Fracture analysis of composite-titanium adhesively bonded joints under mode-I loading

In this paper, effects of adhesive, titanium surface roughness and manufacturing method on the fracture behaviors of composite-titanium adhesively bonded structures under mode I loading were studied. Experimental results showed that the maximum GIc obtained from specimen bonded with tougher adhesive was approximately 276% higher than another adhesive. Higher flatwise tensile strength and roller peel strength of tougher adhesive resulted in stronger resis-tance for crack growth in tougher adhesive itself, leading to adhesive or adherend fracture mode. The titanium surface roughness only affected the fracture performance of specimen with cohesive fracture, and the GIc of specimen with higher surface roughness was improved by 20%. As for manufacturing method, due to the surface treatment of composite, the secondary and co-bonded specimen presented fiber pull-out and matrix failure, respectively. As a result, the lower fracture energy required for fiber pull-out failure resulted that the secondary bonded specimen present nearly 50% smaller GIc than co-bonded specimen. The findings can provide detailed reference for design of composite-titanium bonded structures.