DEBOND FRACTURE AND KINKING IN MULTILAYER SYSTEMS: THEORETICAL SOLUTIONS AND PRACTICAL APPLICATIONS
Debond fracture is a dominant failure mechanism in multilayer systems used for various current applications, from laminated and sandwich structural components to protective coatings and thermal barrier coatings; from microelectronic devices, in the electronics and flexible electronics fields, to biomedical devices. Debond cracks originate and propagate at the interfaces between the layers, which often have disparate mechanical and thermal properties; they may kink out of the interfaces and lead to unexpected collapses, such as those observed in marine sandwich composites where these mechanisms may yield to the detachment of entire portions of the core from the outer facesheets. The presentation reviews elasticity techniques and closed form solutions recently derived by the authors for the fracture parameters of interface cracks in edge cracked orthotropic layers, bimaterial layers and sandwich beams and for the crack tip compliance coefficients (root rotations and displacements) in bimaterial isotropic and orthotropic layers. Practical applications of the solutions will be discussed: operative formulae for the characterization of the interfacial toughness in classical and novel fracture mechanics specimens; calibration of the parameters of one-dimensional model; and analytical criteria for kinking in multilayer systems.