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Z Bartczak - One of the best experts on this subject based on the ideXlab platform.
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plastic deformation behavior of β phase isotactic polypropylene in plane Strain Compression at elevated temperatures part b polymer physics
Journal of Polymer Science, 2008Co-Authors: E Lezak, Z BartczakAbstract:Isotactic polypropylene (iPP) rich in β crystal modification was deformed by plane-Strain Compression at T = 55-100 °C. The evolution of phase structure, morphology, and orientation were studied by DSC, X-Ray, and SEM. The most important deformation mechanisms found were interlamellar slip operating in the amorphous layers, resulting in numerous fine deformation bands and the crystallographic slip systems, including the (110)[001]β chain slip and (110)[$1{\bar {1}}0$]β transverse slip. Shear within deformation bands leads to β[rightward arrow]α solid state phase transformation in contrast to β[rightward arrow]smectic transformation observed at room temperature. Newly formed α crystallites deform with an advancing Strain by crystallographic slip mechanism, primarily the (010)[001]α chain slip. As a result of deformation and phase transformation within deformation bands β lamellae are locally destroyed and fragmented into smaller crystals. Deformation to high Strains, above e = 1, brings further heavy fragmentation of lamellae, followed by fast rotation of crystallites with chain axis towards the direction of flow FD. This process, together with still active crystallographic slip, leads to the final texture with molecular axis of both crystalline β and α phase oriented along FD. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 92-108, 2008
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plastic deformation behavior of β phase isotactic polypropylene in plane Strain Compression at elevated temperatures
Journal of Polymer Science Part B, 2008Co-Authors: E Lezak, Z BartczakAbstract:Isotactic polypropylene (iPP) rich in β crystal modification was deformed by plane-Strain Compression at T = 55-100 °C. The evolution of phase structure, morphology, and orientation were studied by DSC, X-Ray, and SEM. The most important deformation mechanisms found were interlamellar slip operating in the amorphous layers, resulting in numerous fine deformation bands and the crystallographic slip systems, including the (110)[001] β chain slip and (110)[110] β transverse slip. Shear within deformation bands leads to β→α solid state phase transformation in contrast to β→smectic transformation observed at room temperature. Newly formed α crystallites deform with an advancing Strain by crystallographic slip mechanism, primarily the (010)[001] α chain slip. As a result of deformation and phase transformation within deformation bands β lamellae are locally destroyed and fragmented into smaller crystals. Deformation to high Strains, above e = 1, brings further heavy fragmentation of lamellae, followed by fast rotation of crystallites with chain axis towards the direction of flow FD. This process, together with still active crystallographic slip, leads to the final texture with molecular axis of both crystalline β and a phase oriented along FD.
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high Strain deformation of polyethylenes in plane Strain Compression at elevated temperatures
Journal of Applied Polymer Science, 2007Co-Authors: E Lezak, Z BartczakAbstract:The deformation and recovery behavior of several polyethylenes and ethylene-based copolymers with various molecular architectures and a broad range of molecular masses and molecular mass distributions was studied. Because of the differences in the molecular characteristic, this series exhibited a relatively broad range of crystallite sizes and crystallinity levels. The samples were subjected to high Strain Compression under plane-Strain conditions at the elevated temperature of 80°C. The unloading of the compressed samples led to substantial nonelastic recovery of the Strain. The stress–Strain and recovery behavior was related to the molecular parameters. The results confirmed the common deformation scheme with four crossover points related to the activation of subsequent deformation mechanisms, as proposed by Strobl. Although the critical Strains, related to the activation of deformation of the crystalline component, are invariant, the critical Strain of the last point, which is related to the activation of chain disentanglement in the amorphous component, depends on the temperature of deformation. That critical Strain decreases from 1.0 to approximately 0.8–0.9 as the temperature of deformation increases from room temperature to 80°C. This shift results from an increase in the chain mobility with increasing temperature, and this makes modification of the molecular network through chain disentanglements easier. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 105: 14–24, 2007
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plastic deformation of the γ phase isotactic polypropylene in plane Strain Compression at elevated temperatures
Macromolecules, 2007Co-Authors: E Lezak, Z BartczakAbstract:Plastic deformation behavior of iPP homopolymer crystallized exclusively in the γ modification was studied. Samples of γ-iPP were obtained by isothermal crystallization under pressure of 200 MPa. Deformation experiments in plane−Strain Compression were performed in the temperature range of 55−100 °C. Samples of γ-iPP demonstrated higher modulus, higher yield stress, and flow stress, yet slightly lower ultimate Strain comparing to α-iPP in the entire range of temperature studied. During plastic deformation numerous fine shear bands, initiated by the interlamellar shear of the amorphous layers, start to develop already at the yield point. Their propagation across the sample causes a limited destruction of γ lamellae oriented perpendicularly to the direction of the band. Destroyed fragments of crystallites partially reconstruct into either mesophase (smectic) domains or crystals of α phase, depending on the deformation temperature. Mesophase is produced upon deformation at room temperature, while at 55 °C an...
