Experimental and numerical study of stress wave generation and attenuation in copper during laser shock peening

Abstract

A physically based model of laser shock peening is established and experimentally verified. The laser-induced generation of stress wave in the confined geometry is considered directly through the heating and evaporation of the surface layer of copper described by a wide-range equation of state. The structure and attenuation of the stress wave is described by the dislocation plasticity model. In the experimental part, copper plates of three different thicknesses (0.5, 0.8, and 1.0 mm) were irradiated by 11-ns (FWHM) 1064-nm laser with energy densities of 64, 95, 127, and 191 J/cm2, and the back free surface velocity histories were registered by means of photonic Doppler velocimetry. Consideration of different plate thicknesses allows us to decouple the effects of stress wave generation and attenuation and to verify independently the corresponding parts of the model. It is shown that the widely used Fabbro's model tends to underestimate the interface pressure pulse in copper because the stationary plasma expansion assumed in this model is established only after 30–60 ns of laser irradiation with a constant power density. The efficiency value of φ=1 in Fabbro's model is optimal to reproduce the interface pressure pulse at nanosecond irradiation in contrast to the efficiency value of φ=0.5, which is optimal to estimate the stationary level of pressure established for constant power density.