Fracture of plastically-deformed, adhesively-bonded structures: Experimental and numerical studies.

Abstract

Developing an understanding of unstable crack growth in the presence of plasticity is crucial for modeling energy management during crashes for adhesive joints in automotive structures. Of general concern in this study is the rate dependence of the adhesive properties. Of particular concern is the possibility of catastrophic loss of toughness at rates that might be appropriate to vehicle crashes. Experimental observations for the transitions between mode-I quasi-static and dynamic fracture in a plastically deforming steel/adhesive/steel structure is presented. Numerical studies with cohesive-zone models provide a powerful approach for simulating the response of adhesive joints subject to both quasi-static loading and relatively high rates of loading. The mode-II interfacial toughness and interfacial strength were determined at different rues. These parameters were then combined with the previously-determined mode-I parameters within a cohesive-zone model to analyze mixed-mode fracture of the joints, which exhibited both quasi-static and unstable fracture. While a model for the transitions to dynamic fracture has not been developed, the cohesive-zone model provided accurate predictions for the behavior of the joints with each type of failure. The values for the toughened and untoughened modes of crack propagation provided bounds for predicting the behavior of the bonded joints under various rates of loading, up to the impact conditions that could be appropriate for automotive design.