Mechanoluminescent study for optimization of joint design on cross tension test

To develop cross tension (CT) tests for adhesive dissimilar material joints, we investigated the design of CT test specimens (particularly the shape of the bonding area) through mechanoluminescence. To clarify the factors that cause high scattering of cross tension strength (CTS) values in the case of conventional CT specimens with square adhesive regions, we visualized the mechanical behavior during the CT test (particularly the fracture progress behavior inside the adhesive layer) by using mechanoluminescence. The mechanoluminescence revealed inconsistent patterns in each CT specimen with a square bonding area. This indicates that the different stress concentration behaviors and crack growth/peeling behavior during the CT test are factors that cause high scattering of CTS values. Meanwhile, in the case of CT specimens with circular adhesive regions, the scattering of CTS values was reduced significantly, and the mechanoluminescent patterns were consistent as circles of almost identical size in all the specimens. It can be considered that mechanoluminescence has the potential to effectively visualize mechanical behavior for optimizing test designs.