Two-dimensional modeling of laser spallation drilling of rocks

High power lasers can weaken, spall, melt and vaporize natural earth materials with thermal spallation being the most energy efficient rock removal mechanism. Laser rock spallation is a very complex phenomenon that depends on many factors. Computer numerical modeling would provides great tool to understand the fundamental of this complex phenomenon, which is crucial to the success of its applications. Complexity of modeling laser rock spallation is due to: 1) rock is a porous media, to which traditional theories of heat transfer and rock mechanics can not be directly applied, 2) the laser rock removal process involves a variety of physical phenomena, and 3) thermolphysical property data for rocks are lacking, particularly the data at elevated temperatures. In this paper, we propose a combined approach to this complex problem, that is establishing models for each of the physical phenomena based on the finite difference method (FDM), then combining them into one numerical procedure using the Constrained interpolation profile-Combined Unified Procedure (C-CUP). The transient temperature and stress distributions in dry or water-saturated rocks exposed to a laser beam are calculated. The spallation boundary and rock removal efficiency are determined. The modeling results provide a better understanding of laser rock spallation and guidelines for selecting processing parameters for fast rock removal.