Determination of the effective film mechanical properties in the impact test imprint of coated specimens

If the film of a coated component deforms plastically because of operational loads, residual stresses are developed in the coating material after the load removal. In this way, material mechanical properties changes occur due to endogenous reasons i.e. induced by the coating crystalline structure plastic deformation. In this case, the determination of the effective film mechanical properties has been introduced in a recent publication [1]. Moreover, if the loading conditions lead only to a substrate plastic deformation, the coating remains elastically deformed during the relaxation, due to the substrate residual stresses. Thus, the associated material mechanical properties changes are caused by exogenous parameters related to the permanent substrate deformation. In the present paper, a novel experimental-analytical method based on FEM calculations is introduced to determine the effective film mechanical properties when the coating is stressed elastically due to a plastic substrate deformation. The perpendicular impact test is a convenient experimental procedure to investigate such an effect because under appropriate loading conditions, the substrate deforms plastically and the coating elastically. The pristine constitutive law of the applied PVD film was determined by nanoindentation and FEM supported results evaluation. Impact tests were conducted at various loads and loading cycles. The impact test was simulated by a two dimensional FEM model. Additionally, the developed elastic residual stress fields in the coating and the plastic ones of the substrate in the imprint were determined. In these calculations, a rate-independent anisotropic plasticity with kinematic hardening material law was considered and the film as an anisotropic material with variable mechanical properties in three main directions. Finally, by a FEM supported simulation of the nanoindention, the coating's load-displacement behaviour in various areas of the impact imprint were predicted and the effective coating mechanical properties as well.