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Pathan, Mehtab V., Borja Erice, Sathiskumar A. Ponnusami i Nik Petrinic. "Experimental characterisation of rate-dependent compression behaviour of fibre reinforced composites". EPJ Web of Conferences 183 (2018): 02053. http://dx.doi.org/10.1051/epjconf/201818302053.
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Fibre reinforced polymers (FRP) materials are being increasingly used for aerospace and automotive structural applications. One of the critical loading conditions for such applications is impact, consequently, understanding of the composite behavior under such loads becomes critical for structural design. The analysis and design process for achieving impact-resistant composite structures requires rate-dependent constitutive models, which, in turn, requires material properties of the composite over a range of strain rates. It is, therefore, the objective of the research to investigate the strain rate-dependent behavior of fiber reinforced composites under compressive loads for a wide range of fiber orientations. Quasi-static (≈ 1e-3 s−1) and high loading (≈ 200 s−1) rates are considered for the experimental study. Accordingly, two different test setups are utilized, a screw-driven universal testing machine for quasi-static tests and a Split Hopkinson Pressure Bar (SHPB) system for dynamic tests. The stress-strain response of the composite is reported for the different fiber orientations and the strain rates, revealing the rate-dependent characteristics of the carbon fiber reinforced composite. From the test results, it is observed that, the dependency of the fracture strength on the loading rate is significant. The results are summarised in terms of the failure envelope in the transverse compression-in-plane shear σ22 − σ12 plane for the two strain rates.
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Deshpande, V. M., i T. Chakraborty. "Dynamic compressive behaviour of Rewa shale through SHPB tests". IOP Conference Series: Earth and Environmental Science 1124, nr 1 (1.01.2023): 012042. http://dx.doi.org/10.1088/1755-1315/1124/1/012042.
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Abstract The present work investigates the high strain rate behaviour of transversely isotropic Rewa shale using a split Hopkinson pressure bar. Rewa shale, a type of Vindhyan shale, is collected from Rewa district in the Madhya Pradesh state of India. Samples are loaded at various strain rates ranging from 110/s to 874/s. It is found that the compressive strength is rate-dependent, and it increases as the strain rate rises. The highest compressive strength is exhibited by samples at 0° and 90°. Samples at 30°, 45° and 60° fail at higher strains and strain rates. All samples subjected to dynamic compressive loading are pervasively fragmented. The results can potentially be applied to improve drilling and blasting operations.
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Takiguchi, M., S. Izumi i F. Yoshida. "Rate-dependent shear deformation of ductile acrylic adhesive and its constitutive modelling". Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 218, nr 6 (czerwiec 2004): 623–29. http://dx.doi.org/10.1243/095440604774202268.
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Recently, new types of structural adhesive with high ductility, as well as high strength, have been developed and put on the market. Such high ductile adhesives usually have strong rate sensitivity in their flow stress. In order to investigate the rate-dependent deformation behaviour of an acrylic adhesive, tensile lap shear tests were performed at various crosshead speeds at room temperature. Stress relaxation tests were also performed. In the tensile lap shear tests, it was found that the shear flow stress of the adhesive resin increased remarkably with increasing shearing speed. In the stress relaxation tests, the stress decreased rapidly at the early stage, and it gradually approached an asymptotic stress value. In order to describe such rate-dependent deformation characteristics of adhesive resin, a viscoplastic constitutive model is presented in this paper. The shear stress-strain responses, as well as stress relaxation behaviour, predicted by the present model agree well with the corresponding experimental results.
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Çelen, S., i K. Kahveci. "Microwave drying behaviour of tomato slices". Czech Journal of Food Sciences 31, No. 2 (18.04.2013): 132–38. http://dx.doi.org/10.17221/30/2012-cjfs.
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The microwave drying behaviour of tomato slices was investigated experimentally to determine the effects of microwave power on the drying rate, energy consumption, and dried product quality in terms of colour, and a theoretical model was proposed to define the drying curves of tomato slices. The experiments performed with the microwave power of 90, 180, 360, and 600 W indicate that the drying time and the energy consumption decreased considerably with an increase in microwave power. The experiments also revealed that the drying rate shows first an increase and then a decrease during drying, and that the colour quality of the product deteriorates significantly with the increase of the microwave power. A theoretical model was developed using the solution of energy equation considering the microwave power as an internal heat source. The electric field strength inside the material was assumed to be dependent on the moisture content and the constants emerging from this assumption were obtained by minimising the sum of squared differences between the theoretical results and experimental data obtained for various drying conditions. The results show that the values proposed for the constants provide a good agreement between the theoretical and experimental drying behaviour.
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Maqsood, Zain, Junichi Koseki i Hiroyuki Kyokawa. "Effects of loading rate on strength and deformation characteristics of gypsum mixed sand". E3S Web of Conferences 92 (2019): 05008. http://dx.doi.org/10.1051/e3sconf/20199205008.
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It has been unanimously acknowledged that the strength and deformation characteristics of bounded geomaterials, viz. cemented soils and natural rocks, are predominantly governed by the rate of loading/deformation. Rational evaluation of these time-dependent characteristics due to viscosity and ageing are vital for the reliable constitutive modelling. In order to study the effects of ageing and loading/strain rate (viscosity) on the behaviour of bounded geomaterials, a number of unconfined monotonic loading tests were performed on Gypsum Mixed Sand (GMS) specimens at a wide range of axial strain rates; ranging from 1.9E-05 to 5.3E+00 %/min (27,000 folds), and at different curing periods. The results indicate shifts in the viscous behaviour of GMS at critical strain rates of 2.0E-03 and 5.0E-01 %/min. In the light of this finding, the results are categorized into three discrete zones of strain rates, and the behaviour of GMS in each of these zones is discussed. A significant dependency of peak strength and stress-strain responses on strain rate was witnessed for specimens subjected to strain rates lesser than 2.0E-03 %/min, and the effects of viscosity/strain rate was found to be insignificant at strain rate higher than 5.0E-01%/min.
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Kim, Jang-Kyo, Man-Lung Sham, Min-Seok Sohn i Shisheng Hu. "Effects of Fibre Surface Treatment on Dynamic Tensile Properties of Glass Woven Fabric Reinforced Vinylester Composites". Polymers and Polymer Composites 13, nr 5 (lipiec 2005): 453–66. http://dx.doi.org/10.1177/096739110501300503.
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Glass fibre has been recognized as a strain rate dependent material. Its failure behaviour changes from brittle to ductile as the strain rate increases. As a consequence, the strength of the glass fibre increases, but the fibres within a composite become more prone to debond from the matrix because of the brittleness of the matrix material, promoted by the high strain rate. In the present study, the tensile responses of glass woven fabric reinforced vinyl ester composites with various fibre surface treatments are examined under static and dynamic loading conditions. The results show that both the ductility and the strength of the composites increased with increasing strain rate. The tensile strength was lower and the failure strain was higher in the weft direction than in the warp direction, because of excessive crimping in the former direction. The tensile strength in general increased with increasing silane concentration, for the majority of strain rates studied. The influence of fibre surface treatment on the impact tensile strength and modulus of composites were functionally similar, confirming the influence of fibre-matrix interphase properties on composite fracture behaviour at high strain rates.
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Nashed, Nour, Stephanie Chan, Matthew Lam, Taravat Ghafourian i Ali Nokhodchi. "Effect of pH, Ionic Strength and Agitation Rate on Dissolution Behaviour of 3D-Printed Tablets, Tablets Prepared from Ground Hot-Melt Extruded Filaments and Physical Mixtures". Biomedicines 11, nr 2 (27.01.2023): 375. http://dx.doi.org/10.3390/biomedicines11020375.
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With the current focus on 3D-printing technologies, it is essential to understand the processes involved in such printing methods and approaches to minimize the variability in dissolution behaviour to achieve better quality control outcomes. For this purpose, two formulations of theophylline tablets were prepared using hydroxypropyl cellulose (HPC) and ethyl cellulose (EC). Among the two types of tablets, three different methods (physical mixture (PM), hot-melt extrusion (HME) and 3D-printing fused deposition modelling (FDM)) were applied and their dissolution behaviours were studied under various conditions using a biodissolution tester. This was carried out at pH values of 1.2, 2.2, 5.8, 6.8, 7.2 and 7.5, mimicking the medium in the gastrointestinal tract. Dissolution tests under two dipping rates (10 dpm and 20 dpm) and two ionic strengths (0.2 M and 0.4 M) were conducted to mimic fed and fasting conditions. The dissolution efficiency (DE%), release rate, similarity factor (f2) and difference factor (f1) were calculated. When comparing the DE%, the formulation containing EC showed less sensitivity to changes in the dipping rate and ionic strength compared to the HPC formulation. As for the manufacturing method, 3D-printing FDM could improve the robustness of the dissolution behaviour of both formulations to dipping rate changes. However, for ionic strength changes, the effect of the manufacturing method was dependent on the formulation composition. For example, the 3D-printed tablets of the HPC formulation were more sensitive to changes in ionic strength compared to the EC-containing formulation. The release mechanism also changed after the thermal process, where n values in the Korsmeyer–Peppas model were much higher in the printing and HME methods compared to the PM. Based on the formulation composition, the 3D-printing method could be a good candidate method for tablets with a robust dissolution behaviour in the GI tract. Compared to HPC polymers, using hydrophobic EC polymers in printable formulations can result in a more robust dissolution behaviour in fed and fasting states.
