Snap-through Crack Propagation in Architected Bonded Interfaces Analyzed Using a Mechanoluminescent SAO/E Coating

We investigate the mechanics of crack propagation inarchitectedadhesive joints whose adherends are inspired to the base plate ofthe barnacle Amphibalanus (=Balanus) amphitrite, and feature an array of buried hollowcylindrical channels located perpendicularly to the direction of crackgrowth. Selective laser sintering is used to obtain the adherendsthat are subsequently bonded in the double cantilever beam configurationto ascertain the mechanics of crack growth. Finite element (FE) simulationsare deployed to determine the strain energy release rate (ERR) andto elucidate the salient features of the fracture process. It is shownthat the channels induce a modulation of the ERR and enable a cracktip shielding mechanism. Besides, FE simulations based on a cohesivezone approach indicate the occurrence of crack pinning/depinning cyclesthat are validated via experiments. A highlight of the present studyis the use of a mechanoluminescent (ML) coating to unravel the evolutionof the transient stress field in the crack tip region. The coatingcomprises an optical epoxy resin loaded with doped strontium aluminatephosphors (SrAl2O4/Eu2+) and convertsmechanical energy into light emission with intensity proportionalto the magnitude of mechanical stress. By combining the ML emissionpatterns with the stress distribution obtained from FEA, we unveilinteresting details of snap-through cracking in architected bio-inspiredadhesive joints.