Size effect during dynamic shear tests with hat-shaped specimens

The failure mechanism and size effect during the quasi-static and dynamic shear tests of hat-shaped specimens were investigated in this study. Three types of specimens with different shear ring thicknesses (800, 400, and 50 μm) were designed. Quasi-static tests were carried out using an electronic universal testing machine, while dynamic impact tests were carried out using split Hopkinson pressure bar (SHPB) tests. The adiabatic temperature rises with different strain rates, and the shear ring thickness was calculated. We found that the adiabatic temperature rises of the specimens with shear ring thicknesses of 800 and 400 μm were much larger than those of the specimens with shear ring thicknesses of 50 μm. The failure surfaces after the SHPB test were investigated via scanning electron microscopy, and the failure surfaces after the SHPB test could be divided into three zones: tensile, shear, and impact zones. The effect of the shear ring thickness and impact speed on the failure surface morphology was discussed. The typical shear stress–strain curves could be divided into three sections: elastic, plastic rise, and plastic plateau sections. Subsequently, a modified Johnson–Cook constitutive model was employed to fit the shear stress–strain results, and the fitted curves showed good agreement with the tested curves.