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Li, Xueyang, Christian C. Roth i Dirk Mohr. "Large Deformation Behavior of High Strength Steel Under Extreme Loading Conditions: High Temperature and High Strain Rate Experiments and Modeling". EPJ Web of Conferences 183 (2018): 01053. http://dx.doi.org/10.1051/epjconf/201818301053.
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Plasticity and fracture experiments are carried out on flat smooth and notched tensile specimens extracted from DP800 steel sheets. A split Hopkinson pressure bar testing system equipped with a load inversion device is utilized to reach high strain rates. Temperature dependent experiments ranging from 20°C to 300°C are performed at quasi-static strain rates. The material exposes a monotonic strain hardening behaviour with a non-monotonic temperature dependency. The rate-independent material behaviour at room-temperature is described with a non-associated Hill’48 plasticity model and an Swift-Voce strain hardening. A machine learning based model is used multiplicatively to capture the rate and temperature responses. A good agreement between measured and simulated force-displacement curves as well as local surface is obtained. The loading paths to fracture are then extracted to facilitate further development of a temperature dependent fracture initiation model.
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Yin, Jian-Hua, i James Graham. "Elastic viscoplastic modelling of the time-dependent stress-strain behaviour of soils". Canadian Geotechnical Journal 36, nr 4 (22.11.1999): 736–45. http://dx.doi.org/10.1139/t99-042.
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This paper presents a new framework for elastic viscoplastic (EVP) constitutive modelling. In developing the model, a general one-dimensional elastic viscoplastic (1D EVP) relationship is first derived for isotropic stressing conditions using an "equivalent-time" concept. This 1D EVP model is then generalized into a three-dimensional EVP model based on Modified Cam-Clay and viscoplasticity. Fitting functions are proposed for fitting data when model parameters are being determined. Using these functions, a specific EVP model is developed which describes the time-dependent stress-strain behaviour of soils under triaxial stress states. This model has been calibrated using data from a densely compacted sand-bentonite mixture. The calibrated model is used to compute time-dependent (or strain rate dependent) stress-strain curves from a multistage shear creep test and a step-changed, constant strain rate undrained triaxial compression test. Predictions from the EVP model are in general agreement with measured values. It is demonstrated that the model can simulate accelerating creep when deviator stresses are close to the shear strength envelope in a q creep test. It can also model the behaviour in unloading-reloading and relaxation. Limitations and possible improvements are also indicated.Key words: equivalent time, stress-strain, time dependent, elastic, viscoplastic, triaxial.
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Banerjee, Amborish, B. Gangadhara Prusty i Saroj Bhattacharyya. "Rate-dependent mechanical strength and flow behaviour of dual-phase high carbon steel at elevated temperatures: An experimental investigation". Materials Science and Engineering: A 744 (styczeń 2019): 224–34. http://dx.doi.org/10.1016/j.msea.2018.12.002.
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Staszewska, Katarzyna, i Marcin Cudny. "Modelling the time-dependent behaviour of soft soils". Studia Geotechnica et Mechanica 42, nr 2 (30.06.2020): 97–110. http://dx.doi.org/10.2478/sgem-2019-0034.
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AbstractTime dependence of soft soils has already been thoroughly investigated. The knowledge on creep and relaxation phenomena is generally available in the literature. However, it is still rarely applied in practice. Regarding the organic soils, geotechnical engineers mostly base their calculations on the simple assumptions. Yet, as presented within this article, the rate-dependent behaviour of soft soils is a very special and important feature. It influences both the strength and the stiffness of a soil depending on time. It is, thus, significant to account for time dependence in the geotechnical design when considering the soft soils. This can result in a more robust and economic design of geotechnical structures. Hence, the up-to-date possibilities of regarding creep in practice, which are provided by the existing theories, are reviewed herein.In this article, we first justify the importance of creep effects in practical applications. Next, we present the fundamental theories explaining the time-dependent behaviour of organic soils. Finally, the revision of the existing constitutive models that can be used in numerical simulations involving soft soils is introduced. Both the models that are implemented in the commercial geotechnical software and some more advanced models that take into account further aspects of soft soils behaviour are revised. The assumptions, the basic equations along with the advantages and the drawbacks of the considered models are described.
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Koutek, Bohumír, Lubomír Musil, Jiří Velek i Milan Souček. "Fluorescence behaviour of some 4-substituted halobenzenes". Collection of Czechoslovak Chemical Communications 50, nr 8 (1985): 1753–63. http://dx.doi.org/10.1135/cccc19851753.
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The fluorescence characteristics of 4-substituted chloro and fluorobenzenes I and II were studied in isooctane and acetonitrile solutions. It was found that all compounds exhibit a weak (substituent and solvent dependent) fluorescence in the range 305-370 nm with quantum yields 1.2 . 10-2-2.3 . 10-1. The relation between the substituent nature and fluorescence band position may be quantified by log νf~ = ρσp + log νf~0, the magnitude of the shift paralleling the donor strength of the substituent. Fluorescence quantum yields are increased approximately by a factor 2 on going from isooctane to acetonitrile and solvent-induced shifts are proportional to the static dipole moment change Δμ which occurs upon excitation. Radiative decay rate varies only slightly around a mean value of 5 . 107 s-1 and shows no substantial difference between chloro (I) and fluoro (II) derivatives. The non-radiative decay rate (of the order ~ 109 s-1) was found to be about 5 times higher in the case of chloro compounds due to the more efficient S1 - Tn intersystem crossing.
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Qin, Jin Gui, Fang Yun Lu, Yu Liang Lin i Xue Jun Wen. "Effect of Loading Rate on Tensile Properties of Automotive Steel Sheet". Advanced Materials Research 690-693 (maj 2013): 211–17. http://dx.doi.org/10.4028/www.scientific.net/amr.690-693.211.
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Results of uni-axial tensile loading of three automotive steels at different strain rates (0.0011–3200s-1) are reported here. Quasi-static tensile tests were performed under the strain rate of 1.1×10-3 s-1 using an electromechanical universal testing machine, whereas dynamic tests were carried out under the strain rate in the range of 1100 to 3200 s-1 using a Split Hopkinson Tensile Bar apparatus. Based on the experimental results, the material parameters of widely used Johnson–Cook model which described the strain rate and temperature-dependent of mechanical behaviour were determined. The experiments show that strain-rate hardening is superior to thermal softening: yield stresses, tensile strength, deformation, and energy dissipation increase with the strain rate from quasi-static tests to dynamic tests. The Johnson–Cook model can describe the behaviour of these steels and provides the opportunity to study the material and structural response.
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Çetin, Melik. "Abrasive wear behaviour of cast Al–Si–Mn alloys". Proceedings of the Institution of Mechanical Engineers, Part E: Journal of Process Mechanical Engineering 233, nr 4 (17.12.2018): 908–18. http://dx.doi.org/10.1177/0954408918818735.
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In this paper, the effect of manganese (wt%) and size of the Al2O3 abrasive grains of abrasive wear behaviours of Al–Si–(0.16–0.76%) Mn alloy was examined. Abrasive wear experiments were conducted against abrasive Al2O3 paper grains with diameters in the variety of 38–250 µm, under the normal load range of 10, 20 and 30 N and the sliding velocity of 0.1 m s−1. Wear measurements have shown that the wear rate of the material is dependent on the manganese content and the abrasive grain size. The best wear resistance is in the content of 0.73 Mn, which is associated with increased toughness and strength. The Al–Si casting alloy which had 0.73% Mn content exhibited lower wear rate than the Al–Si–0.16/0.22/0.23% Mn alloys after scoured on fine abrasive Al2O3 grains (<65 µm). Wear experiments achieved on Al2O3 grains having sizes greater than 65 µm revealed that, the cast Al–Si– alloy which had 0.73% Mn content had lower wear rate than the cast Al–Si–0.16/0.22/0.23% Mn alloys.
