Laser Nanosecond Pulse Heating of Surfaces and Thermal Stresses

Laser pulse heating of metallic surfaces finds wide application in industry because of the precision of operation and localized heating of the substrate material. The thermal stresses are developed because of the high temperature gradient generated in the region irradiated by a laser beam. The level of stresses developed becomes important during the laser surface treatment and annealing process. In this study, the laser nanosecond pulse heating of a metallic substrate is considered. Energy transport and thermal stress equations are solved numerically for step input intensity pulses. Because the heating process is axisymmetric, the cylindrical coordinate system is employed. The temperature and stress fields inside the substrate material are computed. It is found that in the early heating period, the temperature rises rapidly in the surface vicinity of the substrate material. As the heating progresses, diffusional energy transport becomes important, in which case the rise of temperature in the surface vicinity attains almost a steady value. The axial stress component is tensile, the radial stress component is compressive, while the tangential stress component is compressive in the region close to the symmetry axis and it becomes tensile as the distance from the symmetry axis increases.