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plastic deformation behavior of β phase isotactic polypropylene in plane Strain Compression at room temperature
Polymer, 2006Co-Authors: E Lezak, Z Bartczak, Andrzej GaleskiAbstract:Abstract Isotactic polypropylene (iPP) rich in β crystal modification (constituting 92% of crystalline phase) was deformed by the plane-Strain Compression with constant true Strain rate, at room temperature. The evolution of phase structure, morphology and orientation was studied by DSC, X-ray and SEM. The deformation sequence and the active deformation mechanisms were found out. The most important mechanisms were interlamellar slip operating in the amorphous layers, resulting in numerous fine deformation bands due to localization of deformation and the crystallographic slip systems, including the (110)[001] chain slip and (110)[1 1 ¯ 0] transverse slip. Shear within deformation bands leads to β → smectic and β → α solid state phase transformations. At room temperature the β → smectic transformation appeared to be the primary transformation, yielding the oriented smectic phase with high concentration of 19 wt.% at the true Strain of e = 1.49. The β → α yields only about 4 wt.% of new α-phase at the same Strain. As a result of the deformation and phase transformation within numerous fine deformation bands β-lamellae are locally destroyed and fragmented into smaller crystals. Another deformation mechanism is the cooperative kinking of lamellae, leading to their reorientation and formation of a chevron-like lamellar arrangement. At high Strains, above e = 1, an advanced crystallographic slip and high stretch of amorphous material due to interlamellar shear bring further heavy fragmentation of lamellar crystals, earlier fragmented partially by deformation bands. This fragmentation is followed by fast rotation of small unconStrained crystallites with chain axis towards the direction of flow, FD. This process leads to development of the final texture of the highly deformed β-iPP with molecular axis of both crystalline and smectic phases oriented along FD.
C M Sellars - One of the best experts on this subject based on the ideXlab platform.
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identification of rheological parameters on the basis of plane Strain Compression tests on specimens of various initial dimensions
Computational Materials Science, 2006Co-Authors: B Kowalski, C M Sellars, Maciej PietrzykAbstract:Abstract The work is based on the assumption that the flow stress of a material should be insensitive to the method of plastometric testing or to the size of the samples. It is generally observed, however, that various methods of testing yield different values of the flow stress. Endeavours are made to eliminate these differences and various methods of correction of the results of the tests have been developed. The particular objective of the present work is to check the capabilities of the inverse technique to obtain consistent flow stress data when this technique is applied to plane Strain Compression tests performed on one material with various dimensions of the specimens. The experiments included plane Strain Compression for specimens measuring 2.5, 5 and 10 mm initial thickness. The inverse algorithm developed by the authors was used in the investigation. Application of the inverse analysis to the interpretation of the results of these tests allowed the conclusion that the results obtained for various specimen geometries coincide very closely. This analysis has been further used for evaluation of various conventional methods for correction to account for the influence of inhomogeneity of Strain and temperature.
