Strength Materials Containing Solid Waste from Minerals Bioleaching." Thesis, Imperial College London, 2008. http://hdl.handle.net/10044/1/4265.
Abstract:
Sustainable treatment and disposal of mine waste is a serious environmental issue faced by the mining industry worldwide. Conventional methods of mine waste management predominantly involve indefinite retention in engineered tailings dams. The cost and liability of such surface storage facilities have increased significantly in recent years as an outcome of stringent environmental legislation and mine closure requirements gradually transforming the economics of mine waste disposal. Backfill methods, particularly cemented paste backfill, are increasingly perceived as sustainable, environmentally friendly and cost-effective alternatives as they put waste material to practical use. Controlled low-strength materials (CLSM) offer an effective and practical alternative to similar analogues - requiring minimal compaction, being self-levelling and excavatable in the future if necessary. The aim of this research was to develop and evaluate CLSM, previously un-tested at mines, in which novel utilisation of bioleach waste is maximised and Portland cement content minimised while satisfying performance requirements for classification as CLSM. Leachability of toxic substances was minimised through encapsulating CLSM within a coating of relatively inert CLSM. Formulation and optimisation of CLSM using statistical mixture design and response surface analysis has ensured proper understanding of component interactions and influence on mechanical strength with a minimum amount of experiments. Optimised CLSM formulations were tested for their mechanical, physical, micro-structural, mineralogical and chemical properties. Effects of encapsulation were determined by assessing chemical leaching. The work indicated that bioleach waste could be beneficially reformed as CLSM of appropriate compressive strength for application in groundwork as loadbearing materials. Porosity and hydraulic conductivity were correspondingly high. Leachability of arsenic, barium, chromium, lead and zinc was significant (levels varied depending on waste type). Encapsulation significantly reduced leachability indicating promising potential for implementation of this technology in the mining industry. The research presented in this thesis substantiated the need for, and potential of, sustainable novel alternative technologies such as CLSM to augment future waste management strategies in the mining industry via safe emplacement of solid bioleach waste in the sub-surface.
34
Hatzitheodorou, Alexandros. "In-situ strength development of concretes with supplementary cementitious materials." Thesis, University of Liverpool, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.441936.
35
Heying, Jamie John. "Flexural strength of interim fixed prosthesis materials after simulated function." Thesis, University of Iowa, 2009. https://ir.uiowa.edu/etd/377.
Abstract:
Statement of Problem
There are limited studies evaluating the effect of a cyclic load on interim fixed prosthetic materials and its effect on flexural strength.
Purpose of Study
1) To verify the flexural strength of previously studied interim fixed prosthetic materials.
2) To establish the flexural strength of new, advanced generation and untested interim fixed prosthetic materials.
3) To determine the effect of cyclic load on the flexural strength of interim fixed prosthetic materials.
Materials and Methods
Bar-type specimens of Caulk Temporary Bridge Resin, VitaVM CC, Protemp 3 Garant and Radica were fabricated according to International Standards Organization 4049 and American National Standards Institute/American Dental Association specification 27. After being stored in distilled water for 10 days, specimens were divided into Noncycled and Cycled Groups. The Noncycled Group specimens were fractured under a 3-point loading in a Bose Electroforce 3300 testing instrument at a crosshead speed of 0.75 mm/min. Cycled Groups specimens underwent a 6-12 Newton 3 Hertz cyclic load for 20,000 cycles in a Bose Electroforce 3300 testing instrument. Immediately following completion of the cycles, the specimens were fractured under a 3-point loading. Maximal loads to fracture in Newtons were recorded and mean flexural strengths were calculated (n = 20 per group). Comparisons were made with analysis of variance and Tukey's Multiple Comparison Test.
Results
Noncycled (NC) and Cycled (C) groups order of mean flexural strengths (MPa) from lowest to highest mean were as follows: Caulk (Noncycled - 53.83; C - 60.02), Vita VM CC (NC - 65.96; C - 66.83), Protemp 3 Garant (NC - 75.85; C - 77.18), and Radica (NC - 106.1; C - 115.96). In the Noncycled and Cycled groups, Radica was statistically superior when compared to all materials and Protemp 3 Garant was statistically superior to Caulk Temporary Bridge Resin. There was no statistically significant difference between the material's flexural strengths before and after cycles.
Conclusion
Within the limitations of this study, 20,000 cyclic loads of 6-12 Newtons at 3 Hertz did not have a significant effect on the flexural strength of interim fixed prosthetic materials. Radica demonstrated significantly superior flexural strength over other materials tested.
36
Hou, An. "Strength of composite lattice structures." Diss., Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/12475.
