The influence of inertia and strain-rate on large deformation of plate-structures under impact loading

The static and dynamic behaviour of plate-structures subjected to in-plane axial and compressive impact loading is investigated using the finite element method (FEM). The material model is linear elastic with nonlinear isotropic work hardening characteristics with strain-rate dependence, inertia (via a consistent mass matrix) and geometrical nonlinearities are retained. The FEM results are in very close agreement with those obtained from experiments but the main advantage of the method is that it clarifies the time history behaviour of the model. The previous theoretical work has identified two distinct phases of deformation. Phase one is the compression of the plate, following the inelastic collision, until the structure becomes plastic. This is followed by a second phase of continuous plastic work dissipation in rotation about the hinges formed. The FEM results indicate the nature of the collision strain rate intensity and the differences that exist between static and dynamic modes of deformation response. The numerical modelling also reveals four phases in the deformation process. A phase of stress wave propagation is identified during elastic loading and the build up of high initial axial forces in the specimen. This is followed by a squashing phase, hinge rotation and elastic recovery (or, when the impact energy is high enough, structural closure) before the striker rebounds. The closure phase resembles a severe forming process followed by elastic recovery of the specimen and rebound of the striker. The differences between the various treatments are discussed and analysed in some detail.