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measurement of flow stress in hot plane Strain Compression tests
Materials at High Temperatures, 2006Co-Authors: Malcolm S Loveday, C M Sellars, A J Lacey, G J Mahon, B Roebuck, E J Palmiere, M R Van Der WindenAbstract:AbstractThis Good Practice Guide is applicable to hot (isothermal) plane Strain Compression (PSC) tests at medium to high rates of Strain (10–3 to 102 s–1) at deformation temperatures below the solidus.Guidance is provided on appropriate testpiece geometries and methods of verifying the temperature distribution along the length of the testpiece. Flow diagrams are given showing all the steps that are necessary, including the correction factors that need to be applied for breadth spreading of the testpiece; machine origin and compliance, friction effects and deformational heating. Details are given of the calibration procedures that should be followed to provide traceability to the National Measurement System.The development of the procedure has been supported through experimental tests on type 316 austenitic stainless steel at 1050–1150°C and an aluminium alloy, AA5052, at 300°C to 500°C at Strain rates ranging up to 100 s–1.Technical input to the document has been provided by a steering group comprising a...
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correction of plane Strain Compression data for the effects of inhomogeneous deformation
Materials Science and Technology, 2003Co-Authors: B Kowalski, A J Lacey, C M SellarsAbstract:Plane Strain Compression tests to investigate the effects of heterogeneity of deformation on various initial specimen geometries have been carried out. Equations for correction of nominal Strain and Strain rate to slip line field Strain and Strain rate have been developed and applied to experimental flow stress-Strain data. Investigation of the deformed specimens showed evidence of changing friction conditions during deformation, therefore a simple function allowing friction to change was applied. The corrections eliminate the geometry effect observed in the initial data and lead to modified constitutive equations for flow stress.
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measuring flow stress in hot plane Strain Compression tests
2002Co-Authors: A J Lacey, C M Sellars, Malcolm S Loveday, G J Mahon, B Roebuck, M R Van Der WindenAbstract:This document has been produced to complement the Measurement Good Practice Guide No 3 which describes current best UK practice for measuring hot flow stress in metallic materials using Hot Axisymmetric Compression (HAC). This Guide is applicable to hot (isothermal) plane Strain Compression (PSC) tests at medium to high rates of Strain at deformation temperatures below the solidus. Technical input to the document has been provided by a steering group comprising academic researchers, representatives of industrial users and producers of a wide range of engineering materials. An experimental programme was conducted during the preparation of this document to underpin the procedures in this guide.
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modelling the hot plane Strain Compression test part 1 effect of specimen geometry Strain rate and friction on deformation
Materials Science and Technology, 2001Co-Authors: M S Mirza, C M SellarsAbstract:AbstractThermomechanically coupled finite element analysis of the hot plane Strain Compression test has been carried out to investigate the effect of various test parameters on the measured response and deformation of specimens. The results are presented in a series of papers. In this paper (Part 1), the results of two-dimensional simulations are discussed, evaluating the effects of material type, specimen geometry, Strain rate, and friction on the overall deformation behaviour. The effects of spread and friction are detailed in Part 2, and the effects of asymmetry during the test are detailed in Part 3. The present results show that the local deformation behaviour is independent of the type of material and Strain rate, at least up to 50 s-1. The behaviour, however, depends strongly on friction and initial specimen geometry, with deformation becoming more uniform with decreasing initial specimen thickness, i.e. with increasing tool width w to specimen thickness h ratio. The deformation is conStrained with...
E Lezak - One of the best experts on this subject based on the ideXlab platform.
