• Title/Summary/Keyword: shear localization

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SENSITIVITY OF SHEAR LOCALIZATION ON PRE-LOCALIZATION DEFORMATION MODE

  • Kim, Kwon--Hee-
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 1992.03a
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    • pp.83-102
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    • 1992
  • As shear localization is observed in different deformation modes, an attempt is made to understand the conditions for shear localization in general deformation modes. Most emphasis in put upon the effects of pre-localization deformation mode on the onset of shear localization and all the other well-recognized effects of subtle constitutive features and imperfection sensitivity studied elsewhere are not investigated here. Rather, an approximate perturbation stability analysis is performed for simplified isotropic rigid-plastic solids subjected to general mode of homogeneous deformation. Shear localization is possible in any deformation mode if the material has strain softening. The incipient rate of shear localization and shear plane orientations are strongly dependent upon the pre-localization deformation mode. Significant strain softening is necessary for shear localization in homogeneous axisymmetric deformation modes while infinitesimal strain softening is necessary for shear localization in plane strain deformation mode. In any deformation mode, there are more than one shear plane orientation. Except for homogeneous axisymmetric deformation modes, there are two possible shear plane orientations with respect to the principal directions of stretching. Some well-known examples are discussed in the light of the current analysis.

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A Study of Localization for Adiabatic Shear Band in WHA(Tungsten Heavy Alloy) (텅스텐 중합금의 단열전단밴드 형성 및 국부화에 대한 연구)

  • Hwang, Doo-Son;Hong, Sung-In
    • Journal of the Korean Society of Propulsion Engineers
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    • v.11 no.6
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    • pp.18-25
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    • 2007
  • In a plastic metal forming of thermally rate-sensitive material, the localized shear band stems from evolution of a narrow region in which intensive plastic flow occurs. And it give rise to fatal fracture with plastic instability. The objectives of this study are to investigate the localization behavior by using numerical method and predict the failure for WHA(Tungsten Heavy Alloy). In this work, the implicit finite difference scheme is used because of the advantage about convergence and the numerical stability. This study is based on an analysed material with hardening as well as thermally softening behavior which includes isotropic strain hardening and observed the extension of localization within shear band according to material properties.

Adaptive Mesh Refinement Procedure for Shear Localization Problems

  • Kim, Hyun-Gyu;Im, Se-Young
    • Journal of Mechanical Science and Technology
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    • v.20 no.12
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    • pp.2189-2196
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    • 2006
  • The present work is concerned with the development of a procedure for adaptive computations of shear localization problems. The maximum jump of equivalent strain rates across element boundaries is proposed as a simple error indicator based on interpolation errors, and successfully implemented in the adaptive mesh refinement scheme. The time step is controlled by using a parameter related to the Lipschitz constant, and state variables in target elements for refinements are transferred by $L_2$-projection. Consistent tangent moduli with a proper updating scheme for state variables are used to improve the numerical stability in the formation of shear bands. It is observed that the present adaptive mesh refinement procedure shows an excellent performance in the simulation of shear localization problems.

Numerical simulations of localization of deformation in quasi-brittle materials within non-local softening plasticity

  • Bobinski, J.;Tejchman, J.
    • Computers and Concrete
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    • v.1 no.4
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    • pp.433-455
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    • 2004
  • The paper presents results of FE-calculations on shear localizations in quasi-brittle materials during both an uniaxial plane strain compression and uniaxial plane strain extension. An elasto-plastic model with a linear Drucker-Prager type criterion using isotropic hardening and softening and non-associated flow rule was used. A non-local extension was applied in a softening regime to capture realistically shear localization and to obtain a well-posed boundary value problem. A characteristic length was incorporated via a weighting function. Attention was focused on the effect of mesh size, mesh alignment, non-local parameter and imperfections on the thickness and inclination of shear localization. Different methods to calculate plastic strain rates were carefully discussed.

A Study of Localization with Material Properties Using Numerical Method (재료의 특징에 따른 국부화에 대한 수치해석적 연구)

  • 황두순;이병섭;이용성;윤수진;홍성인
    • Transactions of Materials Processing
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    • v.9 no.4
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    • pp.395-403
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    • 2000
  • Formation of Shear Band under the adiabatic condition is widely observed In the engineering materials during rapidly forming process lot a thermally rate-dependent material. The shear band stems from evolution of a narrow region in which an intensive plastic flow occurs. The shear band often plays a role of a precursor of the ductile fracture during a forming process. The objective of this study is to investigate the localization behavior using numerical method. In this work, the implicit finite difference scheme is employed due to the ease of convergence and the numerical stability It is noted that physical and mechanical properties of materials determine how the shear band is formed and then localized. Material properties can be characterized with inertia number dissipation number and diffusion number. It is observed that the dimensionless numbers effect on localization. Using a parametric study, comparison was made between CRS-1018 steel with WHA (tungsten heavy alloy). The deformation behavior of material in this study include an isotropic hardening as well as thermal softening. Moreover, this study suggests that a kinematic hardening constitutive relation be required to predict a more accurate strain level at a shear band.

