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Youwen Yang - One of the best experts on this subject based on the ideXlab platform.
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microstructural characterization and evolution mechanism of Adiabatic Shear Band in a near beta ti alloy
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2011Co-Authors: Youwen Yang, Fang Jiang, B M Zhou, X M Li, Hui Zheng, Q M ZhangAbstract:Abstract The Adiabatic Shear Band (ASB) was obtained by split Hopkinson pressure bar (SHPB) technique in the hat-shaped specimen of a near beta-Ti alloy. The microstructure and the phase transformation within the ASB were investigated by means of TEM. The results show that the elongated subgrains with the width of 0.2–0.4 μm have been observed in the Shear Band boundary, while the microstructure inside the ASB consists of fine equiaxed subgrains that are three orders of magnitude smaller than the grains in the matrix. The β → ω(althermal) phase transformation has been observed in the ASB, and further analysis indicates that the Shear Band offers thermodynamic and kinetic conditions for the ω(althermal) phase formation and the high alloying of this alloy is another essential factor for this transformation to take place. The thermo-mechanical history during the Shear localization is calculated. The rotational dynamic recrystallization (RDR) mechanism is used to explain the microstructure evolution mechanism in the Shear Band. Kinetic calculations indicate that the recrystallized fine subgrains are formed during the deformation and do not undergo significant growth by grain boundary migration after deformation.
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observation of the microstructure in the Adiabatic Shear Band of 7075 aluminum alloy
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2010Co-Authors: Dongjie Li, Youwen Yang, Hui Zheng, T Xu, Q M ZhangAbstract:Abstract A considerable amount of Adiabatic Shear Bands (ASBs) were obtained by means of the thick-walled cylinder (TWC) external explosive collapse technique. Two types of Shear Bands with different morphologies are distinguished on the cross-section of the tube, which are called deformed Band and transformed Band, respectively. Cracks are confirmed to develop from the transformed Bands rather than the deformed Band. Transmission electron microscopy (TEM) investigation indicates that ultrafine grains, with average size less than 100 nm, are produced at the center of the transformed Band. At the edge of the transformed Band the grains are elongated in the Shearing direction. The grains in the matrix are two orders of magnitude larger than those in the transformed Band. The precipitation within the Shear Band and the matrix is quite different. Calculation estimates that the temperature in the Shear Band exceeds the recrystallization temperature of the 7075 aluminum alloy. It is proposed that dynamic recrystallization occurs in the transformed Band and produces the ultrafine grains. Microhardness test results show that the transformed Band is much “harder” than the matrix.
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microstructure evolution in Adiabatic Shear Band in fine grain sized ti 3al 5mo 4 5v alloy
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2008Co-Authors: Bin Wang, Youwen YangAbstract:Abstract Dynamic testing of Ti–3Al–5Mo–4.5V (TC16) alloy was carried out in a hat-shaped specimen by a split Hopkinson pressure bar (SHPB) at ambient temperature. The microstructure and phase transformation in Adiabatic Shear Band (ASB) produced in TC16 alloy were investigated by means of optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). ASB in TC16 alloy is a “white” Band of width about 13 μm. The elongated cell structures of width about 0.2–0.5 μm with thick dislocation exist in the boundary of the Shear Band. Results suggest that the fine equiaxed grains with α-phase and α″-phase coexist in the Shear Band. The “white” Band is a transformation Band. Calculation indicates that the maximum temperature within ASB is about 1069 K. The phase transformation and the microstructure evolution within ASB in TC16 alloy are explained.
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microstructure evolution in Adiabatic Shear Band in α titanium
Journal of Materials Science, 2006Co-Authors: Youwen Yang, Bin WangAbstract:The microstructure and microtexture of Adiabatic Shear Bands (ASBs) on the titanium side of a titanium/mild steel explosive cladding interface are investigated by means of optical microscopy (OM), scanning electron microscopy/electron back-scattered diffraction (SEM/EBSD) and transmission electron microscopy (TEM). Highly elongated subgrains and fine equiaxed grains with low dislocation density are observed in the ASBs. Recrystallization microtextures (28°, 54°, 0°), (60°, 90°, 0°) and (28°, 34°, 30°) are formed within ASBs. The grain boundaries within ASBs are geometrical necessary boundaries (GNBs) with high-angles. Based on the relations between temperature and the engineering Shear strain, the temperature in the ASBs is estimated to be about 776–1142 K (0.4–0.6 T m). The rotation dynamic recrystallization (RDR) mechanism is employed to describe the kinetics of the nano-grains’ formation and the recrystallized process within ASBs. The small grains within ASBs are formed during the deformation and do not undergo significant growth by grain boundary migration after deformation.
