Ductile double-lap joints from brittle GFRP laminates and ductile adhesives, Part I: Experimental investigation

Quasi-static axial tension experiments were performed in a laboratory environment on adhesively-bonded double-lap joints from pultruded GFRP laminates. Full-scale specimens were investigated to prevent size effects. Ductile polyurethane and acrylic as well as brittle epoxy adhesives were applied to connect brittle GFRP adherends. The visco-elastoplastic/ductile and visco-elastic/brittle stress–strain behavior of adhesives was defined. It is shown that joint stiffness depends non-linearly on the ratio of adhesive to adherend modulus, and approaches a threshold value with increasing adhesive modulus. Ductile joints with plasticized adhesives develop uniform load transfer over the joint length with increased strength as compared to joints with brittle adhesives. In contrast to joints with brittle adhesives, the joint strength of ductile joints with plasticized adhesive increases almost proportionally with increasing overlap length. Axial strains are almost uniformly distributed across the joint width and allow for a 2D analysis.