Simulation Of Shear Band Formation Research Articles

Prediction of low-velocity-impact ignition threshold of energetic materials by shear-band mesoscale simulations

ABSTRACTWhen energetic materials are subjected to a low-velocity impact, they can develop viscoplastic localization, also known as an adiabatic shear band (ASB), leading to unwanted ignition. In this work, the simulation of shear band formation at mesoscale resolution has been incorporated in an ignition model. The simulation results suggest that a low-velocity impact induces the formation of an ASB, leading to ignition. Good agreement was found between the ignition model predictions and available impact test data. The ability of the model to predict the ignition threshold solely on the basis of mesoscale simulations demonstrates its superiority over existing empirical models.

Numerical simulation of shear band formation in elastic material by energy relaxation

AbstractFollowing up the previous work, [1], a new approach to the problem of shear localization is proposed, based on energy minimization principles associated with micro‐structure developments. In this approach, two different material models are included. They represent the behaviour of material at very small strain and very large strain, respectively. Herein, shear bands are treated as the micro‐shearing of rank‐one laminates. The thickness of a shear band represented by its volume fraction is assumed to tend to zero while the strain inside the shear band tends to infinity. The existence of shear bands in the structure leads to an ill‐posed problem which can be solved by means of energy relaxation. The performance of the proposed energy relaxation is demonstrated through numerical simulation of a tension test under plane strain conditions. The presented numerical simulation shows that there is no mesh‐dependence. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Numerical Simulation of Shear Band Formation in Plane Strain Compression Tests on Sand

Numerical Simulation of Shear Band Formation in Plane Strain Compression Tests on Sand

Numerical simulation of shear band formation in hyperelastic material by energy relaxation

AbstractA theorical framework for the analysis of localized failure in hyperealstic material is presented based on the energy minimization principles associated with micro‐structure developments. The theory is predicated upon the assumptions that the thickness of shear band represented by its volume fraction tends to zero as well as that the energy inside shear band is a function of the norm of the deformation gradient. Shear bands are treated as laminates of first order. The existence of shear bands in the structure leads to an ill‐posed problem which can be solved by means of energy relaxation. An application of the proposed formulation to Neo‐Hookean material is presented. Numerical simulation is shown in order to evaluate the performance of the proposed energy relaxation. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Application of a Multilaminate Model to simulation of shear band formation in NATM-tunnelling

A constitutive model formulated within the framework of Multilaminate Models is applied to analyse the practical problem of a tunnel construction according to the principles of the NATM (New Austrian Tunnelling Method). It is demonstrated that the development of plastic shear strains leading to a failure mechanism that involves shear banding can be captured with this model. An enhanced strain softening formulation enables to model both, frictional and cohesive softening behaviour. Due to a simple regularisation technique mesh independent results are obtained with sufficient accuracy for practical purposes.

On the application of a meshless method to shear band problems

Themultiple-scale Reproducing Kernel Particle Method (RKPM), one of the meshless methods, is applied to the analysis of a strain localization problem. The LagrangianRKPM formulation and explicit time integration are employed for the simulation of shear band formation in a viscoplastic material. The mul-tiresolution study is also performed using the multiple-scaleRKPM and then, an efficient high-scale component from the viewpoint of meshless method is proposed for mesh-free adaptive procedures that will be accomplished in the future.

Numerical simulation of shear band formation with a hypoplastic constitutive model : J. Tejchman & W. Wu, Computers & Geotechnics, 18(1), 1996, pp 71–84

Numerical simulation of shear band formation with a hypoplastic constitutive model : J. Tejchman & W. Wu, Computers & Geotechnics, 18(1), 1996, pp 71–84

Numerical simulation of shear band formation with a polar hypoplastic constitutive model

Shear band formation in dry sand during biaxial compression tests is investigated with a polar hypoplastic model. The model is of the rate type and incrementally non-linear. It is established within the framework of a Cosserat continuum. It takes into account Cosserat rotations and couple stresses using the mean grain diameter as a characteristic length. The calculations of biaxial tests with a finite element method are performed for two different meshes and two different mean grain diameters. Initiation of shear bands is triggered by a small inhomogeneity in the initial material properties. From the presence of a characteristic length the calculated thickness of shear zones is almost independent of the spatial discretisation if the size of finite elements is not greater than five characteristic lengths. The numerical results show that the polar effect manifested by the appearance of grain rotations is significant in a shear zone. A quantitative comparison between the numerical calculations and the experimental results shows satisfying agreement.

