THE EFFECT OF STRESS RATE AND TEMPERATURE ON THE STRENGTH OF BASALT AND GRANITE

Abstract

The ultimate strengths of basalt and granite were measured over a range of stress rates from 2×10 to [Formula: see text] psi per second. A comparison of basalt and granite showed that, although their static strengths were close, their dynamic strengths were different. The static strengths of basalt and granite were 27.5 and 29 kpsi, respectively, at the stress rate of 2×10 psi per second while their strengths at the stress rate of [Formula: see text] psi per second were 59 and 70 kpsi, respectively. In order to obtain an insight into the basic mechanisms of rock fracturing, the combined effects of stress rate and temperature were studied. The strength of basalt was increased from 27.5 kpsi at room temperature to 45 kpsi at liquid nitrogen temperature at the stress rate of 2×10 psi per second. The mechanisms of fracturing were thermally activated. The activation energy for basalt at 50 kpsi equalled 450 calories per mole. The dynamic modulus of basalt measured by the pulse technique was [Formula: see text] psi. The value of the dynamic modulus obtained at a stress rate of [Formula: see text] psi per second was [Formula: see text] psi.