Stress Wave Passage in Selected Rock Fabrics

Abstract

P'AVWEPSABSTRACT. This study is on the transmission and decay of pulses produced by impact in a very coarse-grained leucogranite, a fine-grained spessartite, and a fine-grained to aphanitic basalt. For most tests, ballistically suspended Hopkinson bars of these rock materials, 0.845 inches in diameter and 18 inches long, were subjected to longitudinal impact by i-inch-diameter hardened steel spheres at an initial velocity of 3,250 + 1.5% ips. Strain gages attached to the specimens at variLtas stations recorded the shape and velocity of propagation of the resultant wave in the rock rod. Similar experiments were performed on an aluminum alloy rod of identical size to assess the magnitude of the dispersion resulting from the three-dimensional character of the rod. The nature of the pulse transformation during passage permits an assessment of the validity of various models proposed for geologic substances in the field of seismology. Static tests on virgin and shocked rods were generally found to agree with predicted effects of stress wave passage on the rock structure.These effects include compressive-strength loss in the impact end and tensile-strength loss in the distal end as the result of oriented fractures and a general lowering of the static Young's modulus.Although these studies were conducted on rock, the general concepts developed are fully applicable to an understanding of the dynamic behavior of artificial granular brittle solids, such as explosives and concrete.