37
Schuetz, Daniel Philip. "Investigation of high strength stainless steel prestressing strands." Thesis, Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/47744.
Abstract:
Bridges and other coastal structures in Georgia and throughout the Southeast are deteriorating prematurely due to corrosion. Numerous corrosion
initiated failures have occurred in precast prestressed concrete (PSC) piles and reinforced concrete (RC) pile caps, leading to the costly repair and
replacement of either the entire bridge or the affected members. With the Federal Highway Administration's goal of a 100-year bridge service life
and recent legislative action such as the Bridge Life Extension Act, new emphasis has been placed on the development and implementation of new
corrosion mitigation techniques.
This thesis involves the mechanical testing, and proposed future test program of high-strength stainless steel (HSSS) prestressing strand to be used
in prestressed marine bridge piles. The metallurgy for two types of HSSS strand was selected from a previous study of the corrosion resistance,
mechanical properties, and feasibility of 6 candidate HSSS drawn wire samples. Duplex stainless steel (DSS) grades 2205 and 2304 were selected
for production of 7-wire 1/2" diameter prestressing strand. DSS wire rod was drawn, stranded, and heat-treated using the same production methods
and equipment as used for standard of practice, high carbon prestressing strand. The production process was documented to analyze the problems
facing this production method and suggest improvement and optimization.
After production, the strands were subjected to a series of mechanical tests. Tension testing was performed to provide a stress-strain curve for the
strands and related mechanical properties. Wire samples were also taken at varying points in the drawing process to give more information about
the work hardening of the stainless steels. Stress relaxation testing was performed on both strand and wire samples to assess the overall losses and
to provide comparisons between strand and wire test results as well as drawn wires before and after heat-treatment.
An experimental program for future study was designed to assess the HSSS prestressing strand behavior in precast piles. This testing involves
assessment of pile driving performance, pile flexural and shear behavior, strand transfer and development length, long-term prestressing force
losses, and material durability.
38
Ryan, Joanne Maureen. "Relating moisture ingress to component strength and stiffness for carbon-fibre composites." Thesis, Swansea University, 2011. https://cronfa.swan.ac.uk/Record/cronfa42389.
Abstract:
Moisture diffusion studies were performed using unidirectional (UD) tape and quasiisotropic (QI) woven 5-harness satin fabric, carbon fibre reinforced (CFR) epoxy composite materials. Firstly the moisture constants, (i.e. diffusion coefficient, D[x], and equilibrium moisture content, M[max]) were experimentally derived at 70°C and 85% relative humidity (%RH), for the two CFR materials. To investigate moisture absorption as a function of %RH test coupons were conditioned to differing equilibrium moisture levels viz., 70°C/60%RH, 70°C/75%RH, 70°C/85%RH, and 70°C/95%RH. Also oven dry (OD) and as-received (AR) tests were performed for baseline comparison. The effect of moisture absorption on the mechanical behaviour was investigated; lamina properties were studied by measuring tension, compression, shear (inter/intralaminar) strength and stiffness of the UD material. This comprehensive set of testing provided quantitative relationships between moisture content and mechanical properties. The quasi-isotropic lay-up was then utilised to investigate multi-directional laminate lay-ups using open hole tension and compression testing. The experimental data showed that the uptake of moisture in both the materials studied was described well by Fick's Second Law and the properties most affected by moisture ingress were matrix-dominated properties. More specifically, the transverse tensile strength, F[t][2] was most affected by the ingress of moisture, with a near 50% reduction in strength when conditioned to equilibrium moisture content at 70°C/95%RH. Such information is a necessary prerequisite if improved design procedures are going to be developed in the future. The initial phase of testing produced mechanical property/moisture relationships that were employed to predict the strength and stiffness of the material containing specific moisture gradients through-the-thickness (TTT). To be able to predict mechanical properties with different moisture distribution, firstly moisture distribution TTT of the material was modelled using an analytical solution to Fick's Second Law. Then moisture content was considered on a ply-by-ply basis TTT of the laminate; reductions were applied to each individual ply property dependent on the moisture content using the experimentally derived relationships, essentially applying environmental knock-down factors (KEKDF'S) to each individual ply. Classical Laminate Analysis (CLA) was then performed using the Max Stress failure criteria in order to predict the overall laminate failure. A second phase of mechanical testing was then performed to validate these predictions. The mechanical property predictions compared well to the experimental data showing similar reductions in strength for a given profile of moisture in the laminate. The predicted strengths also fell within the measured standard deviation of the experimental data in a significant proportion of the results.
39
Ericsson, Mats. "Fatigue Strength of Friction Stir Welded Joints in Aluminium." Doctoral thesis, Stockholm, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-160.