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Toribio, Jesús, Beatriz González i Juan Carlos Matos. "Transient and Steady State Regimes of Fatigue Crack Growth in High Strength Steel". Key Engineering Materials 525-526 (listopad 2012): 553–56. http://dx.doi.org/10.4028/www.scientific.net/kem.525-526.553.
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This paper analyzes the propagation of fatigue cracks in pearlitic steel in two forms, hot rolled bar and cold drawn wire. The experimental procedure consisted of fatigue tests on bars under tensile loading, using steps with decreasing amplitude of stress and constant stress range during each step. The curves plotting cyclic crack growth rate versus stress intensity factor range show a main steady-state regime preceded by transient paths. The steady-state regime is associated with the curves of the Paris regime. The cold drawing process improves the fatigue behaviour of steel by retarding the cyclic crack growth rate, and the propagation rate is not dependent on theR-ratio. The transient branches allow one to calculate the plastic zone size, considering that they are a consequence of the overload retardation effect at each step change, and a unique expression is fitted as a function ofKmaxΔKproduct and of the conventional mechanical properties.
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Yeakel, Justin D., Jean P. Gibert, Thilo Gross, Peter A. H. Westley i Jonathan W. Moore. "Eco-evolutionary dynamics, density-dependent dispersal and collective behaviour: implications for salmon metapopulation robustness". Philosophical Transactions of the Royal Society B: Biological Sciences 373, nr 1746 (26.03.2018): 20170018. http://dx.doi.org/10.1098/rstb.2017.0018.
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The spatial dispersal of individuals plays an important role in the dynamics of populations, and is central to metapopulation theory. Dispersal provides connections within metapopulations, promoting demographic and evolutionary rescue, but may also introduce maladapted individuals, potentially lowering the fitness of recipient populations through introgression of heritable traits. To explore this dual nature of dispersal, we modify a well-established eco-evolutionary model of two locally adapted populations and their associated mean trait values, to examine recruiting salmon populations that are connected by density-dependent dispersal, consistent with collective migratory behaviour that promotes navigation. When the strength of collective behaviour is weak such that straying is effectively constant, we show that a low level of straying is associated with the highest gains in metapopulation robustness and that high straying serves to erode robustness. Moreover, we find that as the strength of collective behaviour increases, metapopulation robustness is enhanced, but this relationship depends on the rate at which individuals stray. Specifically, strong collective behaviour increases the presence of hidden low-density basins of attraction, which may serve to trap disturbed populations, and this is exacerbated by increased habitat heterogeneity. Taken as a whole, our findings suggest that density-dependent straying and collective migratory behaviour may help metapopulations, such as in salmon, thrive in dynamic landscapes. Given the pervasive eco-evolutionary impacts of dispersal on metapopulations, these findings have important ramifications for the conservation of salmon metapopulations facing both natural and anthropogenic contemporary disturbances. This article is part of the theme issue ‘Collective movement ecology’.
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Ferreira, Fernanda Bessa, Paulo M. Pereira, Castorina Silva Vieira i Maria de Lurdes Lopes. "Time-Dependent Response of a Recycled C&D Material-Geotextile Interface under Direct Shear Mode". Materials 14, nr 11 (4.06.2021): 3070. http://dx.doi.org/10.3390/ma14113070.
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Geosynthetic-reinforced soil structures have been used extensively in recent decades due to their significant advantages over more conventional earth retaining structures, including the cost-effectiveness, reduced construction time, and possibility of using locally-available lower quality soils and/or waste materials, such as recycled construction and demolition (C&D) wastes. The time-dependent shear behaviour at the interfaces between the geosynthetic and the backfill is an important factor affecting the overall long-term performance of such structures, and thereby should be properly understood. In this study, an innovative multistage direct shear test procedure is introduced to characterise the time-dependent response of the interface between a high-strength geotextile and a recycled C&D material. After a prescribed shear displacement is reached, the shear box is kept stationary for a specific period of time, after which the test proceeds again, at a constant displacement rate, until the peak and large-displacement shear strengths are mobilised. The shear stress-shear displacement curves from the proposed multistage tests exhibited a progressive decrease in shear stress with time (stress relaxation) during the period in which the shear box was restrained from any movement, which was more pronounced under lower normal stress values. Regardless of the prior interface shear displacement and duration of the stress relaxation stage, the peak and residual shear strength parameters of the C&D material-geotextile interface remained similar to those obtained from the conventional (benchmark) tests carried out under constant displacement rate.
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Lee, W.-S., i T.-H. Chen. "Plastic deformation and fracture characteristics of Hadfield steel subjected to high-velocity impact loading". Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 216, nr 10 (1.10.2002): 971–82. http://dx.doi.org/10.1243/095440602760400940.
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Investigation of the impact behaviour of Hadfield steel has been carried out in a broad range of strain rates from 10−3 to 9 × 103s−1 by means of a servo-hydraulic machine and a compressive split Hopkinson bar. The effects of strain rate on the impact properties, substructure evolution and fracture resistance have been evaluated. The observed stress-strain response is influenced greatly by strain rate, resulting in obvious changes of work hardening rate, strain rate sensitivity and activation volume. This rate-dependent behaviour is in good agreement with model predictions using the Zerilli-Armstrong constitutive law. Dislocation tangle and deformation twin substructures are also found to develop as a function of strain rate. Increasing dislocation and twin densities enhance the work hardening rate and flow strength. Catastrophic failure at high rates results from the formation of localized shear bands. With increasing strain rate, there is an increase in brittle cleavage microfracture, resulting in ductility loss. Microcracking initiates at grain boundaries due to the presence of carbide precipitates.
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Ji, Min-Ki, Min-Su Lee, Yong-Taek Hyun i Tea-Sung Jun. "Effects of strain rate on tensile deformation behaviour in Ti-6Al-4V at cryogenic temperature". MATEC Web of Conferences 321 (2020): 06010. http://dx.doi.org/10.1051/matecconf/202032106010.
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In this study, we investigated the effects of strain rate on tensile deformation behaviour in Ti-6Al-4V sheet at cryogenic temperature. X-ray diffraction (XRD) was used to identify the crystallographic orientation of rolled Ti-6Al-4V. A series of tensile tests were performed by constant strain rate method (CRS) with variable strain rates (i.e., on the order of 1x10-2 to 10-4•s-1). Liquid nitrogen (LN2) was used to mimic cryogenic environment, and for the thermal equilibrium the specimens were immersed in the vessel containing liquid nitrogen for ~10 minutes before tensile testing, and the temperature condition was continuously maintained during the testing. Microstructure and fracture surface was analysed by polarised light microscopy and scanning electron microscope (SEM). Electron backscatter diffraction (EBSD) was further used to characterise local deformation behaviour. Deformation twinning is occurred at cryogenic tempearture, which is rather different to the deformation at room temperature. It is thought that the twinning induced deformation behaviour may lead to a strength enhancement and a rate dependent ductility improvement. Key words: Ti-6Al-4V, cryogenic, microstructure, deformation twinning, EBSD
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Hinchberger, S., J. Weck i T. Newson. "Mechanical and hydraulic characterization of plastic concrete for seepage cut-off walls". Canadian Geotechnical Journal 47, nr 4 (kwiecień 2010): 461–71. http://dx.doi.org/10.1139/t09-103.
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This paper describes a series of laboratory tests performed to characterize the mechanical and hydraulic properties of plastic concrete (PL-C). PL-C is used in the construction of seepage cut-off walls in dams and it comprises cement, aggregate, and water mixed with sodium bentonite. The addition of sodium bentonite causes a reduction in strength and improved ductility after failure compared with normal concrete. The mechanical properties of PL-C are studied using a series of unconfined compression tests and confined compression tests performed while simultaneously permeating water through PL-C specimens. Stress relaxation and controlled rate of loading tests are also performed to investigate the rate-sensitivity and time-dependency of plastic concrete. The test results show that the hydraulic conductivity of PL-C increases between two and three orders of magnitude during triaxial compression due to yielding, crack formation, and dilation of the cracks. Such changes in the behaviour of PL-C should be minimized during design by controlling the working strains and using erosion-resistant mixes. In addition to these findings, PL-C exhibits significant time-dependent behaviour similar to that observed for clays, and the variation of compressive strength versus confining stress is comparable to normal strength concrete.
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Bakalarz, M., i P. G. Kossakowski. "Preliminary assessment of the bending strength of mid-nineteenth century oak timber". Advances in Materials Science 17, nr 1 (1.03.2017): 58–69. http://dx.doi.org/10.1515/adms-2017-0005.
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Abstract This paper deals with results of preliminary analysis to determine the bending strength of approximately 150 year old oak timber obtained from structural elements used in construction. The test procedures were those specified in the PN-EN 408 standard. The experiments involved subjecting specimens to four-point static loading using three different loading rates: 5, 7 and 10 mm/min. The specimens were sampled from full-size timber beams. The experimental data revealed that after such a long period of use the structural oak timber elements had retained high strength. The failure mode and the behaviour of the beams during tests were dependent on the location of wood defects as well as the rate of deflection gain in time.