Shukui Li - One of the best experts on this subject based on the ideXlab platform.
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effect of initial temperature on dynamic recrystallization of tungsten and matrix within Adiabatic Shear Band of tungsten heavy alloy
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2011Co-Authors: Jia Yang, Shukui LiAbstract:Abstract Uniaxial dynamic compression tests were performed on tungsten heavy alloys (WHAs) at different temperatures. The microstructure evolution of tungsten grains and matrix within Adiabatic Shear Band (ASB) was investigated. With the initial temperature decreased, the width of elongated subgrain observed in both tungsten grains and matrix shows a decreasing tendency, and the dynamic recrystallization (DRX) process within ASB is evidently suppressed and delayed at cryogenic temperatures. Compared with tungsten grain, the DRX of matrix is earlier and more sufficient, and the observed subgrain of matrix is much finer. No twins were observed during DRX of tungsten grains at various temperatures. However, secondary slip micro Bands were observed within the elongated subgrain of matrix at −80 °C, with the angle between the micro Bands and original subgrain ranging from 38° to 45°, and twins were observed in matrix at a lower temperature of −140 °C.
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effect of fibrous orientation on dynamic mechanical properties and susceptibility to Adiabatic Shear Band of tungsten heavy alloy fabricated through hot hydrostatic extrusion
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2008Co-Authors: Shukui LiAbstract:The tungsten heavy alloys (WHAs) with fibrous grains were obtained by hot-hydrostatic extrusion at 950 °C with plastic deformation ratio of 75%. Dynamic mechanical behaviors under uniaxial dynamic compression were systematically investigated with the angles between the loading direction and the extruding direction being 0°, 45° and 90°. The testing results show obvious difference in dynamic behaviors and susceptibility to Adiabatic Shear Band (ASB) for different specimens. In the 0° specimens, no localized flow is observed. The 45° specimens exhibit slight localized Shearing. In the 90° specimens, localized ASB was firstly observed at an angle of 45° with respect to the fibrous orientation followed by cracking, which is greatly desirable for kinetic energy penetration applications. Microstructure analyses reveal that the high susceptibility to ASB of the 90° specimens result from Adiabatic temperature rising during dynamic loading and reduced strain hardening caused by the special micro-strained condition and fiber distribution.
Piotr Perzyna - One of the best experts on this subject based on the ideXlab platform.
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Analysis of the influence of various effects on criteria for Adiabatic Shear Band localization in single crystals
Acta Mechanica, 1998Co-Authors: Piotr Perzyna, K KorbelAbstract:The paper aims at the investigation of the influence of various effects on criteria for Shear Band localization in inelastic single crystals. This investigation is based on an analysis of acceleration waves and takes advantage of a notion of the instantaneous Adiabatic acoustic tensor. Particular attention is focussed on the analysis of the effects as follows: (i) spatial covariance and plastic spin; (ii) thermomechanical coupling; (iii) non-Schmid; (iv) evolution of substructure; (v) nondissipative thermal term; (vi) cooperative phenomena (synergetic). The theory of thermoviscoplasticity of inelastic single crystals is presented within a framework of the rate type covariance constitutive structure with a finite set of the internal state variables. By assuming that the mechanical relaxation time is equal to zero the thermo-elasto-plastic (rate independent) response of single crystals is accomplished. An Adiabatic inelastic flow process of the single crystal is formulated and investigated. Symmetric double slip and single slip processes are considered. The formulation of macroscopic Adiabatic Shear Bands is investigated. The criteria for Adiabatic Shear Band localization for a single slip process are presented in exact analytical form. For a symmetric double slip process these criteria are estimated numerically. The discussion of the influence of various effects is presented, and the comparison of the results obtained with available experimental observations is given.
