Abstract

The deformation of a moderately thick plate after it is exposed to a single-mode laser pulse is investigated with the single pulse deformation (SPD) model. The problem is known in many laser processing applications such as welding, cutting and metal forming, where pulsed techniques are used and the sample is usually flat. In metals the light is absorbed only at the thin surface layer, which is heated up more than the rest of the plate¹. Consequently, thermal expansion decreases along the plate thickness². In the cooling phase the deformation sinks back into the plate. When during the heating phase the internal Von Mises equivalent stress exceeds the yield stress, the material around the plate center becomes plastic. Therefore, the pressure exerted onto its elastic surroundings drops and the initial outward expansion of the plastic area is less than would be expected. Instead of expanding this region grows thicker. In the cooling phase the plastic matter returns into the elastic state almost immediatelyand there is no time to reshape into its primary form. The upper layers stays shorter and thicker, and hence the plate's center bends away from the top surface.

© 1998 IEEE