The interfacial fracture of bonded structures is a critical issue for the extensive applications to a variety of modern industries. In the recent two decades, nonlinear fracture mechanics methods have been receiving intensive attentions for adhesively bonded joints. Extensive experimental efforts have been made to determine the toughness of adhesive joints. Several experimental studies have also been conducted to determine the interface cohesive law in bonded joints. However, very few studies investigated the effect of adhesive thickness on the interface cohesive laws. In the cohesive law, both fracture energy and the interfacial cohesive strength, as two critical parameters, have significant effect on the fracture behavior and joint’s structural capability. The present study presents the experimental investigation into how the adhesive’s thickness affect these two important parameters with the nonlinear fracture mechanics. At the mean time, the equivalent interface cohesive laws are experimentally determined for the bonded joints with various adhesive thicknesses. The experimental cohesive laws may provide valuable baseline data for simple analytical and numerical cohesive zone models. With the test results, the mechanism for the intrinsic fracture energy and plastic energy dissipation is discussed. Several other interesting conclusions are also obtained.

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