In uniaxial compression tests of rocks, the quasi-static strength has a tendency to increase with increasing strain rate. In order to study this effect of strain rate on strength, a computer model of failure process of rocks was developed with Finite Element Method (F. E. M.) from the view point of stochastic process. In this computer model, inhomogeneity of rock specimens can be easily taken into account by changing elastic constants for each element.
The failure of each element in this model was taken to be the elementary process of macroscopic failure, and the failure process of each element was assumed to be a 3-stage i.e. 2-step Poisson process. By noting that the rate constant of failure for each element is a function of the stress level, the extended concept of stress severity was introduced to express the relation between the stress level and the rate constant of failure.
Although this computer model is based on the most simple assumption, the calculated results represented well the strain rate dependence of rock behavior in uniaxial compression, such as the effect of strain rate on strength and the stress-strain curve. This conclusion was well confirmed experimentally.
