Response of dry- and liquid-filled porous rocks to static and dynamic loading by variously-shaped projectiles: Fid-Bau Portal

Response of dry- and liquid-filled porous rocks to static and dynamic loading by variously-shaped projectiles

Rogers, C. O. / Pang, S. -S. / Kumano, A. / Goldsmith, W.

Summary The present investigation was undertaken to study the response of both dry and liquid-filled porous rocks to static and dynamic loading of penetrators with various tip shapes. Eighteen static and forty-eight dynamic tests were conducted involving 6.35 mm diameter indenters featuring flat, hemispherical and 60° conical tip shapes on three different rocks in the energy range from 1.57 to 5.63 J. Force-penetration data were collected by means of strain gages attached to the penetrators. For all three materials, the magnitude of the resistive forces for a given input energy decreased in the following order: (i) dynamic penetration into a dry sample, (ii) dynamic penetration into a fluid-filled specimen, (iii) static loading of the fluid-filled rock, and (iv) static, loading of the dry rock. An unusual observation for the dynamic force-penetration curves was the temporal disparity between the peak force and maximum deformation, which must be attributed to inertial factors. Based on the experimental data, an analytical rigid-body model was constructed that contained both a static and a dynamic component of the resistive force with the objective of quantifying the effect of dynamic loading and the presence of fluid on the response of the rocks. The dynamic component was portrayed as a viscous resistance proportional to the velocity of the penetrator and the contact surface area which is a function of the indentation. It was found that the model provides a good predictive capability for the dynamic force-indentation relations for prescribed materials and tip geometries upon use of but a single constant for the viscosity.