Straight cracks are observed in thin coatings under residual tensile stress, resulting into the classical network pattern observed in china crockery, old paintings, or dry mud. Recently, in our lab, we have worked on describe the fracture mechanism where delamination and propagation occur simultaneously, leading to the spontaneous self- replication of an initial template. Surprisingly, this mechanism is active below the standard critical tensile load for channel cracks and selects a robust interaction length scale on the order of 30 times the film thickness. Depending on triggering mechanisms, crescent alleys, spirals, long bands or oscillating paths are generated over a wide range of experimental parameters. We describe with a simple physical model, the selection of the fracture path and provide a configuration diagram displaying the different failure modes. For to know different examples of collaboratives cracks you can see the articles that we have published related with this topic:
J. Marthelot, J. Bico, B. Roman and F. Melo, A new failure mechanism in thin film by collaborative fracture and delamination: Interacting duos of cracks, Journal of the Mechanics and Physics of Solids 84, 214 (2015).