Thermal-mechanical Effect During Ms Pulsed Laser Heating Brittle Material

In this paper, the temperature field and thermal stress field during ms pulsed laser heating, scanning brittle materials are investigated by numerical analysis and experiment research. The ms pulsed laser induced damage of brittle materials and the damage mechanisms, controlled fracture during scanning process, the evolution of plastic zone during the laser heating are studied by analyzing the development of the thermal stress field.Based on heat transfer theory, an axisymmetric mathematical model is established by using finite element method (FEM) to compute the temperature field and thermal stress field during ms pulsed laser static irradiating brittle materials. The simulation results of the thermal stress show that the fracture will be induced around the laser heating zone. The laser-induced damage behavior of single-crystalline silicon is investigated with a Nd:YAG laser (1064nm) at different laser fluences under ms pulsed mode, damage morphology is also studied in detail. From the thermal stress simulation analysis, explanation about the crack distribution is given.A three-dimensional finite element thermoelastic calculational model is established to simulate the pulsed laser scanning process. The development of the temperature field and thermal stress field were investigated during the pulse duration and changes of stress intensity factor around crack tip were analyzed. The simulation results show that:there are two tensile stress zone induced by the laser heating zone, and when the laser spot near the edge of the silicon wafer, the larger tensile stress is induced at the edge of the silicon wafer, during the pulsed laser scanning process, the pre-existing crack can induce the fracture propagate along the along the moving direction of the laser beam. The process about two-point pulsed Nd:YAG laser scanning silicon wafer is also investigated. Meanwhile the effects of laser power and the distance between the two laser spots on the development of stress intensity factor around crack tip.The evolution of plastic zone in the brittle material is investigated by using thermal elasto-plastic constitutive relation and incremental FEM. The influence of the combined action of thermal stress expansion and thermal softing on thermal stress is analyzed.These research results of this paper can offer the theoretical and experimental foundation for ms pulsed laser induced damage, laser cutting, laser forming.