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Wang, Hongxu, Paul J. Hazell, Krishna Shankar, Evgeny V. Morozov, Zlatko Jovanoski, Andrew D. Brown, Zongjun Li i Juan P. Escobedo-Diaz. "Tensile properties of ultra-high-molecular-weight polyethylene single yarns at different strain rates". Journal of Composite Materials 54, nr 11 (22.10.2019): 1453–66. http://dx.doi.org/10.1177/0021998319883416.
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This paper presents the details of experimental work on characterising the tensile properties of UHMWPE (Spectra® 1000) single yarns at different strain rates from 3.3 × 10−5 to 400/s. According to the measured stress–strain curves, there was a transition from ductile to brittle behaviour as the strain rate increased from 3.3 × 10−5 to 0.33/s; the tensile properties were highly sensitive to strain rate in this range. Specifically, the tensile strength and Young’s modulus increased distinctly with increasing strain rate while the failure strain and toughness decreased. However, these tensile properties were not dependent on strain rate over the range from 0.33 to 400/s. The results showed that the measured tensile strength, failure strain and Young’s modulus were independent of the tested gauge lengths (25 and 50 mm). Moreover, yarn type (warp and weft) had a noticeable effect on tensile strength, but the effect of yarn type on failure strain and Young’s modulus was negligible. The microscopic examination of fractured fibres’ ends revealed that fibrillation and axial splitting were the dominant fracture modes at low strain rates, while the fibres failed in a more brittle manner with little fibrillation at high strain rates.
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Li, Dan, Ruilin You i Sakdirat Kaewunruen. "Crack Propagation Assessment of Time-Dependent Concrete Degradation of Prestressed Concrete Sleepers". Sustainability 14, nr 6 (9.03.2022): 3217. http://dx.doi.org/10.3390/su14063217.
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As prestressed concrete sleepers are continuously exposed to various environmental and loading conditions, it is increasingly crucial to analyse their current and future serviceability performance. In practice, the main cause of cracking in prestressed concrete sleepers is usually induced by impact loads. The most heavily influenced sections are the midspan and rail-seat area of sleepers. This paper investigates the effects of time-dependent concrete strength degradation on the capacity of prestressed concrete sleepers. The factors affecting concrete strength degradation are analysed in order to evaluate the crack behaviour of prestressed concrete sleepers. A finite element modelling approach is developed for prestressed concrete sleepers, which is used to assess the effects of structural behaviour in railway sleepers. The sleeper model has been calibrated and validated. This research firstly discusses time-dependent behaviour using load–crack length responses. It is shown that various cracking modes cause an overall increase in the maximum cracking length as prestressed concrete sleepers age. This paper demonstrates that initial cracking loads and ultimate crack lengths have significant change in first 20 years. After 40 years of service life, the crack resistance of prestressed concrete sleepers becomes very weak which is only 61.32% of the new sleeper. In long term, the initial cracking load keeps reducing, and the crack propagation rate becomes sharp. The presented methodology and results can greatly assist in decision-making for the repair or replacement of prestressed concrete sleepers and aid in the design of new prestressed concrete sleepers considering their future performance.
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Santos, F. L. Gea dos, i J. L. A. O. Sousa. "Determination of parameters of a viscous-cohesive fracture model by inverse analysis". Revista IBRACON de Estruturas e Materiais 8, nr 5 (październik 2015): 669–706. http://dx.doi.org/10.1590/s1983-41952015000500007.
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ABSTRACTThe quasi-brittle, loading rate dependent behaviour of the concrete, characterized by a fracture process zone (FPZ) ahead of the crack front, can be described through a viscous-cohesive model. In this paper, a viscous cohesive model proposed in a former paper is evaluated for a group of high strength concrete beams loaded at rates from 10-5 mm/s to 10+1 mm/s. A software has been developed to enable the automatic determination of the viscous-cohesive model parameters through inverse analysis on load-versus loading-point displacement (P-d) from threepoint bend tests on notched prismatic specimens. The strategy allowed the sensitivity analysis of the parameters related to viscous behaviour. The analysis of results shows that the formerly proposed model can be improved for a better simulation of the loading rate dependence on the cohesive fracture process.
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Rossi, Pierre. "Influence of the Loading Rate on the Cracking Process of Concrete in Quasi-Static Loading Domain". CivilEng 4, nr 1 (26.12.2022): 1–11. http://dx.doi.org/10.3390/civileng4010001.
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This study presents analysis of two types of experimental test related to the crack propagation in concrete specimens subjected to high-sustained loading levels and quasi-static loadings. The concept of the equivalent crack length is introduced to perform this analysis. Even though this analysis is partial, it shows the influence of loading rate conditions on the crack process rate. This result shows that, in the domains of low and very low loading rates, the concrete mechanical characteristics linked to the cracking process (for example, tensile strength, post-cracking behaviour, etc.) are dependent on the loading rates applied to the specimens for determining them.
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Kelln, Curtis, Jitendra Sharma, David Hughes i James Graham. "An improved elastic–viscoplastic soil model". Canadian Geotechnical Journal 45, nr 10 (październik 2008): 1356–76. http://dx.doi.org/10.1139/t08-057.
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This paper develops an improved and accessible framework for modelling time-dependent behaviour of soils using the concepts of elasticity and viscoplasticity. The mathematical description of viscoplastic straining is formulated based on a purely viscoplastic and measurable phenomenon, namely creep. The resulting expression for the viscoplastic strain rates includes a measure of both effective stress and the corresponding volumetric packing of the soil particles. In this way, the model differs from some earlier viscoplastic models and arguably provides a better conceptual description of time-dependent behaviour. Analytical solutions are developed for the simulation of drained and undrained strain-controlled triaxial compression tests. The model is then used to back-analyze the measured response of normally consolidated to moderately overconsolidated specimens of a soft estuarine soil in undrained triaxial compression. The model captures aspects of soil behaviour that cannot be simulated using time-independent elastic–plastic models. Specifically, it can capture the dependence of stress–strain relationships and undrained shear strength on strain rate, the development of irrecoverable plastic strains at constant stress (creep), and the relaxation of stresses at constant strain.
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Seah, K. H. W., J. Hemanth i S. C. Sharma. "Effect of high-rate heat transfer during casting on the strength, hardness and wear behaviour of aluminium—quartz particulate metal matrix composites". Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture 217, nr 5 (1.05.2003): 651–59. http://dx.doi.org/10.1243/095440503322011371.
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This paper describes research on aluminium-based metal matrix composites (MMCs) reinforced with quartz particles cast in sand moulds using high-rate heat transfer techniques during solidification by means of metallic and non-metallic chills. The MMCs were fabricated by dispersing 3, 6 and 9 wt% of quartz particles ranging from 30 to 100μm in size in molten aluminium alloy above the liquidus temperature. The resulting composites, cast using chills, were tested for their strength, hardness and wear resistance. These properties of the MMCs were found to improve with the rate of heat transfer during casting. This rate of heat transfer is in turn dependent on the chill size and the chill material. After wear testing, the material surfaces were examined using scanning electron microscopy (SEM), and the wear mechanisms were analysed.
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Mazur, Karolina, i Stanisław Kuciel. "Mechanical and Hydrothermal Aging Behaviour of Polyhydroxybutyrate-Co-Valerate (PHBV) Composites Reinforced by Natural Fibres". Molecules 24, nr 19 (30.09.2019): 3538. http://dx.doi.org/10.3390/molecules24193538.
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Biodegradable composites based on poly (3-hydroxybutyrate-co-3-hydroxyvalerate), reinforced with 7.5% or 15% by weight of wood fibers (WF) or basalt fibers (BF) were fabricated by injection molding. BF reinforced composites showed improvement in all properties, whereas WF composites showed an increase in Young’s modulus values, but a drop in strength and impact properties. When compared with the unmodified polymer, composites with 15% by weight of BF showed an increase of 74% in Young’s modulus and 41% in impact strength. Furthermore, the experimentally measured values of Young’s modulus were compared with values obtained in various theoretical micromechanical models. The Haplin-Kardas model was found to be in near approximation to the experimental data. The morphological aspect of the biocomposites was studied using scanning electron microscopy to obtain the distribution and interfacial adhesion of the fibers. Additionally, biodegradation tests of the biocomposites were performed in saline solution at 40 °C by studying the weight loss and mechanical properties. It was observed that the presence of fibers affects the rate of water absorption and the highest rate was seen for composites with 15% by weight of WF. This is dependent on the nature of the fiber. After both the first and second weeks mechanical properties decreased slightly about 10%.
