On fracture characteristics of adhesive joints with dissimilar materials – An experimental study using digital image correlation (DIC) technique

Abstract With expanding use of multi-materials in vehicle components for attaining light-weighting structures, growing interests have been refilled in the adhesive bonding technique attributable to its compelling advantages to bond dissimilar materials, especially for carbon fiber reinforced plastic (CFRP) composite and metals. A significant issue related to the bonding of dissimilar materials is, nevertheless, that there are substantial differences between adherend material properties, which often lead to different structural and fracture responses. This study aimed to investigate the effects of adherend thickness and adherend material types (e.g. steel, aluminum, CFRP composite) on the fracture behavior of the joints. The adherend deformation and fracture processes of the joints were monitored by the charge couple device (CCD) cameras during the tensile tests. A digital image correlation (DIC) technique was used to capture full-field, out-of-plane deformation of the adherend, the strain distribution and strain evolution along the bondline so that the fracture process can be characterized visually. The microscopic and macroscopic studies on the fracture surface were also carried out to explore the influences of adherend thickness and material types on the failure modes of the joints quantitatively. The results divulged that the joint strength increased with increasing adherend thickness; and the sensitivity of adherend thickness on the joint strength depended on the joint material types. When the adherends underwent the elastic deformation, adherend stiffness affected the joint stiffness and joint fracture process. Adherend yield strength determined the joint strength, fracture state and failure modes when the failure occurred with yielding in the adherend. The fracture processes and strain evolutions in the bondline were found to be symmetric for the joints with the same adherends, while the maximum strain and crack appeared first on the lap end of the lower yield strength adherend for the joints with dissimilar materials. The study is expected to provide new insights into the design of multi-material joints with different thicknesses.