Self-replicating cracks: a collaborative fracture mode in thin films

TL;DR

This paper introduces a novel self-replicating crack mechanism in thin films, where delamination and crack propagation occur simultaneously, leading to complex patterns below the usual critical stress levels.

Contribution

It presents the first observation and modeling of a self-replicating fracture mode involving simultaneous delamination and crack propagation in thin coatings.

Findings

Self-replicating cracks occur below standard critical stress levels.

The mechanism selects a robust interaction length scale about 30 times the film thickness.

Different crack patterns like spirals and bands are generated depending on conditions.

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.