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Subadra, Sharath P., i Paulius Griskevicius. "Effect of Hybridization and Ply Waviness on the Flexural Strength of Polymer Composites: An Experimental and Numerical Study". Polymers 14, nr 7 (27.03.2022): 1360. http://dx.doi.org/10.3390/polym14071360.
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The study aims to ascertain the influence of hybridisation and ply waviness on the flexural behaviour of polymer composites. Two different resin systems, namely epoxy and Poly(methyl methacrylate)-PMMA, were chosen for the study, wherein two batches of carbon/glass hybrid composites (CGHC) were fabricated with the two resin systems. In addition to CGHC samples, four other neat batches with waviness (glass/epoxy and glass/PMMA) were prepared to study the effect of out-of-plane ply waviness. Two sets were additionally made with in-plane waviness (angles ranging from 15–35°) with epoxy to further understand the effect of waviness on flexural behaviour. Thereafter, two more batches of samples with neither waviness nor hybrid architectures were tested to achieve a better understanding of hybridization and the presence of waviness. It was seen that the hybridization of polymer composites introduces a pseudo-ductile behaviour in brittle composites, which makes the failure more predictable. An energy-based model was implemented to quantify the ductility introduced by hybridization. The presence of in-plane waviness increased the flexural load but reduced the modulus considerably. The presence of out-of-plane waviness decreased the flexural properties of composites drastically, though the displacement rate was seen to increase considerably. From the comparison between epoxy and PMMA, it was seen that PMMA exhibited similar flexural properties vis-à-vis epoxy. PMMA is easy to re-cycle and thus could serve as an ideal replacement for epoxy resin. Finally, a numerical model was built based on an LS-DYNA commercial solver; the model predicted the flexural behaviour close to what was seen in the experiments. The model could be calibrated correctly by ascertaining the influence of failure strain in the longitudinal direction, which is fibre dependent, and the failure strain in the transverse direction, which is matrix dependent.
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Kim, Eun-jin, i Rainer Hollerbach. "Exact Time-Dependent Solutions and Information Geometry of a Rocking Ratchet". Symmetry 14, nr 2 (3.02.2022): 314. http://dx.doi.org/10.3390/sym14020314.
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The noise-induced transport due to spatial symmetry-breaking is a key mechanism for the generation of a uni-directional motion by a Brownian motor. By utilising an asymmetric sawtooth periodic potential and three different types of periodic forcing G(t) (sinusoidal, square and sawtooth waves) with period T and amplitude A, we investigate the performance (energetics, mean current, Stokes efficiency) of a rocking ratchet in light of thermodynamic quantities (entropy production) and the path-dependent information geometric measures. For each G(t), we calculate exact time-dependent probability density functions under different conditions by varying T, A and the strength of the stochastic noise D in an unprecedentedly wide range. Overall similar behaviours are found for different cases of G(t). In particular, in all cases, the current, Stokes efficiency and the information rate normalised by A and D exhibit one or multiple local maxima and minima as A increases. However, the dependence of the current and Stokes efficiency on A can be quite different, while the behaviour of the information rate normalised by A and D tends to resemble that of the Stokes efficiency. In comparison, the irreversibility measured by a normalised entropy production is independent of A. The results indicate the utility of the information geometry as a proxy of a motor efficiency.
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Takata, Ken, Kohsaku Ushioda i Masao Kikuchi. "Precipitation Behaviour of Mg and Si at RT in Pre-Aged Al-Mg-Si Alloys". Materials Science Forum 519-521 (lipiec 2006): 233–38. http://dx.doi.org/10.4028/www.scientific.net/msf.519-521.233.
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The precipitation behavior of Mg and Si during storage at RT in Al-Mg-Si alloys pre-aged at 90°C was studied using a tensile test and differential scanning calorimetry (DSC) measurement. Specimens were solutionized at 530°C, water-quenched and then pre-aged for 2, 6 and 12 hours at 90°C during which small precipitates were formed. In the pre-aged alloy, the strengthening rate at RT has two stages. In the initial stage, the yield strength increases slowly with the aging time and in the final stage, it increases rapidly. In the initial stage, the strength in the pre-aged alloy is smaller than that in the non pre-aged alloy, while in the final stage, the strength in the pre-aged alloy is larger than that in the non pre-aged alloy. Furthermore, the period of the initial stage is dependent on the pre-aging period at 90°C. The DSC curves of alloys in the initial stage do not show the presence of clusters, while those in the final stage do. It seems that in the initial stage Mg and Si atoms accumulate around the small precipitates that have been formed in pre-aging at 90°C while in the final stage, the clusters of these atoms are formed.
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Li, Chun, Jian Ouyang, Fangjie Dou i Jingtao Shi. "Mechanism Influencing the Drying Behavior of Bitumen Emulsion". Materials 14, nr 14 (12.07.2021): 3878. http://dx.doi.org/10.3390/ma14143878.
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The drying process of bitumen emulsion largely dominates the strength development of emulsion-based mixtures for pavement structure, thus it can be used to judge the quality of bitumen emulsion. However, the drying behaviour of bitumen emulsions was seldom considered. The emulsion drying and film formation theory are employed to study the drying process of different bitumen emulsions with a thin layer. Results indicated the drying process of bitumen emulsion can be divided into three stages: (a) an initial high evaporation rate stage; (b) an intermediate stage with a rapidly decreasing evaporation rate; (c) a final stage with a very small evaporation rate. The boundaries among the three stages can be identified by studying the water evaporation rate. Three drying parameters, i.e., the critical volume fractions of bitumen defining the boundaries among the three stages and the maximum packing fraction of bitumen droplets, are proposed to quantitatively characterize the drying behavior of bitumen emulsion. High values of these parameters indicate a bitumen emulsion that has rapid drying behavior. Therefore, these parameters are independent of the emulsifier type, but they are highly dependent on the bitumen’s droplet size. These drying parameters increase with a decrease in bitumen droplet size. Therefore, bitumen emulsion with a smaller size distribution of bitumen droplets can have a more rapid drying behavior, which is recommended in real engineering.
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Chen, Xingzhou, Hai Jiang, Lili Chen, Wei Du i Sheng Gong. "Experimental Study on Creep Characteristics of Unloaded Rock Masses for Excavation of Rock Slopes in Cold Areas". Applied Sciences 13, nr 5 (28.02.2023): 3138. http://dx.doi.org/10.3390/app13053138.
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Seasonal freeze–thaw environments are one of the key factors that aggravate the mechanical strength decay of excavated and unloaded rock masses on reservoir banks in cold areas. To study the time-dependent mechanical properties of an excavated and unloaded rock mass on a bank slope under freeze–thaw action, triaxial unloading tests were carried out on sandstone, freeze–thaw tests simulating freezing strength were conducted, and triaxial creep tests were implemented with graded incremental loading on unloaded specimens subjected to freeze–thaw action. The test results showed that the total deformation of the unloaded specimens is significantly increased compared with the conventional specimens, and the lateral direction is more likely to produce creep behaviour than the axial direction. The level of confining pressure determines the level of creep deformation of unloaded specimens and affects the variation law of creep rate. The creep behaviour of the unloaded specimens is aggravated by freeze–thaw action and, the longer the freezing period, the larger the creep strain share, and the creep rate increases significantly. The creep damage pattern of the unloaded specimens subjected to freeze–thaw action is mainly manifested as shear damage, and the creep process intensifies the derivation of tension-type cracks in the specimens. The higher the confining pressure of the unloaded specimen, the more obvious the plastic characteristics and the weaker the brittle characteristics during creep failure. The freeze–thaw action significantly reduces the long-term strength of the unloaded specimen, which is approximately 50~55% of the instantaneous strength. The long-term strength decays significantly with an increasing freezing period, and the research results can provide a theoretical reference for the evaluation of the long-term stability of excavated and unloaded rock masses in cold areas.
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Coats, Rebecca, Jackie E. Kendrick, Paul A. Wallace, Takahiro Miwa, Adrian J. Hornby, James D. Ashworth, Takeshi Matsushima i Yan Lavallée. "Failure criteria for porous dome rocks and lavas: a study of Mt. Unzen, Japan". Solid Earth 9, nr 6 (8.11.2018): 1299–328. http://dx.doi.org/10.5194/se-9-1299-2018.