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plastic deformation behavior of β phase isotactic polypropylene in plane Strain Compression at elevated temperatures part b polymer physics
Journal of Polymer Science, 2008Co-Authors: E Lezak, Z BartczakAbstract:Isotactic polypropylene (iPP) rich in β crystal modification was deformed by plane-Strain Compression at T = 55-100 °C. The evolution of phase structure, morphology, and orientation were studied by DSC, X-Ray, and SEM. The most important deformation mechanisms found were interlamellar slip operating in the amorphous layers, resulting in numerous fine deformation bands and the crystallographic slip systems, including the (110)[001]β chain slip and (110)[$1{\bar {1}}0$]β transverse slip. Shear within deformation bands leads to β[rightward arrow]α solid state phase transformation in contrast to β[rightward arrow]smectic transformation observed at room temperature. Newly formed α crystallites deform with an advancing Strain by crystallographic slip mechanism, primarily the (010)[001]α chain slip. As a result of deformation and phase transformation within deformation bands β lamellae are locally destroyed and fragmented into smaller crystals. Deformation to high Strains, above e = 1, brings further heavy fragmentation of lamellae, followed by fast rotation of crystallites with chain axis towards the direction of flow FD. This process, together with still active crystallographic slip, leads to the final texture with molecular axis of both crystalline β and α phase oriented along FD. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 92-108, 2008
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plastic deformation behavior of β phase isotactic polypropylene in plane Strain Compression at elevated temperatures
Journal of Polymer Science Part B, 2008Co-Authors: E Lezak, Z BartczakAbstract:Isotactic polypropylene (iPP) rich in β crystal modification was deformed by plane-Strain Compression at T = 55-100 °C. The evolution of phase structure, morphology, and orientation were studied by DSC, X-Ray, and SEM. The most important deformation mechanisms found were interlamellar slip operating in the amorphous layers, resulting in numerous fine deformation bands and the crystallographic slip systems, including the (110)[001] β chain slip and (110)[110] β transverse slip. Shear within deformation bands leads to β→α solid state phase transformation in contrast to β→smectic transformation observed at room temperature. Newly formed α crystallites deform with an advancing Strain by crystallographic slip mechanism, primarily the (010)[001] α chain slip. As a result of deformation and phase transformation within deformation bands β lamellae are locally destroyed and fragmented into smaller crystals. Deformation to high Strains, above e = 1, brings further heavy fragmentation of lamellae, followed by fast rotation of crystallites with chain axis towards the direction of flow FD. This process, together with still active crystallographic slip, leads to the final texture with molecular axis of both crystalline β and a phase oriented along FD.
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high Strain deformation of polyethylenes in plane Strain Compression at elevated temperatures
Journal of Applied Polymer Science, 2007Co-Authors: E Lezak, Z BartczakAbstract:The deformation and recovery behavior of several polyethylenes and ethylene-based copolymers with various molecular architectures and a broad range of molecular masses and molecular mass distributions was studied. Because of the differences in the molecular characteristic, this series exhibited a relatively broad range of crystallite sizes and crystallinity levels. The samples were subjected to high Strain Compression under plane-Strain conditions at the elevated temperature of 80°C. The unloading of the compressed samples led to substantial nonelastic recovery of the Strain. The stress–Strain and recovery behavior was related to the molecular parameters. The results confirmed the common deformation scheme with four crossover points related to the activation of subsequent deformation mechanisms, as proposed by Strobl. Although the critical Strains, related to the activation of deformation of the crystalline component, are invariant, the critical Strain of the last point, which is related to the activation of chain disentanglement in the amorphous component, depends on the temperature of deformation. That critical Strain decreases from 1.0 to approximately 0.8–0.9 as the temperature of deformation increases from room temperature to 80°C. This shift results from an increase in the chain mobility with increasing temperature, and this makes modification of the molecular network through chain disentanglements easier. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 105: 14–24, 2007
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plastic deformation of the γ phase isotactic polypropylene in plane Strain Compression at elevated temperatures
Macromolecules, 2007Co-Authors: E Lezak, Z BartczakAbstract:Plastic deformation behavior of iPP homopolymer crystallized exclusively in the γ modification was studied. Samples of γ-iPP were obtained by isothermal crystallization under pressure of 200 MPa. Deformation experiments in plane−Strain Compression were performed in the temperature range of 55−100 °C. Samples of γ-iPP demonstrated higher modulus, higher yield stress, and flow stress, yet slightly lower ultimate Strain comparing to α-iPP in the entire range of temperature studied. During plastic deformation numerous fine shear bands, initiated by the interlamellar shear of the amorphous layers, start to develop already at the yield point. Their propagation across the sample causes a limited destruction of γ lamellae oriented perpendicularly to the direction of the band. Destroyed fragments of crystallites partially reconstruct into either mesophase (smectic) domains or crystals of α phase, depending on the deformation temperature. Mesophase is produced upon deformation at room temperature, while at 55 °C an...
