Cracking Up

[lead: make newsy? or cultural ref? find subhead …]

[background] There's an entire field devoted to the study of cracks and fractures in various materials; for instance, I wrote about fracture dynamics in eggshell-shaped structures for Slate back in 2012. TKTK

[windshield cracking paper from 2013]

"Cracking patterns in thin films appeared in the [scientific] literature 20 years ago, but nobody has assembled such a variety of patterns, and been able to generate them systematically like this," says Harvard University's John Hutchison, who studies wrinkling of thin films that are softer and less rigid than those studied by the French physicists. "Everybody I know in the physical sciences find them fascinating."

[latest research: loosely bonded to the substrate: "Every one of their patterns involves the combination of cracking of the film [with bonding]," Hutchison emphasizes. "This is a crack that goes from the surface of the film straight down to the interface, with a substrate, coupled to the bonding of the substrate, and as the crack propagates this deboning of the interface also occurs. So the curves and such that are associated with thee patterns are due to that combination of film crack and interface crack."

They are able to control the chemistry via two key parameters: the toughness of the interface — how easily or difficult the interface separates — and the toughness of the coating itself, a measure of its brittleness (or lack thereof). By varying those two parameters, along with the thickness of the coatings, Marthelot et al were able to generate a range of crack patterns. Which pattern you get depends on how you tune those parameters.

[give an eg or 2]]

[conclude]

References:

Lazarus, A., Florijn, H.C.B. and Reis, P.M. (2012) “Geometry-Induced Rigidity in Non-Spherical Pressurized Elastic Shells,” Physical Review Letters, 109 144301.

Marthelot, Joel et al. (2014) "Self-Replicating Cracks: A Collaborative Fracture Mode in Thin Films," Physical Review Letters 113, 085502.

McLeish, T.C.B.; Plummer, C.J.G.; Donald, A.M. (1989) "Crazing by disentanglement: Non-diffusive reptation," Polymer 30(9): 1651.

Pons, Antonio, and Karma, Alain. (2010) "Helical crack-front instability in mixed-mode fracture," Nature 464: 85-89.

Vandenberghe, Nicolas; Vermorel, Romain; Villermaux, Emmanuel. (2013) "Star-Shaped Crack Pattern of Broken Windows," Physical Review Letters 110: 174302.

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