Progressive failure process of adhesively bonded joints composed of pultruded GFRP

Adhesively bonded joints are being used increasingly in civil engineering structures, especially for joints comprising pultruded glass fiber reinforced polymer (GFRP) laminates. The layered material architecture, however, leads to a complex delamination failure within the pultruded material, thus necessitating understanding of the progressive failure mechanism of such joints under axial tensile loading. In this work, adhesively bonded joints composed of pultruded GFRP laminates, including double and stepped lap joints, were experimentally investigated. The static strengths of joints were obtained and the failure mechanism was understood. Crack propagation and back face strain gages were successfully employed to identify crack initiation and describe crack propagation, even though the failure mechanism was always sudden and brittle. The dominant failure mode for both types of joints was a fiber-tear-off failure that occurred in the mat layers of the GFRP laminates. The critical strain energy release rate was calculated. Different values were obtained for the two joint types due to different combinations of fracture modes.