Tensile Strength Test of Rock at High Strain Rate Using Digital Image Correlation

Tensile strength test of rock at high strain rate was experimentally performed by utilizing the nature of the strength difference. A magnitude of the tensile strength of brittle materials such as rock is much smaller than that of compressive strength. A compressive wave was produced by dynamic loading of explosive charge and made incident on a one end of a rock specimen bar. The compressive wave traveled through the specimen bar and it reflected at the free surface of the opposite end as a tensile wave with reversal amplitude. The tensile wave will cause the spall failure of the specimen at a specific distance from the free surface where the superposition of tensile and compressive waves exceeds the tensile failure strength of the specimen, usually referred to as Hopkinson effect, The dynamic behavior was observed at the side face of the bar specimen using a high-speed video camera, and the captured images were used to analyze the surface displacement behavior using a digital image correlation (DIC) technique. Strain and strain rate distributions on the specimen bar during impact loading were evaluated. The relationship between strain rate and dynamic tensile strength was discussed.