Stress-relief displacements induced by drilling and three-dimensional modeling of planetary impacts

Citation

Smither, Catherine Louise (1992) Stress-relief displacements induced by drilling and three-dimensional modeling of planetary impacts. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/49fn-dg49. https://resolver.caltech.edu/CaltechTHESIS:09282011-151807180

Abstract

The holographic stressmeter uses double-exposure holographic interferometry to record the displacements induced by the drilling of a sidehole into the borehole wall. The local stresses, which are the result of the far-field stresses, concentrated at the borehole, cause deformation of the surface of the borehole wall near the sidehole. To interpret the data, it is essential to understand this deformation. The initial model used a thin infinite elastic plate subjected to plane stress at infinity. Two-dimensional finite element analysis showed that the displacement depends on the depth of the sidehole. We then developed a new model for the analysis of stress-relief displacements. For holes with a depth/diameter ratio greater than unity, the simple plane stress elastic plate solution breaks down. The revised model, which gives a more exact solution of displacements near the hole, does a better job of fitting the observed data.

A three-dimensional smoothed particle hydrodynamics code was used to model normal and oblique impacts of silicate projectiles on planetary bodies. The energy of the system is partitioned after impact into internal and kinetic energy of the both bodies. These simulations show that, unlike the case of impacts onto a half-space, up to 70% of the initial energy remains in the kinetic energy of the impactor, as parts of it travel past the main planet and escape the system. More oblique impacts retain more kinetic energy in the impactor: 6 to 75% versus 4 to 30% for the normal impacts. Higher velocity collisions also show this trend, as the kinetic energy of the impactor is 2 to 50% of the total for 5 km/s impacts, and 13 to 75% for 20 km/s impacts. Impacts at 20 km/s with an impactor 60% the size of the target completely melted both targets. Three to 4 times more vaporization of the target material occurred on the larger targets. The amount of target material ejected at velocities greater than the escape velocity is found to be higher than that predicted by studies of impact onto a half-space, and slightly less than the amount predicted by theories of catastrophic breakup of asteroids.

Thesis Files