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Abstract. The strength and macroscopic deformation mode (brittle vs. ductile) of rocks is generally related to the porosity and pressure conditions, with occasional considerations of strain rate. At high temperature, molten rocks abide by Maxwell's viscoelasticity and their deformation mode is generally defined by strain rate or reciprocally by comparing the relaxation timescale of the material (for a given condition) to the observation timescale – a dimensionless ratio known as the Deborah (De) number. Volcanic materials are extremely heterogeneous, with variable concentrations of crystals, glass–melt, and vesicles (of different sizes), and a complete description of the conditions leading to flow or rupture as a function of temperature, stress and strain rate (or timescale of observation) eludes us. Here, we examined the conditions which lead to the macroscopic failure of variably vesicular (0.09–0.35), crystal-rich (∼ 75 vol %), pristine and altered dome rocks (at ambient temperature) and lavas (at 900 °C) from Mt. Unzen volcano, Japan. We found that the strength of the dome rocks decreases with porosity and is commonly independent of strain rate; when comparing pristine and altered rocks, we found that the precipitation of secondary mineral phases in the original pore space caused minor strengthening. The strength of the lavas (at 900 °C) also decreases with porosity. Importantly, the results demonstrate that these dome rocks are weaker at ambient temperatures than when heated and deformed at 900 °C (for a given strain rate resulting in brittle behaviour). Thermal stressing (by heating and cooling a rock up to 900 °C at a rate of 4 °C min−1, before testing its strength at ambient temperature) was found not to affect the strength of rocks.In the magmatic state (900 °C), the rheology of the dome lavas is strongly strain rate dependent. Under conditions of low experimental strain rate (≤ 10−4 s−1), ductile deformation dominated (i.e. the material sustained substantial, pervasive deformation) and displayed a non-Newtonian shear thinning behaviour. In this regime, the apparent viscosities of the dome lavas were found to be essentially equivalent, independent of vesicularity, likely due to the lack of pore pressurisation and efficient pore collapse during shear. At high experimental strain rates ( ≥ 10−4 s−1) the lavas displayed an increasingly brittle response (i.e. deformation resulted in failure along localised faults); we observed an increase in strength and a decrease in strain to failure as a function of strain rate. To constrain the conditions leading to failure of the lavas, we analysed and compared the critical Deborah number at failure (Dec) of these lavas to that of pure melt (Demelt = 10−3–10−2; Webb and Dingwell, 1990). We found that the presence of crystals decreases Dec to between 6.6×10−4 and 1×10−4. The vesicularity (φ), which dictates the strength of lavas, further controls Dec following a linear trend. We discuss the implications of these findings for the case of magma ascent and lava dome structural stability.
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TIKOO, Kulbhushan, Q. Anwar HAMID i Ziledar ALI. "Structure of active chromatin: higher-order folding of transcriptionally active chromatin in control and hypothyroid rat liver". Biochemical Journal 322, nr 1 (15.02.1997): 289–96. http://dx.doi.org/10.1042/bj3220289.
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Investigations have been carried out into the salt-induced higher-order folding in the transcriptionally active chromatin region of rat liver nuclei by nuclease digestion, sedimentation and CD. The sensitivity of active chromatin in nuclei to micrococcal nuclease was suppressed by raising the ionic strength from 25 to 90 mM, indicating the occurrence of salt-induced condensation. The rate of sedimentation of fractionated inactive chromatin fragments of both moderate (∼3.5 kbp) and large (∼8.8 kbp) size increased maximally to the same extent, while that of active chromatin fragments was dependent on their size. The rate of sedimentation of moderately sized active chromatin fragments (∼5.5 kbp) showed a maximal 15% increase at 90 mM ionic strength. In contrast, a large increase (at least 60%) in the sedimentation rate of large active chromatin fragments (∼21 kbp) was observed at 65 mM ionic strength. A reasonable degree of higher-order folding was observed in large active chromatin fragments even at 25 mM ionic strength. On considering the percentage increase in sedimentation rate as a measure of the higher-order folding of chromatin, a different type of higher-order folding was observed in active chromatin fragments. Although the percentage increase in sedimentation decreased from 40 to 24% with an increase in the size of active chromatin from ∼3 to ∼9 kbp, a further increase in size up to 16 kbp brought the percentage increase back to 40%. CD studies agreed with the conclusions drawn from sedimentation studies. Active chromatin from hypothyroid rats showed similar folding behaviour, but the order of folding was slightly lower than for control active chromatin, at all sizes.
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Lu, Jiahai, Ping Zhu, Qinghui Ji i Zhang Cheng. "Experimental Study of In-plane Mechanical Properties of Carbon Fibre Woven Composite at Different Strain Rates". Polymers and Polymer Composites 25, nr 4 (maj 2017): 289–98. http://dx.doi.org/10.1177/096739111702500406.
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Carbon fibre woven composite has been increasingly employed in engineering applications undergoing complex loading conditions. For effective use of composite material in dynamic applications, it is essential to fully understand the mechanical behaviour of composite at different strain rates. In the present study, both in-plane tensile and compressive experiments loaded at 0 degree axial direction and 45 degree off-axial direction of a TC33 carbon fibre woven composite were investigated over the strain rate range from 0.001 to 1000 s−1. High strain rate tests were carried out using Split Hopkinson Pressure and Tensile Bar apparatus respectively. The results indicated that the in-plane mechanical properties and failure patterns were strain rate sensitive under both tensile and compressive loadings. The mechanical properties, failure patterns and strain rate effect also showed highly direction dependent and tension/compression asymmetric characteristic within the considered strain rate range. For higher strain rate sensitivity under compression than that under tension, the asymmetry of mechanical properties was less obvious with the increase of strain rate. Finally, two phenomenal models were proposed to quantitatively fit the relationship between strength property and strain rate.
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Colombo, Isabella, Matteo Colombo, Anna Magri, Giulio Zani i Marco di Prisco. "Textile Reinforced Mortar at High Temperatures". Applied Mechanics and Materials 82 (lipiec 2011): 202–7. http://dx.doi.org/10.4028/www.scientific.net/amm.82.202.
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Textile Reinforced Mortar (TRM) is a composite made by fine grained matrix and glass fabric reinforcement. The main advantages of this material are the reinforcement orientation in the tensile stress direction, no concrete cover requirement against corrosion and the capability to produce thin and light weight elements. Special attention was given by researchers to the time dependent loss in strength of AR-glass reinforcement embedded in a cement based matrix. Some research has shown durability models to calculate the amount to the strength loss related to material, humidity and temperature. Nevertheless, the behaviour of TRM when exposed to high temperature requires further investigations. A suitable experimental programme was planned to investigate the behaviour of TRM when exposed to high temperatures. Uniaxial tensile tests were performed after thermal cycle on 400 mm x 70 mm specimens 6 mm thick, reinforced with 2 layer of AR-glass fabric. Several thermal thresholds (20, 200, 400 and 600°C) were considered for the mechanical characterization in fire condition. Thermal cycles were performed in an oven using a heating rate of 30°C/h up to the maximum temperature and by a cooling branch at 15°C/h after a stabilization phase at the maximum temperature.
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Verberne, Berend A., Martijn P. A. van den Ende, Jianye Chen, André R. Niemeijer i Christopher J. Spiers. "The physics of fault friction: insights from experiments on simulated gouges at low shearing velocities". Solid Earth 11, nr 6 (13.11.2020): 2075–95. http://dx.doi.org/10.5194/se-11-2075-2020.
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Abstract. The strength properties of fault rocks at shearing rates spanning the transition from crystal–plastic flow to frictional slip play a central role in determining the distribution of crustal stress, strain, and seismicity in tectonically active regions. We review experimental and microphysical modelling work, which is aimed at elucidating the processes that control the transition from pervasive ductile flow of fault rock to rate-and-state-dependent frictional (RSF) slip and to runaway rupture, carried out at Utrecht University in the past 2 decades or so. We address shear experiments on simulated gouges composed of calcite, halite–phyllosilicate mixtures, and phyllosilicate–quartz mixtures performed under laboratory conditions spanning the brittle–ductile transition. With increasing shear rate (or decreasing temperature), the results consistently show transitions from (1) stable velocity-strengthening (v-strengthening) behaviour, to potentially unstable v-weakening behaviour, and (2) back to v strengthening. Sample microstructures show that the first transition seen at low shear rates and/or high temperatures represents a switch from pervasive, fully ductile deformation to frictional sliding involving dilatant granular flow in localized shear bands where intergranular slip is incompletely accommodated by creep of individual mineral grains. A recent microphysical model, which treats fault rock deformation as controlled by competition between rate-sensitive (diffusional or crystal–plastic) deformation of individual grains and rate-insensitive sliding interactions between grains (granular flow), predicts both transitions well. Unlike classical RSF approaches, this model quantitatively reproduces a wide range of (transient) frictional behaviours using input parameters with direct physical meaning, with the latest progress focusing on incorporation of dynamic weakening processes characterizing co-seismic fault rupture. When implemented in numerical codes for crustal fault slip, the model offers a single unified framework for understanding slip patch nucleation and growth to critical (seismogenic) dimensions, as well as for simulating the entire seismic cycle.
