Interfacial mixed-mode fracture toughness characterization of flexible layered materials

Abstract

Flexible hybrid electronics (FHEs) are finding increasing applications because they overcome many of the limitations of non-deformable traditional electronic boards while still maintaining low-cost fabrication. A critical key to the performance of FHEs depends on the adhesion energy of the interface between printed conductive silver pastes and a flexible substrate. Predicting the fracture energy and evaluating the reliability of these devices under large deformation is crucial in future design efforts. However, because of the size of the components and complex nonlinear behavior of the materials, standard methods of interface characterization may not always be practical. In this study, a new interface characterization experiment for FHE interfaces was created with the help of numerical models. The mixed-mode characterization experiment was performed using a bi-axial loading configuration where the bi-axial loading ratio was used to control the phase angle of the mode mixture. The loading ratio was chosen to produce mode II-dominant loading to better represent typical loading in application. The crack growth was measured using digital image correlation (DIC) by tracking displacement rate changes. Finally, the fracture energy of the interface was calculated based on the experimental data and using finite element (FE) model to include the effects of material inelasticity plasticity in the entire structure.