40
Yao, Jian. "High strength and high modulus electrospun nanofibres." Thesis, Queen Mary, University of London, 2014. http://qmro.qmul.ac.uk/xmlui/handle/123456789/9120.
Abstract:
In the last two decades, a rapidly growing polymer processing technology, electrospinning, has attracted great interests as it provides a viable and simple method to create ultra-fine continuous fibres. Despite the potential utilization of electrospun nanofibres in many fields, their success is limited so far due to their poor mechanical properties compared to corresponding textile fibres made from the same polymers, which is mainly ascribed to the low degree of orientation and chain extension of the macromolecules along the fibre axis in such fibres. In this thesis, first an in-depth review of the mechanical properties of electrospun fibres and recent developed methodologies to generate high strength and high modulus nanofibres will be presented. In the experimental work, electrospinning of rigid polymer PPTA was attempted and mechanical properties of obtained fibres were evaluated (Chapter 3). It was shown that the electrospinning process cannot be easily operated in a controllable and continuous manner although some high performance fibres were obtained. Chapter 4 dealt with the electrospinning of reactive mesogens (liquid crystal monomers) by employing polymers (PMMA and PA6) as matrix. The mechanical properties of the resulting composite nanofibres (PA6/RM257) showed dependence on the reactive mesogen (RM257) content and the phase separation between PA6 and RM257. In Chapter 5, a high performance polymer BPDA/PDA/ODA was synthesized and electrospun; the nanofibres were characterized using FTIR and WAXD and their mechanical tests were carried out based on unidirectional mats and multifilament bundles. A Weibull modulus based model was introduced to estimate the tensile strength of single nanofibres in such bundles. Subsequently, composites based on BPO nanofibres in a rubbery thermoplastic matrix were fabricated and evaluated in Chapter 7 using composite mechanics theories for off-axis properties and „Rule of Mixture‟ which were used to back-calculate the Young‟s modulus of single BPO nanofibres. From this it could be concluded that the developed co-polyimide BPO nanofibres exhibit among the highest mechanical properties of electrospun nanofibres reported in literature so far. It can be concluded that the electrospun BPO co-polyimide nanofibres and p-aramid fibres possess among the highest mechanical properties reported for electrospun fibres so far.
41
Konstantarakis, Christos. "Hydrogen degradation of high strength steel weldments." Thesis, Massachusetts Institute of Technology, 1993. http://hdl.handle.net/1721.1/47338.
Abstract:
Thesis (Ocean. E.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 1993, and Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Materials Science & Engineering, 1993.Includes bibliographical references (leaves 37-43).
by Christos Konstantarakis.
M.S.
Ocean.E.
42
Banna, Trinadha Rao. "The retentive strength of bonded amalgam restorations." Thesis, University of the Western Cape, 2005. http://hdl.handle.net/11394/2040.
Abstract:
Magister Scientiae - MScAmalgam bonding agents have been shown to enhance retention of amalgam restorations by mechanical means. However, recent studies showed that the use o glass ionomer cements and resin cements as lining and bonding materials to amalgam restorations will increase the retentive strength of the amalgam restorations, hence reducing the micro leakage and secondary caries. The purpose of this study was to compare the relative retentive strength of conventional amalgam restorations and bonded amalgam restorations using resin adhesive, glass ionomer cements and resin cements.
South Africa
43
Lee, Seunghun Marghitu Dan B. "Impacts of kinematic links with a granular material." Auburn, Ala., 2009. http://hdl.handle.net/10415/1751.
44
Cui, Guiyong. "Experimental study of the through-thickness strength of laminated composites." Thesis, University of Oxford, 1994. http://ora.ox.ac.uk/objects/uuid:80258f41-5358-447c-8047-0769c93f062c.
Abstract:
Complicated structures made of fibre reinforced laminates will suffer the failure of delamination which is the main through-thickness failure mode and is usually caused by the combined through-thickness stress state. Three tests, namely the oblique test, the waisted C-specimen test and the notched beam test, have been developed to reveal the failure activities under the combined stress state of in-plane normal stress, through-thickness normal stress and interlaminar shear, and, as a part of the big project, to establish a 3-D failure map in the coordinates of the three stress components. All tests have been analyzed either numerically by FEM or experimentally by Moire interferometry technique. The experimental results have shown that the failure behaviours of laminates are far more complicated than and very different from the traditional metallic materials which can usually be described by phenomenological failure criteria. The phenomenological criteria attempt has been tried and further confirmed that a full experimental understanding is the most important. Moreover, fractographic analysis by SEM has also been conducted to support the test results. Finally the Weibull statistics method has been used to treat the stress gradient effect in the different test geometries while establishing the failure map. It has proved to be a very efficient instrument.
