Thermal stress development due to laser step input pulse heating

The closed form solution for the thermal stress distribution inside the substrate material is obtained for a stress-free boundary condition at the surface, which is the most practical situation in laser material processing. Since the molecules in the liquid and gas phases are free to move, the thermal strains in these phases are significantly small, so that the thermal stress field is formulated for the solid phase and the heat conduction equation for solid heating, therefore, considered only. It is found that the temperature in the region next to the surface vicinity drops sharply while the temperature reduces gradually in the surface vicinity due to the high amount of energy absorption from the irradiated field in this region. The variation in the temperature gradient in the surface region results in thermal stress waves propagating into the substrate material at a constant speed. Thermal stress below the surface is compressive due to high thermal strain developing in this region.