Laser thermoelastic generation in metals above melt threshold

Abstract

We have established the detailed spatio-temporal evolution of heat conduction of the irradiated sample due to the incidence of a laser pulse, including the temperature rise of the solid phase preceding the melting, and the appearance, subsequent growth and then contraction and disappearance of the melt pool due to re-solidification. With these we have identified three regimes of stress evolution: (1) presence of lateral compressive stress in solid that has undergone mild heating without melting, (2) absence of lateral stress in the molten metal, (3) presence of lateral tensile stress in re-solidified and cooling solid. The gradient of the lateral stress, integrated over depth, represents the evolving radial force distribution, which can be regarded as acting at the surface. From the radial surface, stress distributions the radial and normal surface forces were computed. Then we convolved surface force distributions with plate’s Green’sfunctions. We have also performed FEM calculations of the epicentral displacement response to surface forces and find very good agreement with Green’s functions calculations.