Measurement of interface strength by the modified laser spallation technique. I. Experiment and simulation of the spallation process

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Abstract
Part I of this paper presents the modified laser spallation technique for measuring the tensile strength of planar interfaces, using a Doppler displacement interferometer. In this technique, a laser‐produced compressive stress pulse in the substrate, reflecting from the coating’s free surface pulls the interface in tension and leads to its failure if the tensile amplitude is high enough. The current technique is an improvement over the previous one, since the interface stress is determined directly by recording the coating or substrate free‐surface velocities using a laser displacement interferometer. The recorded surface velocity is related to the interface stress via an elastic wave equation simulation. The process of coating spallation is investigated, and the effect of the stress pulse profile and the coating and substrate characteristics on the interface tensile stress is studied using the simulation. Several interface stress charts are given for wider applicability of the modified technique.

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