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plastic deformation behavior of β phase isotactic polypropylene in plane Strain Compression at room temperature
Polymer, 2006Co-Authors: E Lezak, Z Bartczak, Andrzej GaleskiAbstract:Abstract Isotactic polypropylene (iPP) rich in β crystal modification (constituting 92% of crystalline phase) was deformed by the plane-Strain Compression with constant true Strain rate, at room temperature. The evolution of phase structure, morphology and orientation was studied by DSC, X-ray and SEM. The deformation sequence and the active deformation mechanisms were found out. The most important mechanisms were interlamellar slip operating in the amorphous layers, resulting in numerous fine deformation bands due to localization of deformation and the crystallographic slip systems, including the (110)[001] chain slip and (110)[1 1 ¯ 0] transverse slip. Shear within deformation bands leads to β → smectic and β → α solid state phase transformations. At room temperature the β → smectic transformation appeared to be the primary transformation, yielding the oriented smectic phase with high concentration of 19 wt.% at the true Strain of e = 1.49. The β → α yields only about 4 wt.% of new α-phase at the same Strain. As a result of the deformation and phase transformation within numerous fine deformation bands β-lamellae are locally destroyed and fragmented into smaller crystals. Another deformation mechanism is the cooperative kinking of lamellae, leading to their reorientation and formation of a chevron-like lamellar arrangement. At high Strains, above e = 1, an advanced crystallographic slip and high stretch of amorphous material due to interlamellar shear bring further heavy fragmentation of lamellar crystals, earlier fragmented partially by deformation bands. This fragmentation is followed by fast rotation of small unconStrained crystallites with chain axis towards the direction of flow, FD. This process leads to development of the final texture of the highly deformed β-iPP with molecular axis of both crystalline and smectic phases oriented along FD.
Fumio Tatsuoka - One of the best experts on this subject based on the ideXlab platform.
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effects of geosynthetic reinforcement type on the strength and stiffness of reinforced sand in plane Strain Compression
Soils and Foundations, 2007Co-Authors: Warat Kongkitkul, Daiki Hirakawa, Fumio Tatsuoka, Taro KanemaruAbstract:The effects of geosynthetic reinforcement type on the strength and stiffness of reinforced sand were evaluated by performing a series of drained plane Strain Compression tests on large sand specimens. The reinforcement type is described in terms of the degree of unification of the constituting components (for geocomposites) as well as the tensile strength and stiffness, the covering ratio and others (for geocomposites and geogrids). Sand specimens reinforced with different geosynthetic reinforcement types exhibited significantly different reinforcing effects. A geocomposite made of a woven geotextile sheet sandwiched firmly with two sheets of non-woven geotextile, having a 100% effective covering ratio, exhibited reinforcing effects higher than typical stiff and strong geogrids. With some geocomposite types, the reinforcing effects increase substantially by better unifying longitudinally arranged stiff and strong yarns and non-woven geotextile sheets. When fixed firm to the yarns, the non-woven geotextile sheets function like the transversal members of a geogrid by locally transmitting load activated by interaction with the backfill to the yarns. These geocomposites can exhibit reinforcing effects equivalent to those with stiff and strong geogrids. Local Strain fields of the specimens are presented to show that, for reinforced sand, the peak stress state reached is always associated with the development of shear band(s) in the sand and a higher peak strength is achieved when the Strain localisation starts at a larger global axial Strain due to better reinforcing effects.
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rate dependent load Strain behaviour of geogrid arranged in sand under plane Strain Compression
Soils and Foundations, 2007Co-Authors: Warat Kongkitkul, Fumio Tatsuoka, Daiki HirakawaAbstract:A number of previous experimental studies showed that polymer geogrid reinforcement as well as sand exhibit significantly rate-dependent behaviour. The viscous properties of polymer geogrids and Toyoura sand were independently evaluated by changing stepwise the Strain rate as well as performing sustained loading and load/stress relaxation tests during otherwise monotonic loading in, respectively, tensile loading tests and drained plane Strain Compression (PSC) tests. The viscous properties of the two types of material were separately formulated in the same framework of non-linear three-component rheology model. The viscous response of geogrid-reinforced sand in PSC is significant, controlled by viscous properties of geogrid and sand. Local Strain distributions in the reinforced sand specimen were evaluated by photogrametric analysis and used to determine the time history of the tensile Strain in the geogrid. The time history of tensile load activated in the geogrid during sustained loading of reinforced sand specimen was deduced by analysing the measured time history of geogrid Strain by the non-linear three-component model. It was found that the tensile load in the geogrid reinforcement arranged in a sand specimen subjected to fixed boundary loads could decrease with time. In that case, the possibility of creep rupture of geogrid is very low.
