Physical and numerical evaluation of effect of specimen size on dynamic tensile strength of rock

Abstract

It is well known that both the specimen size and the loading rate can affect the tensile strength of rock specimens. In this study, the combined effect of loading rate and specimen size on tensile strength was investigated by performing some physical and numerical Brazilian tests on specimens with notch and without notch. The dynamic tests were performed using the Split Hopkinson Pressure Bar apparatus. A type of dental gypsum commercially known as Snow Rock was used to prepare the molded gypsum specimens for the physical tests. The CA3 computer program was utilized for the numerical simulation. The bonded particle model for simulation of the rock together with the implemented micromechanical model was able to capture many features of the physical test results. It was shown that the notched specimens were much more sensitive to the loading rate. Furthermore, the results suggested that there is a critical stress rate at which the specimen size has no effect on the specimen strength. For loading rates greater than the critical one, with the increase in the specimen size, greater tensile strength was obtained. Fracture mechanics size effect was partially observed for the applied loading rates smaller than the critical rate.