Effect of Bondline Thickness on the Tractionseparation Laws of Adhesively Bonded Joint

A number of existing and emerging industrial applications are dependent on layered substrates through adhesive bonding. The interfacial fracture of adhesively bonded structures is a critical issue for their extensive applications to a variety of modern industries. In the recent two decades, cohesive zone models (CZMs) have been receiving intensive attentions for fracture problems in adhesively bonded joints due to its fairly simple and accurate predictive ability. In CZMs the nonlinear interfacial fracture behaviors are described by the traction-separation laws (also referred to as cohesive laws). The cohesive laws represent the local constitutive behavior, instead of the global parameter, such as toughness. While numerous global tests have been conducted to measure the interfacial toughness of adhesive joints, limited local tests have been conducted to determine the interfacial tractionseparation laws or interfacial cohesive laws. Among the limited local tests in some recent experimental studies, very few studies have considered the effects of adhesive thickness on the local interfacial traction-separation laws. In the present work, within the framework of nonlinear fracture mechanics, comprehensive experimental studies are conducted to investigate the effect of adhesive layer thickness on the local nonlinear interfacial behaviors. The fracture tests of adhesive joints with various adhesive layer thicknesses were conducted under different fracture modes: pure Mode-I (peel fracture), pure Mode-II (shear fracture), and mixed Mode I/II. The experimentally determined interfacial traction-separation laws provide valuable baseline data for parameter calibrations in numerical models. The current experimental results may also facilitate the understanding of adhesive thickness dependent interface fracture of bonded joints.

Keywords: Adhesive thickness, Bonded joints, Cohesive law, Cohesive strength, Cohesive zone model, Interfacial strength, Plastic zone, Toughness.