A model for fretting contact of layered materials with interfacial cracks

Surfaces of tightly fitted joints such as splines and dovetails in aero-engines are expected in nominally static contact but experience small amplitude oscillations in practice, leading to fretting fatigue due to nucleation and propagation of micro-cracks. Modern surface coatings are designed to improve the anti-friction/wear capabilities but result in severe stress concentrations across the bonding interfaces due to property mismatch, which may generate interfacial cracks and lead to delamination damage. In this study, a numerical model is developed to investigate the fretting behavior of layered materials with mixed-mode I and II cracks at the layer/layer/sub-strate interfaces in plane-strain conditions. The layer-type impurities are assumed as a bunch of inclusions, whilst the crack-type ones are simulated as discrete edge dislocations. The governing equations are established based on the analysis of stress state, and the impurity-induced displacement is taken into account for an accurate description of the fretting contact. The intensive interactions in the contact system are determined by a multi-loop algorithm, and the calculation efficiency is improved by using the Fast Fourier Transform (FFT) tech-nique. The model can be easily handled without refining meshes near the crack tips, and the calculation time is far less than that of the finite element model to achieve comparable solutions. The model is also capable of simulating cracks with their faces in contact by disabling the loop that determines the mode I crack solution. Details are discussed on the surface traction and subsurface stress influenced by layer films and embedded cracks. The solutions to crack-face displacement are also presented to reveal the potential crack patterns enforced by the time-dependent contact loading. The conclusions are expected to provide insights into enhancing the damage resistance of surfaces suffering from fretting.