MODE MIXITY ISSUES IN INTERFACIAL TOUGHNESS MEASUREMENT OF BILAYER SPECIMENS

摘要

The current work focuses on obtaining the interfacial toughness of aluminum-epoxy bimaterial pair and associated mode mixity (the ratio of shear to normal stresses near the crack tip) using bilayer four-point flexure specimen. The analytical and finite element solutions for the interface crack have an oscillatory nature, where stresses and displacements oscillate in the vicinity of the crack tip. Thus, based on such solutions the mode mixity depends on the distance from the crack tip (which is the chosen reference length). In contrast, due to the effects of crack face contact and plasticity, the oscillatory behavior disappears in physical test specimens, eliminating the need for a reference length to specify the mode mixity. In this work, analytical solution based on a fixed material length scale reference length (representing the actual fracture process) is suggested for obtaining the near-tip mode mixity value associated with the interfacial toughness. Alternatively, plasticity can be used in the numerical model to suppress the oscillatory nature.