Finite element analysis of shear band failure with particular reference to circular plate impact
This thesis addresses the problem of the numerical simulation of the shear band or 'plugging' mode of failure in metallic solids. Particular reference is made to the normal impact between blunt projectiles and circular plates of thin to intermediate thickness. The thesis presents a two dimensional axisymmetric and plane strain finite element computer program related to the Lagrangian reference frame. A four node element with one point quadrature and associated stabilisation is utilised, and is shown to be superior to standard isoparametric implementations when applied within an explicit time integration scheme. Finite deformation capabilities are included, together with material nonlinearity in the form of a von Mises elastic-plastic model. The algorithms used in this work are dictated to a large degree by the emphasis which is placed upon efficiency, although this is not at the expense of accuracy. Numerical stability in the presence of severe stress gradients is achieved through the use of an artificial viscosity scheme. The impact conditions along the contacting interface are governed by the use of a penalty-based slideline technique which permits arbitrarily large relative deformations of the contact surfaces. With the foregoing numerical basis, the penalty-based slideline technique has been extended in this work to facilitate the discrete modelling of the fracture process present during plugging. The computational model has been embedded within the LUSAS finite element system which provides extensive pre and post processing facilities. A detailed discussion of the problems involved in the solution of high velocity impact calculations is given, together with an assessment of the effects of several material related parameters on the solution. several numerical comparisons with experimental evidence are also performed to indicate the effectiveness of the method. Finally, relevant conclusions have been made and suggestions for further study are provided.