Evolutions of the LASer Adhesion Test (LASAT) for the debonding of coatings on substrates above the millimeter range thickness

Abstract
High power laser irradiation on a substrate coated on the opposite side drives a shock whose propagation and consecutive transmission/reflexion at the interface and free surfaces can yield to important traction inside the sample and particularly at the interface. For a given system, traction at the interface can be controlled by laser settings and therefore a LASer Adhesion Test of quality (LASAT) can be realised for many couples of substrate/coating system. The debonding is detected by VISAR measurements at the opposite face to the loading. However, due to the shortness of laser shock at the origin of traction, a strong decay of the initial shock occurs above a few hundredth microns in the substrate. Therefore, debonding cannot be obtained for most samples exceeding the millimeter range thickness.
Several solutions have been investigated for opening up the possibilities of the LASAT process for systems above the millimeter range. One solution would consist in generating the shock on the coating to produce traction at the interface independently of the reverberations of the substrate free surface. An analytical study of shock waves propagation into the coating/substrate system has been performed. It shows that traction can be produced at the interface only when the coating's shock impedance is much lower than that of the substrate. An experiment performed by high power laser shock of an al coating on a thick substrate evidences the debonding.