Heterogeneity in deformation of granite under dynamic combined compression/shear loading

By adding two blocks with symmetrical oblique surfaces, the dynamic behaviors of granite under combined compression/shear loading are investigated by the modified split Hopkins on pressure bar device (SHPB). High speed camera is employed for image acquisition of the specimens with manual speckle patterns. The transverse tensile strain field and maximum shear strain field are calculated and presented by the Digital image correlation (DIC) method. Evolution of number density of strain amplitude is found to obey the bimodal (two-peak) Weibull distribution. The first peak (peak 1) and second peak (peak 2) are dominated respectively by the evolution of local deformations in the matrix part and failure part of specimen. Amplitude of Peak 2 can also illustrate the distribution extent of activated microcracks under external loads, and is not obvious in quasi-static tests. A governing equation is proposed to describe the statistical evolution of strain fields. The evolution rate of quasi-elastic strain, the damage nucleation rate, and the contribution of heterogeneous deformation of the failure part to whole deformation in specimens are derived accordingly. The results show that the heterogeneity is loading-rate dependent and/or shear-component dependent.