Crack initiation in single lap joints: effects of geometrical and material properties

Brittle failure of adhesively bonded single lap joints is considered in this paper. A coupled stress and energy criterion in the framework of finite fracture mechanics is employed to study crack initiation by means of a numerical model presented by Hell et al. (Eng Fract Mech 117:112–126, 2014). Two different formulations of the coupled criterion are compared and the effect of geometrically nonlinear bending deformation of the adherends is analysed. A comparison to experimental results on the effect of the overlap length for single lap joints with composite adherends is given, showing a very good agreement of the failure load predictions. A detailed study of the effects of the geometrical and material parameters of a single lap joint configuration is given. As the energy release at crack formation is considered, the size effect of the adhesive layer thickness is covered correctly. The paper closes with an analysis of the effect of the unbonded adherend length. An approximate explicit expression for a minimum unbonded adherend length is given, which is required to optimize joint designs and to allow for the study of individual parameter effects in numerical and experimental studies.

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