Impact or thermal ignition of high explosives, HE, results in deformation that can lead to damage. Fracture or defects, combined with sufficiently high pressure, dramatically increases the available surfacearea and potentially changes even the mode of combustion. Recent impact and cookoff experiments on PBX 9501, (HMX, octahydro-l,3,5,7-tetranitro- l,3,5,7-tetrazocine, with a binder), have shown complex cracking patterns caused by impact or pressurization. Fastreactive waves have been observed to propagate through the cracks at hundreds of meters per second. We present experiments that examine the combustion of mechanically and thermally damaged samples of PBX 9501. Mechanically damaged samples, damaged by quasi-static pressing, exhibit large, -200 microm stress fracture accompanied by extensive rubblization. Combustion experiments determine a 1.4 plus or minus 0.6 MPa critical pressure for the onset of violent convective combustion, consistent with connected porosity of 25 microm. Thermally damaged samples, damaged by heating in a 180 degrees C oven for 30 minutes, exhibit 2-20 microm widely distributed cracking. Combustion experiments indicate a 9.2 plus or minus 0.4 MPa critical pressure for the onset of violent convective combustion, consistent with connected porosity of 4 microm. The burn rate and pressure exponent of thermally damaged PBX 9501 are similar to those of the pristine material.
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