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Kozłowski, Marcin, Kinga Zemła, Magda Kosmal i Ołeksij Kopyłow. "Experimental and FE Study on Impact Strength of Toughened Glass–Retrospective Approach". Materials 14, nr 24 (12.12.2021): 7658. http://dx.doi.org/10.3390/ma14247658.
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Due to the high cost of experiments commonly performed to verify the resistance of glass elements to impact loads, numerical models are used as an alternative to physical testing. In these, accurate material parameters are crucial for a realistic prediction of the behaviour of glass panels subjected to impact loads. This applies in particular to the glass’s strength, which is strictly dependent on the strain rate. The article reports the results of an extensive experimental campaign, in which 185 simply supported toughened glass samples were subjected to hard-body impacts. The study covers a wide range of glass thicknesses (from 5 to 15 mm), and it aims to determine a critical drop height causing fracture of the glass. Moreover, a 3D numerical model of the experimental set-up was developed to reproduce the experiments numerically and retrospectively to determine the peak stress in glass that developed during the impact. Based on the results of numerical simulations, a load duration factor of 1.40 for toughened glass for impact loads is proposed. In addition, the paper includes a case study to demonstrate the use of the modelling methodology and results of the work on a practical example of an internal glass partition wall.
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Elsenheimer, Hendrik C., Jan Tabellion, Florian Paul i Jürgen Haußelt. "Distribution of the Local Electric Field during Electrophoretic Deposition of an Alumina Suspension on a Membrane". Key Engineering Materials 412 (czerwiec 2009): 15–20. http://dx.doi.org/10.4028/www.scientific.net/kem.412.15.
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The spatially distributed local electric field strength during the electrophoretic deposition (EPD) of alumina suspensions on a membrane is within the scope of the present article. The water-based alumina suspensions were optimized in order to achieve stable suspensions, high deposition rates and maximum green densities of the deposited bodies. In-situ measurements of the local potential drop inside the EPD-cell were carried out using a computer assisted process control set-up with electronic data acquisition. The behaviour of the spatial- and time-dependent electric field distribution was calculated from measured potential drops. The influence of varrying input voltages on the output parameters, such as deposition rate and green density for EPD on membranes was investigated and is discussed. It is shown that the distribution of the local electric field depends on the applied voltage and on time for the case of higher voltages. A dependance of the local electrical fields on the deposition rate is suggested as well.
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Esteban, Beatriz, i Norbert Gebbeken. "A detailed comparison of two material models for concrete in the dynamic loading regime, RHT and HPG". International Journal of Protective Structures 8, nr 2 (czerwiec 2017): 260–86. http://dx.doi.org/10.1177/2041419617707104.
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Throughout the last decades, great attention has been given to model the dynamic behaviour of concrete. As such, numerous material models have been conceived in hydrocodes to describe the complex behaviour of this composite material subjected to large deformations leading to damage and failure. Concrete shows, for instance, strain rate dependency as well as hydrostatic pressure dependency. This article focuses on the comparison of two material models conceived for such purpose. These are the RHT model (RHT - Riedel, Hiermaier, Thoma) developed at the Fraunhofer Ernst-Mach-Institut and the HPG (HPG - Hartmann, Pietzsch, Gebbeken) model developed at the University of the Bundeswehr Munich, both of which have been proven to be successful in a variety of scenarios. They are macro-level models, i.e., they regard concrete as a homogeneous material. Both models incorporate the traditional splitting in hydrocodes of the hydrostatic and the deviatoric response. On the one hand, both material models have three pressure-dependent limit surfaces in the stress space to characterise concrete strength. These are the elastic limit surface, the failure surface and the residual strength surface, the latter being related to a damage model. Strain rate effects are inherent in the models. On the other hand, both material models use the p–α formulation in the Mie–Grüneisen equation of state. The parameters of this equation are, however, differently calculated. A final comparison of these two models is done by conducting numerical simulations where the RHT and the HPG models are used as material models. The scenario is a contact detonation as an example of a high strain rate problem. Such an in-depth and detailed comparison has not been done to date. It aims to help the user decide which material model to choose as well as to provide ideas for future development in the field of material modelling.
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Fisher, Tom, José Humberto S. Almeida Jr, Brian G. Falzon i Zafer Kazancı. "Tension and Compression Properties of 3D-Printed Composites: Print Orientation and Strain Rate Effects". Polymers 15, nr 7 (29.03.2023): 1708. http://dx.doi.org/10.3390/polym15071708.
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This study examines the impact of three factors on the tensile and compressive behaviour of 3D-printed parts: (1) the addition of short carbon fibres to the nylon filament used for 3D printing, (2) the infill pattern, and (3) the speed at which the materials are strained during testing. The results show that adding carbon fibres to the nylon filament reduces variability between tests and emphasises the effect of print orientation. When the infill pattern is aligned with the direction of loading, the tensile strength of all samples increases, with the largest increase of 100% observed in the carbon fibre-reinforced samples, compared to a 37% increase in the strength of nylon samples. The carbon fibre-reinforced samples are also highly dependent on strain rate, with a 60% increase in tensile strength observed at a faster testing speed of 300 mm/min (9 min−1) compared to 5 mm/min (15 min−1). Nylon samples show a decrease of approximately 10% in tensile strength at the same increased speed. The compressive strength of the composite samples increases by up to 130% when the print path is parallel to the loading direction. Increases of up to 50% are observed in the compressive modulus of the composite samples at a test speed of 255 mm/min (9 min−1) compared to 1.3 mm/min (0.05 min−1). Similar trends are not seen in pure nylon samples. This study is the first to report on the variation of Poisson’s ratio of short carbon fibre-reinforced 3D-printed parts. The results show increases of up to 34% and 76% in the tensile and compressive Poisson’s ratios, respectively, when printing parameters are altered. The findings from this research will contribute to the design and numerical modelling of 3D-printed composites.
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Tober, Gerhard, Okechukwu Anopuo i Petra Maier. "Lead as Test Rolling Material for Hot Complex Rolling of Steel". Advanced Materials Research 428 (styczeń 2012): 84–88. http://dx.doi.org/10.4028/www.scientific.net/amr.428.84.
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The low deforming force of Lead (Pb) and the proximity of its stress-strain response make it readily preferred as test material for laboratory modelling of complex hot steel rolling. Structural steel recrystallises from a temperature of approximately 500 °C. For Pb, this process starts within the range of-3 °C to 0 °C. The room temperature rolling of Pb delivers reasonable information of hot rolling of steel. This is however dependent on various parameters which include; deformation rate, degree of deformation, alloying elements and previous heat treatments. This work studies the deformation behaviour of Pb 99.94 Cu by carrying out rolling operations at different deformation rates and deformation degrees. Tension and compression tests were used to determine the ultimate tensile and compression strength, the yield strength and the Young´s Modulus, respectively. Flow curves were subsequently determined and compared to that of selected structural steels. The microstructures were analysed and were correlated with the deformation parameters taking cognisance of the role of recrystallisation during the rolling process.
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Arola, D., S. Ghods, C. Son, S. Murcia i E. A. Ossa. "Interfibril hydrogen bonding improves the strain-rate response of natural armour". Journal of The Royal Society Interface 16, nr 150 (styczeń 2019): 20180775. http://dx.doi.org/10.1098/rsif.2018.0775.
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Fish scales are laminated composites that consist of plies of unidirectional collagen fibrils with twisted-plywood stacking arrangement. Owing to their composition, the toughness of scales is dependent on the intermolecular bonding within and between the collagen fibrils. Adjusting the extent of this bonding with an appropriate stimulus has implications for the design of next-generation bioinspired flexible armours. In this investigation, scales were exposed to environments of water or a polar solvent (i.e. ethanol) to influence the extent of intermolecular bonding, and their mechanical behaviour was evaluated in uniaxial tension and transverse puncture. Results showed that the resistance to failure of the scales increased with loading rate in both tension and puncture and that the polar solvent treatment increased both the strength and toughness through interpeptide bonding; the largest increase occurred in the puncture resistance of scales from the tail region (a factor of nearly 7×). The increase in strength and damage tolerance with stronger intermolecular bonding is uncommon for structural materials and is a unique characteristic of the low mineral content. Scales from regions of the body with higher mineral content underwent less strengthening, which is most likely the result of interference posed by the mineral crystals to intermolecular bonding. Overall, the results showed that flexible bioinspired composite materials for puncture resistance should enrol constituents and complementary processing that capitalize on interfibril bonds.
