SUMMARY

Dissimilar material systems are often prone to interfacial delamination. Delamination failure can occur in different modes of loading. The interfacial fracture strength of the bonding materials is a function of the mode mixity. Therefore, it is essential to characterize the interfaces of dissimilar materials for multiple loading modes to develop a holistic understanding of the interface behavior. It is critical to design and develop reliable experimental and numerical test techniques to effectively characterize the interfaces of dissimilar materials. Here, two novel test methods have been designed to effectively characterize the interfaces in mode I and combined mode I-III loading. An innovative test method called Crowbar Loading(CBL) is developed to characterize copper/epoxy mold compound interface in near-mode I conditions. In the proposed test, a cylindrical roller is sandwiched in the delaminating interface, and the roller acts as a fulcrum to facilitate crack propagation. Although the externally applied load is compressive on one side of the fulcrum, the fulcrum translates the applied external load into an opening-mode load at the crack tip. The proposed test does not use any fixtures and provides results at a mode mixity that is not achieved by other conventional test methods, such as double cantilever beam (DCB) testing. In addition to the CBL test method, a modified axial-transverse cantilever beam(ATCB) test is developed to facilitate testing the interfaces under mode I -III combination loading. The ATCB test has angular off-set test fixtures to accommodate for the application of out-of-plane shear loading in addition to normal loading at the crack front of the interface. In conjunction with the experiments, numerical and analytical methods are also developed to extract the critical fracture parameters, like critical strain energy release rate and mode mixity, to help characterize the interfacial behavior in different loading modes.