Measurement-based evaluation of interfacial polymer layer inserted in sound deadening laminated sheet

Mixed mode bending (MMB) test associated with measurement of crack tip opening displacement (CTOD) is a practical method to experimentally evaluate mixed-mode cohesive zone model (CZM) properties of polymer layers in various mixed-mode ratios. However, it has an obvious limitation that does not allow for plastic bending of adherends during the tests, making it difficult to evaluate the polymer layer inserted in the sound deadening laminated sheet (SDLS) comprising thin metal sheets which are vulnerable to the plastic bending. This paper provides an experimental technique to suppress the plastic bending of the thin metal sheets during the MMB test. Supporting tools were designed, and bonded to the both outer surfaces of the SDLS. Until delamination occurred, the evolution of fracture toughness (G) was evaluated, and the CTOD was measured in the stereo image using a digital image correlation system. Finally, the mixed-mode CZM properties was successfully established based on the differentiation of the relation between the evolution of G and CTOD.