Ductile double-lap joints from brittle GFRP laminates and ductile adhesives, Part II: Numerical investigation and joint strength prediction

Joint analysis using a non-linear finite element model has been performed to analyze the effects of adhesive ductility on the stiffness and strength of full-scale adhesively-bonded double-lap joints composed of brittle pultruded GFRP laminates. Experimental and numerical results of joint and specimen elongations and axial strains in the bondline compared well. Calculated stress states at failure location inside the adherends showed that plastification of ductile adhesives provide uniform load transfer leading to increased joint strength. Joint strength increases almost linearly with increasing overlap length. Flexible and stiff joints are defined depending on the ratio of adhesive-to-adherend modulus. Flexible joints exhibit lower stiffness than the adherends, while stiff joints provide continuity of structural stiffness. The strength of ductile adhesively-bonded joints was predicted by extending an existing through-thickness shear-tensile-interaction failure criterion developed for brittle joints with epoxy adhesive.