Shear strength and failure modes of double-lap bi-material CFRP/Ni-Cr alloy joint under severe environmental conditions

Abstract

This study was systematically conducted to investigate the dependence of mechanical behaviors of double-lap bi-material joints on various environmental conditions, including room temperature dry (RTD), cold temperature dry (CTD), elevated temperature dry (ETD), elevated temperature wet (ETW), salty spray (SS), and thermal shock cycles (TS) conditions. Compared to the RTD condition, the shear strength of the joint under the CTD and TS conditions shows increases of approximately 50.0% and 9.09%, respectively, but lower values are obtained under ETD (18.18%), ETW (72.73%), and SS (27.27%) conditions. Failure modes of lap-joint are analyzed on fractured surfaces and confirmed by finite element simulation in which the cohesive failure mode mainly occurs with the highest distributed stresses. However, an experimental adhesive failure mode partially appears under the ETD, ETW, and SS conditions. Furthermore, as the less prevalent conditions, the dependencies of the shear strength and failure mode on the exposure time under SS and TS conditions are more thoroughly evaluated based on the scanning electron microscope (SEM) and the energy-dispersive X-ray spectroscopy (EDS) to show microstructures and chemical compositions of the fracture surface, respectively. The effects of environmental conditions, particularly under SS and TS conditions, could provide new insight into designing specific bonded joints.