Self-Replicating Cracks: A Collaborative Fracture Mode in Thin Films

Abstract

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. Here, we present a novel 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 or long bands 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.

Tearing of thin sheets: Cracks interacting through an elastic ridge

“…[37] and subsequently used, for example, in Refs. [13,26,27]. It is briefly recalled here for self-containedness.…”

“…They are observed during the desiccation of films made of colloidal suspensions, like bentonite clay or cornstarch [5][6][7][8][9][10][11], in sol-gel films [12,13], in broken objects like windows [14][15][16], or in sea ice [17,18] and ice floes collisions [19,20].…”

Evaporation‐Directed Crack‐Patterning of Metal–Organic Framework Colloidal Films and Their Application as Photonic Sensors

“…Recently, crack-patterning has emerged as an alternative and convenient « bottom-up » method to pattern thin films. [4] In controlled conditions, crack propagation can proceed following straight, oscillatory or spiral-like paths [5] and/or it can be guided by micronotches (made by lithographic techniques) toward complex patterns and devices. [6] Alternatively, as observed in mud's cracks, Allain and Limat [7] demonstrated that controlled drying of colloidal droplets resulted in the formation of parallel periodic cracks oriented by the evaporation front-line.…”

A new failure mechanism in thin film by collaborative fracture and delamination: Interacting duos of cracks

“…Although a large variety of patterns can be observed for different triggering conditions [24], we focus in this paper on the paradigm case of duos of cracks In this particular example, the cracks initially linked by a narrow delamination front, start to diverge but quickly converge towards a steady width W 2 . The pictures are taken with a constant time lap of 2 s. (b) Opposite case where the initial width is larger than W 2 , leading to the same optimal width.…”

“…Several failure modes compete in the sector of the diagram where e > Γ 0 i and e > Γ 0 c /2γ. Complex fracture patterns such as spiral and oscillatory paths resulting from "follower cracks" can indeed be observed [24] in addition to the the fracture and adhesion energy, and γ a numerical prefactor that depends on the mismatch of material properties between the substrate and the coating. The x-axis corresponds to the comparison of the residual energy density to the interfacial energy, whereas the y-axis compares residual elasticity to the material toughness.…”