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FEM SIMULATION OF THE VISCOUS EFFECTS ON THE STRESS-Strain BEHAVIOUR OF SAND IN PLANE Strain Compression
Soils and Foundations, 2006Co-Authors: Mohammed Saiful Alam Siddiquee, Fumio Tatsuoka, Tadatsugu TanakaAbstract:A stress-Strain model called TESRA (Temporary Effects of Strain Rate and Acceleration), described in a non-linear three-component framework, has been proposed to simulate the effects of viscous property on the stress-Strain behaviour observed in drained plane Strain Compression (PSC) tests on clean sands. According to the TESRA model, the current viscous stress component is obtained by integrating for a given history of irreversible Strain increments of viscous stress component that developed by respective instantaneous irrecoverable Strain increment and its rate and have decayed with an increase in the irreversible Strain until the present. The TESRA model was implemented into a generalized elasto-plastic isotropic Strain-hardening non-linear FE code. The integration scheme to obtain the viscous and inviscid stress components according to the TESRA model in FEM analysis needs some specific considerations including the relevant choice of the suitable rate parameter. The shear stress—shear (or axial) Strain—time relations from five drained PSC tests on saturated Toyoura sand and air-dried Hostun sand were successfully simulated by the FE code embedded with the TESRA model. It is shown that the FE code can simulate the time-dependent stress-Strain behaviour of sand accurately without spending any significant extra computational time or storage. The results of simulation using one element and multi-element are essentially the same.
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plane Strain Compression behaviour of geogrid reinforced sand and its numerical analysis
Soils and Foundations, 2000Co-Authors: Fangle Peng, Fumio Tatsuoka, Daiki Hirakawa, Nozomu Kotake, Tadatsugu TanakaAbstract:Plane Strain Compression tests were performed on large specimens that were either unreinforced or reinforced with 6 or 11 layers of geogrid, both 57.0 cm in height and 24.4 cm×21.4 cm in cross-section. It is shown that the effects of covering ratio for each grid layer is much more important than the total tensile stiffness of grid within the limits of the test conditions in this study. Numerical analysis of the test results by a plane Strain non-linear elasto-plastic FEM was performed considering Strain localisation as well as anisotropic stress-Strain behaviour of sand and interface properties. The geogrid was modelled as a planar reinforcement. Not only the pre-peak stress-Strain behaviour of the unreinforced and reinforced specimens, but also the peak strength, post-peak behaviour and dilatancy characteristics from the FEM analysis all compared well with those from the physical tests. The effects of reinforcement rigidity and covering ratio were also well simulated. The relationship between the reinforcement covering ratio in the physical tests and the equivalent interface friction angle for the FEM analysis that provides the same reinforcing effects is presented. The mechanism of tensile-reinforcing is analysed based on local stress paths within the reinforced sand obtained from the FEM analysis.
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an insight into the failure of reinforced sand in plane Strain Compression by fem simulation
Soils and Foundations, 1999Co-Authors: Nozomu Kotake, Tadatsugu Tanaka, Mohammed Saiful Alam Siddiquee, Fumio Tatsuoka, Hiromoto YamauchiAbstract:An FEM simulation of plane Strain Compression tests of dense Toyoura sand reinforced with reinforcement having a wide range of stiffness is described. Strain localisation is taken into account by modelling a shear band having a specific thickness and specific Strain-softening properties determined based on experimental results. Global and local behaviour of the unreinforced and reinforced sand observed in plane Strain Compression tests are properly simulated.
Qing Liu - One of the best experts on this subject based on the ideXlab platform.
