Amit Shaw

Crack Propagation in Bi-Material System via Pseudo-Spring Smoothed Particle Hydrodynamics

A Smoothed Particles Hydrodynamics (SPH) based framework with material constitutive model is developed to simulate crack initiation and propagation in a bi-material system. An efficient immediate neighbor interaction is formulated by connecting neighbors through pseudo-springs. A damage evolution law defines degradation of the inter-neighbor spring forces and corresponding reduced interaction is introduced in mass, momentum, and energy-conserving particle collocation. The proposed technique is validated through a simple test on a pre-notched bi-material system producing a conformal crack path.

Improved Procedures for Static and Dynamic Analyses of Wrinkled Membranes

An analysis of large deformations of flexible membrane structures within the tension field theory is considered. A modification-of the finite element procedure by Roddeman et al. (Roddeman, D. G., Drukker J., Oomens, C. W J., Janssen, J. D., 1987, ASME J. Appl. Mech. 54, pp. 884-892) is proposed to study the wrinkling behavior of a membrane element. The state of stress in the element is determined through a modified deformation gradient corresponding to a fictive nonwrinkled surface. The new model uses a continuously modified deformation gradient to capture the location orientation of wrinkles more precisely. It is argued that the fictive nonwrinkled surface may be looked upon as an everywhere-taut surface in the limit as the minor (tensile) principal stresses over the wrinkled portions go to zero. Accordingly, the modified deformation gradient is thought of as the limit of a sequence of everywhere-differentiable tensors. Under dynamic excitations, the governing equations are weakly projected to arrive at a system of nonlinear ordinary differential equations that is solved using different integration schemes. It is concluded that, implicit integrators work much better than explicit ones in the present context.

An axisymmetric model for Taylor impact test and estimation of metal plasticity

The impact of a flat-ended cylindrical rod onto a rigid stationary anvil, often known as the Taylor impact test, is studied. An axisymmetric model is developed to capture the deformation behaviour of the rod after impact. The most distinctive feature of the proposed model is that it takes into account the spatial and temporal variation of both longitudinal and radial deformation and consequently the strains and strain rates. The final deformed shapes and time histories of different field variables, as obtained from the model, are found to be in good agreement with corresponding experimental and numerical results reported in the literature. The proposed model is then used to formulate an inverse framework to estimate the Johnson–Cook constitutive parameters. In the inverse formulation, the objective function is constructed using the final deformed length and diameter at the impact end of the retrieved rod. Finally, the potential of the proposed model in estimating material parameters is illustrated through some examples.

A generalized model for dynamic deformation and failure of clamped beam under impact loading

A mathematical model representing the dynamic behaviour (both plastic deformation and fracture) of a clamped beam under impact loading is developed. Indentation at the impact point, transverse deformation, formation and propagation of plastic hinge, arrest of plastic hinge leading to plastic work concentration and finally failure are the physical processes which constitute the basis of the derived model. The effect of imperfection is also incorporated. Imperfection is considered in the form of a π-shaped notch located at the impact point, at supports or at both. The distinct feature of the present formulation is that it accommodates different possible deformation and failure modes in a single model. Final plastic deformation, time histories of different field variables and failure modes as predicted from the derived model are found to be in good agreement with the corresponding experimental and numerical results. This model provides a quick understanding of the dynamic behaviour of beam under impact and also the effect of various underlying parameters which may be useful for forming design provisions for impact-resistant structures.