Impact Test Applications Supported by Fea-Models in Surface Engineering for Coatings Characterization

The impact test is used since several years, among others, for characterizing the fatigue strength, creep, adhesion and residual stresses of coatings at ambient and elevated temperatures under dry or lubricated conditions. In recent time, the impact test has also been applied to determine stress, strain, strain rate data of coatings and their substrates. A main advantage of this test method is that in many cases, it can be employed directly on the coated parts and not on specimens. The obtained experimental results are evaluated by convenient FEM supported algorithms. Based on these algorithms, critical data for predicting the life span of coated parts such cutting tools, bearing etc. and for planning appropriate replacements can be determined. The paper renders an overview about the development of impact test devices, experimental techniques and results evaluation methods. Characteristic examples highlighting the quantification of the fatigue strength of PVD coatings and its adhesion via a critical equivalent and shear stress respectively as well as of the temperature-dependent interfacial fatigue strength of diamond coatings via a critical shear stress are shown. The residual stresses in the diamond film structure play a dominant role on the interfacial fatigue stress and are calculated by appropriate FEM-evaluation of the inclined impact imprints.