Mechanical properties of shock-damaged rocks

Stress-strain tests were performed both on shock-damaged gabbro and limestone. The effective Young's modulus decreases with increasing initial damage parameter value, and an apparent work-softening process occurs prior to failure. To further characterize shock-induced microcracks, the longitudinal elastic wave velocity behavior of shock-damaged gabbro in the direction of compression up to failure was measured using an acoustic transmission technique under uniaxial loading. A dramatic increase of velocity was observed for the static compressive stress range of 0–50 MPa. Above that stress range, the velocity behavior of lightly damaged (D_0<0.1) gabbro is almost equal to unshocked gabbro. The failure strength of heavily damaged (D_0>0.1) gabbro is ∼100−150 MPa, much lower than that of lightly damaged and unshocked gabbros (∼230−260 MPa). Following Nur's theory, the crack shape distribution was analyzed. The shock-induced cracks in gabbro appears to be largely thin penny-shaped cracks with c/a values below 5 × 10^(−4). Moreover, the applicability of Ashby and Sammis's theory relating failure strength and damage parameter of shock-damaged rocks was examined and was found to yield a good estimate of the relation of shock-induced deficit in elastic modulus with the deficit in compressive strength.