Influence of stress state on dynamic breakage of quartz glass spheres subjected to lower velocity impacting

Abstract

The breakage process of glass spheres under impact loading is very complex due to the transition of two failure mechanisms, i.e. tensile failure and shear failure, with the increase of loading rate. In order to investigate the influences of stress state adjustment on sphere breakage, three kinds of transmission bars, i.e. steel bar, aluminum bar, PMMA bar, and double-sphere specimens are employed by the modified conventional Split Hopkinson Pressure Bar (SHPB) device. These experiments are conducted under lower impact velocity, which evaluated by the critical state of single sphere failure. Larger critical strain and lower critical strain rate for sphere breakage are obtained when replacing the steel transmission bar with the PMMA bar. The failure properties of inner geometric structures by adjusting failure sequences of the double-sphere specimens. Based on the evolution of particle size distributions and local deformation distribution by the Digital Image Correlation (DIC) method, two-stage failure model is obtained. The first stage of sphere breakage results from the diffusion of local Hertz cracks at the contact areas, which mainly caused by local shear failures, and the second stage results mainly from the penetrated oblique cracks along impact direction, which mainly caused by transversal tensile failures. Adjustment of stress and strain fields by these two schemes reveals these intrinsic influences on sphere breakage, and failure law, involving the effects of local strain, local strain gradients, and local strain rates, is preliminarily discussed. Further theoretical analyses are conducted to investigate the movement of the diffusion fronts. It is of significant reference for understanding the dynamic failure mechanism of brittle granular matter.