THE DETERMINATION OF RESIDUAL-STRESSES IN THIN COATINGS BY A SAMPLE THINNING METHOD

Residual stresses in coatings only a few microns thick have been determined by measuring the bending of coated coupons as the substrate thickness is progressively reduced by careful grinding. Samples were magnetically clamped during grinding and the bent profiles were measured by profilometry after release. Great care was taken in the treatment of the data to avoid errors resulting from repositioning the sample. The two in-plane normal components of the residual stress can be found for both coating and substrate. The other components of stress can be shown to be zero by the application of St. Venant's principle and the equation of equilibrium. The method is simple and has several advantages over X-ray techniques. In particular, in those cases where the substrate is still thick compared with the coating, the elastic constants of the coating do not need to be known for the residual stress to be estimated.