Experimental study of laser-driven shock waves in stainless steels

Abstract

Two industrial stainless steels were investigated under laser-shock loading in plasma confined regime with water at nearly 10 GW/cm2 irradiance, driving to stress loadings close to 7 GPa—20 ns at the surface of the targets. A velocimetry interferometer system for any reflector was used to measure shock wave decay and estimate, through the determination of elastic precursors, the dynamic yield strengths at strain rates approaching 106 s−1. Some 50%–100% increases could be found between dynamic yield strengths and static plastic flow limits at 10−3 s−1. Different behaviors were noticed: on AISI 316L Austenitic steel, elastic precursors were shown to have constant values, whatever the propagation depths, whereas on a Martensitic X12CrNiMo12-2-2 steel, precursor attenuations in depth were evidenced. Concerning the application of laser-shock waves to reinforce surfaces, the determination of Hugoniot elastic limits was shown to be useful to predict the plastified depths and the general evolution of plastic deformations in-depth. For instance, comparisons between shock wave profiles and in-depth residual stress fields were shown to give accurate correlations. Lastly, the propagation of laser-shock waves in work-hardened layers was also investigated, which allowed to point out some stress amplitude increases behind 316L foils in the case of a material saturated with defects (shot peening at very high coverage rate).