Numerical simulation of shear band formation with a hypoplastic constitutive model

Recently, a hypoplastic constitutive model based on non-linear tensorial functions was proposed by Wu and Bauer [1] for granular materials. The model covers a broad range of stress level and initial density and is applicable for both initial deformation and fully developed plastic flow. In the present paper, the hypoplastic constitutive model is implemented in a finite element code to investigate the shear band formation in granular materials during biaxial compression tests. Emphasis is placed on the effect of the stress level and of the initial density on shear banding. Initiation of shear bands is triggered by an imperfection in the initial material properties. Comparison between the numerical calculations and the experimental results shows satisfying agreement. The advantages of the hypoplastic approach are outlined.

Simulation of shear band formation in plane strain tension and compression using FEM

A phenomenological constitutive relation using the conventional J 2-flow isotropic hardening yield function as well as a threshold shear stress based yield function that governs a ‘directionally preferred plastic component’ of shear strain, developed by the authors in an earlier work, is used for the simulation of the shear band formation. The constitutive relation which is expressed as an explicit function of elastic constants, deviatoric stress state, direction of the principal shear strain and material flow stresses, is shown to be fully capable of capturing the formation of the shear band even under material hardening conditions and does not demand any prior knowledge of the orientation of the shear band. This dual yield constitutive relation is incorporated in an FEM procedure capable of handling large strains and rotations and a numerical simulation of a tensile and compressive deformation of a plane strain specimen is performed. It is demonstrated that the formation of the shear band can be captured more easily as a natural outcome of the simulation, without resorting to any instability criterion or ‘enriched’ elements that are usually employed in the contemporary procedures. Nevertheless, the usefulness of a ‘local instability criterion’ (Ortiz et al. (1987), Comp. Meth. Appl. Mech. Eng. 61, 189) is demonstrated in this study. The model is verified using the experimental data of Anand and Spitzig (1980, J. Mech. Phys. Solids 28, 113) and the agreement between the results of the simulation and the experimental data is found to be reasonably good.

Plane strain finite element simulation of shear band formation during metal forming

AbstractA plane strain finite element formulation and solution procedure for shear band failure during the plane strain metal forming process are developed and presented. The large strain elastic‐plastic formulation includes a 5‐node 10‐degree‐of‐freedom (d.o.f.) ‘crossed‐triangle’ element, a 4‐node 8‐d.o.f. element with selective reduced integration, an 8‐node 16‐d.o.f. element and a 4‐node 8‐d.o.f. element with an embedded shear band. The formulation includes an elastic‐plastic material model with a modified Gurson yield function and combined isotropic‐kinematic hardening. The solution procedure is based on a Newton–Raphson incremental‐iterative method with an orthogonal projection of zero or negative eigen‐modes when required. Two different examples of plane strain tension test are studied with results compared with available numerical solutions to evaluate the present formulation and solution procedure of the four different elements. The results demonstrate that both types of the 4‐node quadrilaterals are comparable to the 5‐node crossed‐triangle element as well as the 8‐jiode element. To further validate and to demonstrate the predictive capability and practical applicability of the present development, two plane strain metal forming examples are investigated. The first application is a numerical simulation of a sheet‐stretching test with results compared with experimental data for a commercially pure aluminium–magnesium 5182‐O sheet. The load vs. extension history and the through‐thickness strain are compared. The good agreement suggests that it is possible to numerically determine the parameters needed for the modified Gurson yield function. The second application is a numerical simulation of the formation of dead metal zones in the extrusion process. A plane strain extrusion of a short aluminium billet through straight‐sided dies is presented and characteristic features of the formation of dead metal zone are observed.

Numerical simulation of shear band formation in soils

Numerical simulation of shear band formation in soils

Numerical simulation of shear band formation in a frictional-dilational material

The explicit, finite difference code FLAC is used to model shear band development in isotropic, elastic-plastic, Coulomb, non-associated, non-hardening materials. The code reproduces shear band inclinations which depend on both the angle of friction and the angle of dilation. Localization occurs at the yield point. Shear band width is sensitive to the size of the finite difference mesh but is controlled also by the magnitudes of the friction and dilation angles. The distribution of shear bands throughout the specimen is also influenced by the values of friction and, to a lesser extent, of dilation. There is no suggestion that numerical instability or numerical truncation errors are responsible for shear band nucleation.

Numerical simulation of shear band formation in soils

AbstractZones of localized shear strain, called bands, are initiated numerically within idealized cohesive and frictional soil specimens both by inhomogeneities and by imperfect boundaries. Qualitatively the results agree with experimental evidence, and give promise of quantitative analyses using better soil models, when the presence of porewater pressures will be of particular significance.