Sliding mode of multiple cracking of thin coatings

Under tension of flat specimens with slightly deformable coatings two types of multiple cracking can occur: front-wise development of opening-mode cracks as well as formation of a system of sliding-mode cracks oriented along the conjugate directions of maximum tangential stresses (τ_max). Their effect on the mechanical behavior of coated materials can be substantially different. Opening-mode cracks decrease material ductility; at larger coating thickness they reduce specimen strength and, what is most important, fatigue lifetime. When a system of conjugate sliding-mode cracks is formed, ductility, strength and fatigue durability remain at the same level or even increase. In the given brief review we formulate the conditions for multiple cracking initiation and development.