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Zhou, Tao, Jianbo Zhu i Heping Xie. "Mechanical and Volumetric Fracturing Behaviour of Three-Dimensional Printing Rock-like Samples Under Dynamic Loading". Rock Mechanics and Rock Engineering 53, nr 6 (14.03.2020): 2855–64. http://dx.doi.org/10.1007/s00603-020-02084-5.
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AbstractHeterogeneous rock contains numerous pre-existing three-dimensional (3D) cracks, which control its mechanical and fracturing properties. Considerable effort has been devoted to studying the volumetric fracturing behaviour of rock under static loading conditions. Although rock masses are often subject to dynamic impacts such as earthquakes and blasting, the mechanical and volumetric fracturing behaviour of rock under dynamic loading is still poorly understood. In this paper, dynamic laboratory tests were performed on 3D-printed artificial rock samples with 3D embedded flaws created during three-dimensional printing (3DP), with the aim of studying the volumetric fracturing and mechanical properties of these samples under impact with high strain rate. The results show that the dynamic compressive strength and the tangent modulus decrease with an increasing number of flaws, but have very limited effects on the ratio of the fracture initiation stress of the first crack to the peak stress of the sample, the maximum axial strain of the sample and the volumetric fracturing behaviour of the sample. The tensile failure of a sample is caused by the continuous extension of wing cracks from the outer flaw tips. The mechanical and volumetric fracturing behaviour of samples with 3D embedded flaws are strain rate dependent. The tangential modulus and the ratio of the fracture initiation stress of the crack to the peak stress increase significantly when the loading type changes from static compression to dynamic compression. Under dynamic compression, wing cracks can continuously extend to the sample ends, whereas under static compression, wing cracks can intermittently extend only a limited distance. Moreover, the fracturing behaviour of 3D flaw differs from that of 2D flaws under dynamic loading. Under high strain rate loading, wing cracks generated at 3D flaw tips lead to splitting failure of the sample, while shear cracks formed at 2D flaw tips result predominant shear failure of the sample. The findings in this paper could facilitate a better understanding of rock failure subjected to dynamic loading conditions.
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Pineau, André. "Crossing grain boundaries in metals by slip bands, cleavage and fatigue cracks". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 373, nr 2038 (28.03.2015): 20140131. http://dx.doi.org/10.1098/rsta.2014.0131.
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The size and the character (low and large angle, special boundaries, tilt and twist boundaries, twins) of the grain boundaries (GBs) in polycrystalline materials influence their strength and their fracture toughness. Recent studies devoted to nanocrystalline (NC) materials have shown a deviation from the Hall–Petch law. Special GBs formed by Σ3 twins in face-centred cubic metals are also known to have a strong effect on the mechanical behaviour of these metals, in particular their work-hardening rate. Grain orientation influences also crack path, the fracture toughness of body-centred cubic (BCC) metals and the fatigue crack growth rate of microstructurally short cracks. This paper deals both with slip transfer at GBs and with the interactions between propagating cracks with GBs. In the analysis of slip transfer, the emphasis is placed on twin boundaries (TBs) for which the dislocation reactions during slip transfer are analysed theoretically, experimentally and using the results of atomic molecular simulations published in the literature. It is shown that in a number of situations this transfer leads to a normal motion of the TB owing to the displacement of partial dislocations along the TB. This motion can generate a de-twinning effect observed in particular in NC metals. Crack propagation across GBs is also considered. It is shown that cleavage crack path behaviour in BCC metals is largely dependent on the twist component of the GBs. A mechanism for the propagation of these twisted cracks involving a segmentation of the crack front and the existence of intergranular parts is discussed and verified for a pressure vessel steel. A similar segmentation seems to occur for short fatigue cracks although, quite surprisingly, this crossing mechanism for fatigue cracks does not seem to have been examined in very much detail in the literature. Metallurgical methods used to improve the strength of the materials, via grain boundaries, are briefly discussed.
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Troncone, A., L. Pugliese, A. Parise i E. Conte. "A Simple Method to Reduce Mesh Dependency in Modelling Landslides Involving Brittle Soils". Géotechnique Letters 12, nr 3 (1.09.2022): 1–27. http://dx.doi.org/10.1680/jgele.22.00023.
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This paper focuses on the numerical simulation of the deformation processes occurring in the slopes when soils with strain-softening behaviour are involved. In these circumstances, a progressive failure may occur with the consequent motion of the unstable soil mass in the post-failure stage. This problem can be only solved using advanced numerical techniques capable also of accounting for the occurrence of large deformations. However, the solution is generally mesh dependent and may be affected by lack of convergence. In the present study, the material point method (MPM) is employed to simulate the occurrence of large deformations, in conjunction with a strain-softening Mohr-Coulomb constitutive model, in which the shear strength parameters are reduced as a function of the accumulated deviatoric plastic strain, and a model parameter controlling the rate of strength decrease. To evaluate this parameter and to reduce the effects of the mesh dependency on the numerical solution, a novel procedure based on the results of direct shear tests is presented. This methodology is completely analytical and requires few parameters with a clear physical meaning and of simple experimental determination. Some simulations are performed to assess the reliability of the proposed procedure.
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Rist, M. A., i S. A. F. Murrell. "Ice triaxial deformation and fracture". Journal of Glaciology 40, nr 135 (1994): 305–18. http://dx.doi.org/10.1017/s0022143000007395.
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AbstractAn experimental investigation into the mechanical behaviour of polycrystalline ice in triaxial compression has been conducted using conditions generally favourable to brittle fracture and microcracking. Under triaxial stresses at high strain rate, ice failure occurs by abrupt shear fracturing, generally inclined at about 45° to the maximum principal stress. At −20°C, such failure is suppressed by the imposition of a small confining pressure, allowing a transition to ductile-type flow accompanied by distributed microcracking, but at —40°C shear fracture persists under confinement of up to at least 50 MPa. For low confining pressures (< 10 MPa), brittle strength is strongly pressure-dependent; above this it is pressure-independent. Evidence is presented that suggests this may reflect a change from a fracture process influenced by friction to fracture initiated by localized yielding. Ductile yield strength is found to be little influenced by confining pressure despite the inhibition of cracking that leads to greatly contrasting observed crack densities. Flow conforms to the well-known power law for ice withQ= 69 J mol−1andn= 4.2 over the temperature range −20° to −4-5° C Under these conditions, microcracking in ice appears to remain remarkably stable and non-interacting.
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Rist, M. A., i S. A. F. Murrell. "Ice triaxial deformation and fracture". Journal of Glaciology 40, nr 135 (1994): 305–18. http://dx.doi.org/10.3189/s0022143000007395.
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AbstractAn experimental investigation into the mechanical behaviour of polycrystalline ice in triaxial compression has been conducted using conditions generally favourable to brittle fracture and microcracking. Under triaxial stresses at high strain rate, ice failure occurs by abrupt shear fracturing, generally inclined at about 45° to the maximum principal stress. At −20°C, such failure is suppressed by the imposition of a small confining pressure, allowing a transition to ductile-type flow accompanied by distributed microcracking, but at —40°C shear fracture persists under confinement of up to at least 50 MPa. For low confining pressures (< 10 MPa), brittle strength is strongly pressure-dependent; above this it is pressure-independent. Evidence is presented that suggests this may reflect a change from a fracture process influenced by friction to fracture initiated by localized yielding. Ductile yield strength is found to be little influenced by confining pressure despite the inhibition of cracking that leads to greatly contrasting observed crack densities. Flow conforms to the well-known power law for ice withQ= 69 J mol−1andn= 4.2 over the temperature range −20° to −4-5° C Under these conditions, microcracking in ice appears to remain remarkably stable and non-interacting.
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Egan, J. M. "A viscoelastic analysis of the tensile weakening of deep femoral head articular cartilage". Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine 214, nr 3 (1.03.2000): 239–47. http://dx.doi.org/10.1243/0954411001535732.
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Articular cartilage from below the surface of the femoral head of the hip joint shows a profound age-dependent weakening in its tensile mechanical properties. This ageing is also associated with a reduced viscoelastic response in the older tissue. A constitutive model of the viscoelastic behaviour of deep articular cartilage (as discussed by Egan in 1988) is used to generate a graphical pattern which represents the mechanical behaviour. This constitutive approach suggests that the tensile weakening of the older cartilage is due to an age-related reduction in the recruitment of load-carrying structures as the tissue is deformed. The viscoelastic constitutive model also predicts a reduction in the tensile strength of deep articular cartilage with rate of deformation. This prediction is supported by experimental fracture stress data. A weakening of the tensile integrity of the microstructure of articular cartilage could make the tissue less able to sustain normal compressive physiological loading without damage and thus make the tissue more susceptible to osteoarthritic degeneration. The constitutive approach indicates that the weakening of the older tissue may be related to changes within the microstructure which determine how applied mechanical energy is stored and dissipated.