45
Clarke, D. A. "The strength of model composites incorporating silicon carbide fibres." Thesis, University of Surrey, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.380359.
46
Owens, Anthony Taylor Tippur Hareesh V. "Development of a split Hopkinson tension bar for testing stress-strain response of particulate composites under high rates of loading." Auburn, Ala., 2007. http://repo.lib.auburn.edu/Send%2002-04-08/OWENS_ANTHONY_54.pdf.
47
Brach, Stella. "Strength properties of nanoporous materials : theoretical analyses and molecular dynamics computations." Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066618.
Abstract:
L’objectif principal de la thèse a été d’étudier les propriétés de résistance des matériaux nanoporeux par des approches théoriques et numériques. Dans le contexte des méthodes d’homogénéisation, des critères de résistance macroscopiques ont été établis par des approches analytiques à l’homogénéisation non-linéaire et à l’analyse limite. Les critères de résistance ainsi obtenus permettent de tenir en compte les effets de taille, tout en améliorant les formulations déjà existantes. En outre, dans le but de servir de référence pour la calibration et/ou la validation des modèles analytiques, des simulations numériques basées sur la dynamique moléculaire ont été conduites, en se référant à des monocristaux d’aluminium contenant des nanopores sphériques, sous des conditions multiaxiales de vitesse de déformation. Par rapport aux simulations actuellement disponibles dans la littérature, les résultats obtenus ont clairement établi que les surfaces de résistance sont significativement influencées par les trois invariants isotropes de contrainte. Finalement, dans le but de mettre à profit les indications fournies par les simulations numériques, le cas d’un matériau nanoporeux constitué d’une matrice ductile sensible aux trois invariants isotropes a été étudié par une approche par l’analyse limite, en prenant en compte une formulation modifiée du critère de résistance de bigoni. La solution exacte du problème a été établie dans le cas d’un chargement isotrope. A partir des résultats ainsi obtenus, une approche d’analyse limite cinématique a été mise en place, et permet de fournir des estimations des propriétés de résistance macroscopiques sous chargements axisymétriquesThe main objectif of the thesis consisted in investigating strength properties of nanoporous materials by means of theoretical and numerical approaches. In the framework of homogenization methods, novel macroscopic strength criteria have been established via a non-linear homogenization procedure and a kinematic limit-analysis approach. Resulting yield functions allowed to take into account void-size effects on nanoporous materials strength properties, thereby resulting in a strong enhancement of available estimates. Furthermore, aiming to funish effective benchmarking evidence for the calibration and/or the assessment of theoretical models, molecular-dynamics based computations have been carried out on in-silico single crystals embedding spherical nanovoids, simulation domains undergoing multiaxial strain-rate boundary conditions. With respect to available numerical studies, proposed results clearly showed the influence of all the three isotropic stress invariants on computed material strength surfaces. Finally, with the aim to account for physical indications coming from numerical simulations, a ductile nanoporous material with a general isotropic plastic matrix has been investigated via a limit analysis approach, by referring to a modified version of the bigoni strength criterion. The limit state of a hollow-sphere model undergoing isotropic loadings has been exactly determined. Correspondigly, a novel strength criterion has been analytically established in the case of axysimmetric boundary conditions
48
Caliskan, Ari Garo. "Micromechanics-based approach to predict strength and stiffness of composite materials." Thesis, This resource online, 1996. http://scholar.lib.vt.edu/theses/available/etd-09052009-041025/.
49
AHMAD, SAJJAD. "Innovative mix design of cementitious materials for enhancing strength and ductility." Doctoral thesis, Politecnico di Torino, 2015. http://hdl.handle.net/11583/2604771.
Abstract:
Cement based composites i.e. paste, mortar and concrete are the most utilized materials in the construction industry all over the world. Cement composites are quasi-brittle in nature and possess extremely low tensile strength as compared to their compressive strength. Due to their low tensile strength capacity, cracks develop in cementitious composites due to the drying shrinkage, plastic settlements and/or stress concentrations (due to external restrains and/or applied stresses) etc. These cracks developed at the nanoscale may grow rapidly due to the applied stresses and join together to form micro and macro cracks. The growth of cracks from nanoscale to micro and macro scale is very rapid and may lead to sudden failure of the cement composites. Therefore, it is necessary to develop such types of cement composites possessing higher resistance to crack growth, enhanced flexural strength and ductility.