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Omnipresence of Strain Localization in Soils (흙의 변형국지화 편재에 관한 연구)

  • 권태혁;조계춘
    • Journal of the Korean Geotechnical Society
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    • v.19 no.5
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    • pp.199-210
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    • 2003
  • The development of strain localization within shear zones is frequently observed during soil deformation. In fact, the phenomenon appears to be more often the norm rather than the exception. Conceptually, any soil condition that renders negative work increment is prone to localization. In this study, a broad range of soil and loading conditions are investigated to test this criterion, including: dilative soil subjected to drained shear (standard case), contractive soil sheared under undrained conditions, cavitation in dilative soil in undrained shear, inhomogeneous soils, particle alignment in contractive soils made of platy particles, soils that experience particle crushing, and the shear of low-moisture and/or lightly cemented loose soils. Unique specimens and test procedures are designed to separately test each of these soil conditions in the laboratory According to experimental test results, soil specimens with post-peak strain softening behavior are prone to progressive failure, localization of deformations, and shear banding. The state of stress, the soil density, inherent mechanical and geometrical properties of soil particles, low water content, and heterogeneity can contribute to triggering strain localization. Considering all possible cases of localization, the best method to obtain the critical state line in the laboratory is to use contractive homogeneous specimens subjected to drained shear.

An Investigation on Collapse Behavior of Shear Localization in Elasto- Thermo- Viscoplastic Materials

  • Kim, Hyun-Gyu;Im, Se-Young
    • Journal of Mechanical Science and Technology
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    • v.20 no.12
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    • pp.2178-2188
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    • 2006
  • The stress collapse in the formation of shear bands in elasto-thermo-viscoplatic materials is systematically studied within the framework of one-dimensional formulation via analytical and numerical methods. The elastic energy released in a domain is found to play an important role in the collapse behavior of shear localization. A non-dimensional parameter named the stability indicator is introduced to characterize the collapse behavior, with approximate forms of the incremental governing equations. The stability indicator offers useful information regarding the degree of severity of an abrupt change of deformations during the stress collapse. Numerical experiments are carried out to verify the stability indicator by varying material properties.

LOCALIZATION OF THE VORTICITY DIRECTION CONDITIONS FOR THE 3D SHEAR THICKENING FLUIDS

  • Yang, Jiaqi
    • Bulletin of the Korean Mathematical Society
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    • v.57 no.6
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    • pp.1481-1490
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    • 2020
  • It is obtained that a localization of the vorticity direction coherence conditions for the regularity of the 3D shear thickening fluids to an arbitrarily small space-time cylinder. It implies the regularity of any geometrically constrained weak solution of the system considered independently of the type of the spatial domain or the boundary conditions.

Localization Analysis of Concrete using Bifurcation Theory (분기이론에 의한 콘크리트의 국소화 해석)

  • 송하원;우승민;변근주
    • Proceedings of the Korea Concrete Institute Conference
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    • 1998.04a
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    • pp.353-358
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    • 1998
  • The strain localization is a discontinuous phenomenon that addresses the formation of jumps of the field variables across a singularity surface. It has become widely accepted that the localization may occur as the result of discontinuous bifurcation which corresponds to the loss of ellipticity of the governing differential equations for elasto-plastic continua. In this paper, condition for strain localization in concrete based on bifurcation theory is studied and localization tensor analysis algorithm is employed to determine the directions of localization of deformations in concrete. By applying a plasticity model of concrete into the algorithm, localization analysis is performed concrete under uniaxial tension, pure shear and uniaxial compression.

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A Study of Localization of the Adiabatic Shear Band with Numerical Method (단열전단변형에서 국부화에 대한 수치해석적 연구)

  • 이병섭
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 1999.03b
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    • pp.225-228
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    • 1999
  • In a plastically deformed body the formation of a shear band is widely observed in the engineering materials during rapidly forming process for a thermally rate-sensitive material. The localized shear bond stems from evolution of a narrow region in which intensive plastic flow occurs. The shear band often plays as a precursor of the ductile fracture during a forming process. The objectives of this study are to investigate the localization behaivor by using numerical method thus predict the failure. In this work the implicit finite difference scheme is preformed due to the ease of covergence and the numerical stability. This study is based on an analysised material with hardening as well as thermally softening behavior which includes isotropy strain hardening. Furthermore this paper suggests that an anticipated and suggested a kinematic hardening constitutive equation be requried to predicte a more accurate strain level wherein a shear band occurs.

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