Stiffness of Contacts Between Rough Surfaces

The effect of self-affine roughness on solid contact is examined with molecular dynamics and continuum calculations. The contact area and normal and lateral stiffnesses rise linearly with the applied load, and the load rises exponentially with decreasing separation between surfaces. Results for a wide range of roughnesses, system sizes and Poisson ratios can be collapsed using Persson's contact theory for continuous elastic media. The atomic scale response at the interface between solids has little affect on the area or normal stiffness, but can greatly reduce the lateral stiffness. The scaling of this effect with system size and roughness is discussed.Comment: 4 pages, 3 figure

HT2003-40298 A 3-D NUMERICAL MODEL FOR ABLATION PHENOMENA AND THERMAL STRESS EVOLUTION DURING LASER MACHINING

ABSTRACT A full 3-D transient model is developed for the ablation phenomena and thermal stress evolution during laser cutting and/or drilling of ceramic plates. The computational methodology is based on the Galerkin finite element method along with the use of a fixed grid algorithm to treat the thermal ablation resulting from an applied laser source. The present model is able to model any complex ablation operations involving discontinuity in geometries, as encountered in laser cutting and laser drilling operations. This is an advantage over the front tracking method by which the ablation moving interface is precisely tracked in time and which is useful for simple geometries. The laser ablation model is coupled with a thermal stress model to predict the evolution of thermal stresses, which arise due to a rapid change in thermal gradient near the laser beams. Model predictions compare well with the available data in literature for a simple configuration. Results obtained from model for both dual pulsed laser cutting and single laser drilling are discussed. INTRODUCTION Lasers have now been widely used as a manufacturing tool for high precision cutting and drilling operations Such an advantage is of critical importance when it comes to cut the materials inherently brittle such as alumina-based thin ceramic plates. To take a full advantage of these unique near-zero force features, laser machining operations must be designed such that localized laser heating does note generate an infernal spot