Some detailed stress-strain curves for rock

Detailed axial stress-strain curves for the compression of free and confined cylindrical specimens of an Australian sandstone and a South African quartzite are presented. These show that the secant moduli of minor stress cycles, within a major stress cycle, are significantly greater than either the secant or tangent modulus of the major cycle. The specific energy loss of the minor cycles is less than that of the major cycle. The observations are discussed in terms of the behavior of Griffith cracks, and the effect of the observed phenomena on the propagation of stress pulses is considered.