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Adiabatic Shear Band

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Youwen Yang – 1st expert on this subject based on the ideXlab platform

  • 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, 2011
    Co-Authors: Youwen Yang, Fang Jiang, B M Zhou, X M Li, Hui Zheng, Q M Zhang

    Abstract:

    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.

  • observation of the microstructure in the Adiabatic Shear Band of 7075 aluminum alloy
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2010
    Co-Authors: Dongjie Li, Youwen Yang, Hui Zheng, T Xu, Q M Zhang

    Abstract:

    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.

  • 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, 2008
    Co-Authors: Bin Wang, Youwen Yang

    Abstract:

    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.

Shukui Li – 2nd expert on this subject based on the ideXlab platform

  • 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, 2011
    Co-Authors: Jia Yang, Shukui Li

    Abstract:

    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.

  • 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, 2008
    Co-Authors: Shukui Li

    Abstract:

    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 – 3rd expert on this subject based on the ideXlab platform

  • Analysis of the influence of various effects on criteria for Adiabatic Shear Band localization in single crystals
    Acta Mechanica, 1998
    Co-Authors: Piotr Perzyna, K Korbel

    Abstract:

    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.

  • Adiabatic Shear Band localization in single crystals under dynamic loading processes
    Archives of Mechanics, 1997
    Co-Authors: M K Duszekperzyna, K Korbel, Piotr Perzyna

    Abstract:

    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.

  • Adiabatic Shear Band localization of inelastic single crystals in symmetric double-slip process
    Archive of Applied Mechanics, 1996
    Co-Authors: M. K. Duszek-perzyna, Piotr Perzyna

    Abstract:

    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].