ADHESION AND ELASTIC CONTACT STRESSES OF COATING SUBSTRATE SYSTEMS UNDER NORMAL AND TANGENTIAL LOADS/

Elastic indentation tests (spherical indentor) of coated substrates wh ich had different interface structures (abrupt to gradual transition) were analyzed by theoretical and experimental methods. For the theoret ical investigations, models with several sublayers which had different elastic parameters were applied. Analytical solutions of the deformat ion and stresses in both the substrate and the coatings were found. Re sults are presented for several combinations of the mechanical propert ies of the substrate and film. Special attention was paid to the shear ing stresses in the interface and the tensile stress on the contact ed ge. These stresses may cause crack formation and film delamination. Fr om a combined theoretical and experimental investigation, the critical stresses was derived, this being a measure for the adhesion and tough ness of the coating. In addition, we calculated the von Mises criterio n for plastic deformation of the composite and compared this with the pressure necessary for the generation of Hertzian and interface cracks . To consider adhesional problems of coating/substrate composites, we also investigated indentations with a load component in a tangential d irection. In this way, we obtained stress distributions very similar t o those found in a scratch test but without dynamics.