The development of new technologies and materials has revolutionized every field of science by opening new horizons in production and manufacturing. In construction materials, especially in cement and concrete composites, the use of nano/micro particles and fibers in the mix design of these composites has opened new ways from improved mechanical properties to enhanced functionalities. Generally, the production or manufacturing processes of the nano/micro sized particles and fibers are energy intensive and expensive. Therefore, it is very important to explore new methods and procedures to develop less energy intensive, low cost and eco-friendly inert nano/micro sized particles for utilization in the cement composites to obtain better performance in terms of strength and ductility.
The main theme of the present research work was to develop a family of new type of cementitious composites possessing superior performance characteristics in terms of strength, ductility, fracture energy and crack growth pattern by incorporating micro sized inert carbonized particles in the mix design of cementitious composites. To achieve these objectives the micro sized inert carbonized particles were prepared from organic waste materials, namely: Bamboo, coconut shell and hemp hurds. For comparison purposes and performance optimization needs, another inorganic waste material named as carbon soot was also investigated in the present research.
The experimental investigations for the present study was carried out in two phases; In the first phase of research work, a methodology was developed for the synthesis of the micro sized inert carbonized particles from the above mentioned organic raw materials. In the second phase of research, various mix proportions of the cementitious composites were prepared incorporating the synthesized micro sized inert carbonized particles. For micro sized inert carbonized particles obtained from bamboo and coconut shell three wt.% additions i.e. 0.05, 0.08, 0.20 were investigated and for particles synthesized from hemp hurds 0.08, 0.20, 1.00 and 3.00 wt.% additions were explored.
The cement composites were characterized by third-point bending tests and their fracture parameters were evaluated. The mechanical characterization of specimens suggested that 0.08 wt.% addition of micro sized inert carbonized bamboo particles enhances the flexural strength and toughness of cement composites up to 66% and 103% respectively. The toughness indices I5, I10 and total toughness of the cement composites were also enhanced. The carbonized particles synthesized from coconut shell resulted in improved toughness and ductility without any increase in the modulus of rupture of the cement composite specimens. Maximum enhancements in I5 and I10 were observed for 0.08% addition of both carbonized and carbonized-annealed particles. For the carbonized hemp hurds cement composites the results indicate that the micro sized inert carbonized particles additions enhanced the flexural strength, compressive strength and the fracture energy of the cement composites.
The microstructure of the cement composites was also studied with the help of field emission scanning electron microscope (FESEM) by observing small chunks of cement composite paste samples. The FESEM observations indicated that the micro sized inert carbonized particles utilized in the mix design of these mixes were well dispersed in the cement matrix. It was also observed that the fracture paths followed by the cracks were tortures and irregular due the presence of micro particles in the matrix. The cracks during their growth often contoured around the inert particle inclusions and resulted in enhanced energy absorption capacity of the cement composites.
The study was further enhanced to the cement mortar composites and their performances were studied. The results indicated that the energy absorption behavior of the composites was enhanced for all the cement composites containing micro carbonized particles.
Finally, it is concluded that the ductility and toughness properties of the cement composites can be enhanced by incorporating the micro sized inert carbonized particles in the cement matrix. The fracture energy, ductility and toughness properties enhancement of the cement composites greatly depends upon the source and synthesis procedure followed for the production of micro sized inert carbonized particles.
50
Tomasino, Alfred P. "The effects of porosity on the out-of-plane tensile strength of laminated composites." Thesis, Virginia Polytechnic Institute and State University, 1988. http://hdl.handle.net/10919/53192.
Abstract:
The objective of this study was to investigate the out-of-plane tensile strength of graphite/epoxy laminates as a function of porosity. An experimental test program was designed to apply tension to the faces of circular graphite/epoxy specimens in a direction perpendicular to the laminate mid-plane. The specimens were removed from the webs of angle sections fabricated by Lockheed Georgia Company using (AS4/1806 and AS4/3501-6 graphite/epoxy material systems with a stacking sequence of (±45/90₂/ ±45/0₂)S or (±45/0₂/ +̅ 45/90₂)S. The specimen porosities were the result of four distinct processing methods: a baseline hand lay-up, low pressure cure-cycle, a solvent wipe of pre-preg to remove resin, and the addition of water between pre-pregs. The experimental results have shown a significant reduction in the out-of-plane tensile strength as a function of increasing void content.
The volume fraction of pores, pore geometry, size, and orientation were determined for a representative number of specimens by metallography and optical analysis methods. This data was combined with the out-of-plane tensile data and used in the theoretical model, prepared by Brown et al, to predict the out-of-plane strength as a function of porosity. The predicted strength values compared very well with the experimental data when the pores were found to be uniformly distributed throughout the laminate.Master of Science