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Adiabatic Shear Band localization in single crystals under dynamic loading processes
Archives of Mechanics, 1997Co-Authors: M K Duszekperzyna, K Korbel, Piotr PerzynaAbstract:THE MAIN OBJECTIVE of the paper is the investigation of Adiabatic Shear Band localization phenomena in inelastic single crystals under dynamic loading processes. In the first part, a rate-dependent plastic model of single crystals is developed within the thermodynamic framework of the rate-type covariance constitutive structure. This model takes account of the effects as follows: (i) influence of covariance terms, lattice rotations and plastic spin; (ii) thermomechanical coupling; (iii) evolution of the dislocation substructure. An Adiabatic process is formulated and examined. The relaxation time is used as a regularization parameter. The viscoplastic regularization assures the stable integration algorithm by using the finite element method. It has been shown that the evolution problem (the initial-boundary value problem) for rate-dependent plastic model of single crystals is well posed. The second part is devoted to the investigation of criteria of localization of plastic deformation in both single slip and symmetric double slip processes. The Adiabatic Shear Band formation in elastic-plastic rate-independent single crystals during dynamic loading processes is investigated. The critical value of the strain hardening rate and the misalignment of the Shear Band from the active slip systems in the crystal's matrix have been determined. Particular attention is focused on the investigation of synergetic effects. Calculations have been obtained for aluminum single crystals. The results obtained are compared with available experimental observations.
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Adiabatic Shear Band localization of inelastic single crystals in symmetric double-slip process
Archive of Applied Mechanics, 1996Co-Authors: M. K. Duszek-perzyna, Piotr PerzynaAbstract:The main objective of the present paper is the development of a viscoplastic regularization procedure valid for an Adiabatic dynamic process for multi-slips of single crystals. The next objective is to focus attention on the investigation of instability criteria, and particularly on Shear Band localization conditions. To achieve this aim, an analysis of acceleration waves is given, and advantage is taken of the notion of the instantaneous Adiabatic acoustic tensor. If zero is an eigenvalue of the acoustic tensor, then the associated discontinuity does not propagate, and one speaks of a stationary discontinuity. This situation is referred to as the ‘strain localization condition’, and corresponds to a loss of hyperbolicity of the dynamical equations. It has been proved that for an, Adiabatic process of rate-dependent (elastic-viscoplastic) crystal, the wave speed of discontinuity surface always remains real and different from zero. It means that for this case the initial-value problem is well-posed. However, for an Adiabatic process of rate-independent(elastic-plastic) crystal, the wave speed of discontinuity surface can be equal zero. Then the necessary condition for a localized plastic deformation along the Shear Band to be formed is as follows: the determinant of the instantaneous Adiabatic acoustic tensor is equal to zero. This condition for localization is equivalent to that obtained by using the standard bifurcation method. Based on this idea, the conditions for Adiabatic Shear Band localization of plastic deformation have been investigated for single crystals. Particular attention has been focused on the discussion of the influence of thermal expansion, thermal plastic, softening and spatial covariance effects on Shear Band localization criteria for a planar model of an f.c.c. crystal undergoing symmetric primary-conjugate double slip. The results obtained have been compared with available experimental observations. Finally, it is noteworthy that the viscoplasticity regularization procedure can be used in the developing of an unconditionally stable numerical integration algorithm for simulation of Adiabatic inelastic flow processes in ductile single crystals, cf. [21].
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analysis of the influence of anisotropy effects on Adiabatic Shear Band localization phenomena
1995Co-Authors: Piotr PerzynaAbstract:The problem of strain induced anisotropy associated with the development of crystallographic textures has been recently investigated in many scientific centres. The main objective of the present paper is the analytical investigation of the influence of anisotropy effects generated by plastic spin*, plastic non-normality and kinematic hardening on criteria for Adiabatic Shear Band localization and the discussion of cooperative phenomena.
