Three-dimensional finite element modeling of subsurface median crack in trilayer sandwiches due to contact loading

A type of crack system, subsurface median cracks, observed in spherical contacts of brittle coating-bond-substrate sandwich structures, is investigated using finite element method. This crack system emanates from the low surface of the brittle layer and extends transversely towards the top contact surface, resulting in ultimate failures of the structures. In a step-by-step simulation, the crack front is constructed based on a set of points along the front using a cubic spline approximation; therefore, complex crack shape can be represented with sufficient accuracy. A simple power law of fatigue crack growth is invoked at each step to determine the relative increments of these points. Followed by the descriptions of some technical details, this numerical method is implemented through modeling a typical sandwich structure with various modeling parameters, and simulation results are confirmed with experimental observations qualitatively.