Large deformations of thin plates subjected to impulsive loading

Abstract

The dynamic response of structures subjected to blast and impact loading has been obtained relatively simply using rigid-plastic or rigid-viscoplastic material idealisations. It is essential, however, that the predictions of these idealised theories should be checked against experimental results, and over the past twenty years several experimental studies have been carried out. This thesis describes a series of experiments on fully clamped Circular, square and rectangular steel plates. The final midpoint deflections measured were between 3 and 12 plate thicknesses: and the deflection time history was measured using a light interference technique. While the deflection-time history was being recorded. the impulse was simultaneously being measured by means of a ballistic pendulum upon which the plates were attached. The impulse was provided by sheet explosive which was arranged in such a way that the plate was subjected to a uniformly distributed impulse. In addition an extension of a mode approximation method, based on the assumption that membrane stresses predominate, is presented. This method assumes that the material behaviour can be modelled as rigid-viscoplastic. and that at any instant the shapes of the displacement and the velocity field are the same. Points on the plate surface were first assumed to displace perpendicular to the initial surface: this assumption was then relaxed to permit points to move perpendicular to the current surface. In both cases. the predicted transverse displacements agreed well with the experimental data. The predicted radial strain distribution exhibited trends similar to the experimental data in the case where lateral displacements were modelled.