Load-rate dependence of rock tensile strength testing: Experimental evidence and implications of kinetic fracture theory

This paper presents experiments showing that the nominal tensile strength of granite specimens measured in three-point bending tests increases with the logarithm of the loading rate. Based on these experiments, we propose a criterion for macroscopic breakage wherein failure occurs when a given proportion of available atomic-scale bonds are broken. Consistent with the experiments, this theory predicts that a linearly increasing applied load is expected to result in a linear relationship between the load at the time of macroscopic breakage and the logarithm of the loading rate. Furthermore, the parameters ascertained from the results of the increased load experiments give a lower bound prediction with the same slope for the time to failure under constant loading.