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instability phenomena and Adiabatic Shear Band localization in thermoplastic flow processes
Acta Mechanica, 1994Co-Authors: Piotr PerzynaAbstract:The main objective of the paper is the development of the viscoplastic regularization procedure valid for a broad class of thermodynamic plastic flow processes in damaged solids. The additional aim is to investigate instability phenomena and Adiabatic Shear Band localization criteria when spatial covariance, thermomechanical coupling, strain induced anisostropy and micro-damage softening effects are taken into consideration. This investigation is based on an analysis of acceleration waves and takes advantage of a notion of the instantaneous Adiabatic acoustic tensor. In the first part of the paper the formulation of an inelastic flow process is given and particular attention is focussed on the thermomechanical coupling effects. The thermodynamic theory of elastic-viscoplastic damaged solids is presented within a framework of the rate type covariance material structure with a finite set of the internal state variables. A notion of covariance is understood in the sense of invariance under an arbitrary spatial diffeomorphism. Rate sensitivity effect is introduced by the assumption of the viscoplastic overstress conception. A notion of a relaxation time has been used to control the description of mechanical as well as thermal disturbances. By the assumption that the mechanical relaxation time is equal to zero the thermo-elastic-plastic (rate independent) response of the damaged material is accomplished. In the second part of the paper the existence of a solution to the initial-boundary value problem is examined and its stability property is investigated based on the application of nonlinear semi-group methods and an analysis of continuity of evolution operators. For an Adiabatic process the investigation of acceleration waves is given. The determination of eigenvalues of the appropriate acoustic tensor is presented. This helps to assess the well-posedness of the initial-value problems which describe the thermodynamic plastic flow processes. Differences for two constitutive assumptions, namely for rate dependent and rate independent responses, are examined. In the case of an Adiabatic process and elastic-viscoplastic response of a material the conditions for the existence, uniqueness and well-posedness of the initial value problem have been investigated.
Bin Wang - One of the best experts on this subject based on the ideXlab platform.
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microstructural evolution in Adiabatic Shear Band in the ultrafine grained austenitic stainless steel processed by multi axial compression
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2014Co-Authors: Bingfeng Wang, Bin Wang, Shiteng ZhaoAbstract:Abstract Adiabatic Shear Bands play the most important role in the deformation and failure of high strength AISI 201 austenitic stainless steel. The microstructure and microtexture of the Adiabatic Shear Band in ultrafine-grained stainless steel are investigated by means of optical microscopy, TEM and EBSD. The Shear Bands can be generated at about 54 μs after the true flow stress reaches the peak value of about 1135 MPa. The width of the Shear Bands is about 9 μm, and the grains sizes 50–200 nm in the boundary of the Shear Band are elongated along the Shear direction; the grain subdivision on approaching the Shear Band can be observed, and the core of the Shear Band consists of recrystallized equiaxed grains (sizes 30–80 nm) with new microtextures and the ultrafine grains with deformed microtextures and with high dislocation density. The grain boundaries in the Adiabatic Shear Band are geometrical necessary boundaries with high-angles. The calculated temperature in the Shear Band is estimated to reach 0.58 T m (968 K). It takes 7 μs for the Shear Band to cool down from 968 K to the room temperature when the Shear localization ceases, and the cooling strain rate is calculated as high as 9.6×10 7 K/s. Kinetic calculations indicate that during the deformation process, the recrystallized nanosized grains can be formed in the Shear Band by way of the subgrain boundaries rotation when the subgrains׳ sizes are lower than 80 nm or the temperature in the Shear Band is higher than 0.5 T m (834 K), and they do not undergo significant growth by grain boundary migration at the cooling stage. These results indicate that the microstructure development within Shear Band is controlled by both dynamic recovery and rotational dynamic recrystallization.
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Adiabatic Shear Band in a ti 3al 5mo 4 5v titanium alloy
Journal of Materials Science, 2008Co-Authors: Bin WangAbstract:An investigation has been carried out on the Adiabatic Shear Band (ASB) in a Ti-3Al-5Mo-4.5V (TC16) alloy deformed at high strain rate by a split Hopkinson pressure bar (SHPB). ASB in TC16 alloy is a “white” Band with a width of about 13 μm. Microhardness of the ASB is larger than that of the matrix. The elongated cell structures of width about 0.2–0.5 μm with thick dislocation exist in the boundary of the Shear Band. Results suggest that the fine equiaxed grains with α-phase and α″-phase coexist in the Shear Band. The “white” Band is a transformation Band. Calculation of the Adiabatic temperature rise indicates that the maximum temperature within ASB is about 1,069 K that is above the phase transformation temperature. Finally, formation of an ASB in the TC16 alloy and its microstructure evolution are described.
