Effects of bondline thickness on Mode-I nonlinear interfacial fracture of laminated composites: An experimental study

Delamination or interfacial fracture is one of the most important issues for laminated composite structures. For the recent two decades, cohesive zone models (CZMs) have been receiving intensive attentions for modeling interfacial fracture of composite structures. Numerous global fracture tests have been conducted to measure the interfacial toughness of laminated composite plates. Some local tests have also been conducted to determine the interfacial traction-separation laws in adhesively bonded joints. However, most of these local studies focused on the interfacial fracture between metal adherends. Limited studies have addressed the local test of interfacial fracture between laminated composite plates. While it was well known that the bondline thickness has an important effect on interfacial fracture, very few studies investigated its effects on the local interfacial traction-separation laws of laminated composite plates in the literatures. In this work, both global and local tests are employed to investigate the effect of bondline thickness on the interfacial energy release rate, interfacial strength, and shape of the local interfacial traction-separation laws. Basically, the measured laws in the present work reflect the equivalent and lumped interfacial fracture behaviors which include the cohesive fracture, damage and plasticity. The experimentally determined traction-separation laws provide valuable baseline data for parameter calibrations in numerical models. The experimental results may also facilitate the understanding of bondline thickness dependent delamination of composite structures.