Numerical and experimental analyses on the contact stresses developed during single and successive indentations of coated systems

The mechanical behavior of materials is commonly characterized through the indentation test, during which complex stress and strain fields are developed. In this work, the single and successive spherical indentation of coated systems was studied through experimental and finite element method (FEM) analyses, with emphasis on the causes of the contact stresses at the indentation edge. Considering a system with an AA 6061 substrate and a chromium nitride (CrN) film, a series of single indentations was initially simulated varying the normal load and the diameter of the sphere. These FEM analyses provided values such as the height of indentation pileup and the distribution of radial stresses along the film surface. In both cases, FEM values could be associated with experimental results, by direct measurement of pileup heights and by the amount of circular cracks that propagated during single indentations, respectively. The results indicated that pileup height plays an important role on the stresses responsible for the propagation of indentation circular cracks. However, a direct correlation between the amount of substrate plastic deformation and pileup height was not possible. The numerical and experimental analyses of successive indentations provided further insights on the propagation of circular cracks and its relation with the stress fields and the height of pileups.