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microstructure evolution in Adiabatic Shear Band in fine grain sized ti 3al 5mo 4 5v alloy
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2008Co-Authors: Bin Wang, Youwen YangAbstract:Abstract Dynamic testing of Ti–3Al–5Mo–4.5V (TC16) alloy was carried out in a hat-shaped specimen by a split Hopkinson pressure bar (SHPB) at ambient temperature. The microstructure and phase transformation in Adiabatic Shear Band (ASB) produced in TC16 alloy were investigated by means of optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). ASB in TC16 alloy is a “white” Band of width about 13 μm. The elongated cell structures of width about 0.2–0.5 μm with thick dislocation exist in the boundary of the Shear Band. Results suggest that the fine equiaxed grains with α-phase and α″-phase coexist in the Shear Band. The “white” Band is a transformation Band. Calculation indicates that the maximum temperature within ASB is about 1069 K. The phase transformation and the microstructure evolution within ASB in TC16 alloy are explained.
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microstructure evolution in Adiabatic Shear Band in α titanium
Journal of Materials Science, 2006Co-Authors: Youwen Yang, Bin WangAbstract:The microstructure and microtexture of Adiabatic Shear Bands (ASBs) on the titanium side of a titanium/mild steel explosive cladding interface are investigated by means of optical microscopy (OM), scanning electron microscopy/electron back-scattered diffraction (SEM/EBSD) and transmission electron microscopy (TEM). Highly elongated subgrains and fine equiaxed grains with low dislocation density are observed in the ASBs. Recrystallization microtextures (28°, 54°, 0°), (60°, 90°, 0°) and (28°, 34°, 30°) are formed within ASBs. The grain boundaries within ASBs are geometrical necessary boundaries (GNBs) with high-angles. Based on the relations between temperature and the engineering Shear strain, the temperature in the ASBs is estimated to be about 776–1142 K (0.4–0.6 T m). The rotation dynamic recrystallization (RDR) mechanism is employed to describe the kinetics of the nano-grains’ formation and the recrystallized process within ASBs. The small grains within ASBs are formed during the deformation and do not undergo significant growth by grain boundary migration after deformation.
Matthew A Davies - One of the best experts on this subject based on the ideXlab platform.
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on repeated Adiabatic Shear Band formation during high speed machining
International Journal of Plasticity, 2002Co-Authors: Timothy J Burns, Matthew A DaviesAbstract:Abstract We compare the repeated Adiabatic Shear Band formation that takes place at sufficiently large cutting speeds in a number of materials during high-speed machining operations with the more well-known formation of a single Shear Band that often takes place at sufficiently large strain rates in dynamic torsion tests on these materials. We show that there are several major differences in the physics of the two deformation processes. In particular, the Shear stress in machining over the tool-material contact length is not even approximately homogeneous. Additionally, in high-speed machining, the material flow can become convection-dominated, so that the tool can “outrun” the thermal front generated in the workpiece material by the high-strain-rate cutting process. We demonstrate by means of a one-dimensional continuum model that these differences can lead to repeated oscillations in the plastic flow of the workpiece material during high-speed machining, leading to the repeated formation of Adiabatic Shear Bands.
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On repeated Adiabatic Shear Band formation during high-speed machining ☆
International Journal of Plasticity, 2002Co-Authors: Timothy J Burns, Matthew A DaviesAbstract:Abstract We compare the repeated Adiabatic Shear Band formation that takes place at sufficiently large cutting speeds in a number of materials during high-speed machining operations with the more well-known formation of a single Shear Band that often takes place at sufficiently large strain rates in dynamic torsion tests on these materials. We show that there are several major differences in the physics of the two deformation processes. In particular, the Shear stress in machining over the tool-material contact length is not even approximately homogeneous. Additionally, in high-speed machining, the material flow can become convection-dominated, so that the tool can “outrun” the thermal front generated in the workpiece material by the high-strain-rate cutting process. We demonstrate by means of a one-dimensional continuum model that these differences can lead to repeated oscillations in the plastic flow of the workpiece material during high-speed machining, leading to the repeated formation of Adiabatic Shear Bands.