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hot deformation behavior and microstructure of aa2195 alloy under plane Strain Compression
Materials Characterization, 2017Co-Authors: Qingbo Yang, Xinzhu Wang, Zanhui Deng, Zhihong Jia, Zhiqing Zhang, Guangjie Huang, Qing LiuAbstract:Abstract The hot deformation behavior of Al-Cu-Li alloy was studied under plane Strain Compression in the temperature range of 400–500 °C and Strain rate of 0.01–10 s − 1 . The related microstructure was studied by optical microscopy, electron back-scattered diffraction and transmission electron microscope. The results showed that the stress decreased significantly with the increase of temperature and decrease of Strain rate. However, stress increase was found after peak stress at Strain rate of 0.01 s − 1 and deformation temperature 440–500 °C. Constitutive equation based on the hyperbolic sine equation was established and the apparent activation energy of plane Strain Compression was estimated to be 226.7 KJ/mol. Precipitates decreased and finally disappeared with decreasing Z value, having an impact on the softening mechanism. Plate-shaped particles and precipitate zones reStrained the proceeding of dynamic recovery but increased store energy for discontinuous dynamically recrystallization nuclei. Therefore, recrystallization nuclei more obviously occurred in the sample with higher ln Z value than the one with lower ln Z value at close ln Z value. The microstructure of all deformed specimens was composed of elongated grains and new quasi-equiaxed grains. However, the basic deformation mechanism was dynamic recovery. The mechanism of recrystallization nuclei transformed discontinuous dynamic recrystallization into continuous dynamic recrystallization with the decreasing Z values.
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crystallographic analysis on the activation of multiple twins in rolled az31 mg alloy sheets during uniaxial and plane Strain Compression
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2016Co-Authors: Renlong Xin, Changhong Ding, Changfa Guo, Qing LiuAbstract:Abstract It is well known that the activation and interception of multiple twins in Mg alloys largely influence microstructural evolution and Strain hardening behavior. However, the crystallographic conditions for the activation of multiple twins and their variant selection have not been well understood. Therefore, the present work was conducted in attempt to find some trends such as grain orientation, Schmid factor and geometric compatibility factor on the activation and variant selection of multiple twins in both uniaxial Compression (UC) and plane Strain Compression (PSC). The results showed that most of the twins in single twin grains strictly followed Schmid law. For the activation of multiple twin variants inside grains and cross-boundary twins, the local Strain compatibility between the connected twins was also important for variant selection. Because of the conStraint along the c -axis, twinning activation was suppressed in PSC compared to UC. In general, the variant selection of twinning was more likely affected by local Strain compatibility in PSC than that in UC. These experimental results may shed light on the development of advanced physics-based simulation models.
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a comparative study between uniaxial Compression and plane Strain Compression of mg 3al 1zn alloy using experiments and simulations
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2014Co-Authors: Adrien Chapuis, Bingshu Wang, Qing LiuAbstract:Abstract Magnesium anisotropic behavior is enhanced by different deformations paths and modes. The mechanical anisotropy during plastic deformation of a Mg–3Al–1Zn magnesium alloy was examined by uniaxial Compression (UC) and plane Strain Compression (or channel-die CD) at room temperature. The mechanical behavior and the observed microtextures were compared with the predictions obtained from different crystal plasticity models. A hot rolled AZ31 magnesium alloy plate with a strong basal texture was stressed along four different directions to initiate different deformation mechanisms. In both UC and CD, the Compression along the transverse direction generated mainly {10−12} extension twins, while Compression along the normal direction (Z=ND) was initially accommodated by pyramidal 〈c+a〉 slip followed by contraction twinning. During Compression at 45° of the normal direction to the transverse direction, both slip and twinning took part in the deformation. The sample compressed in CD along the rolling direction and with the normal direction conStrained was deformed by prismatic slip and tension twinning. It was found that basal slip was an important deformation mechanism in all the samples. Simulations were made with different models, and the simulated flow stresses were higher in CD than that in UC, but slightly underestimated in case of uniaxial Compression. Modeling also corroborated higher {10−11} Compression twinning activity in CD than that in UC, and that Compression twinning resulted in a decrease in flow stress in CD. To fit with the experimental flow stresses, it was necessary to take into account an additional hardening caused by twin boundaries. In our model, the {10−12} twin boundaries were estimated to increase the critical resolved shear stress (CRSS) of prismatic slip by about 30%. However, twin induced hardening on pyramidal 〈c+a〉 and basal slip of about 10% is also necessary if contraction twinning do not soften the material.
