A maximum stress at a distance criterion for the prediction of crack propagation in adhesively-bonded joints

The present work relates to the numerical prediction of the mode I failure of metal-to-metal adhesive joints under 2D quasi-static, steady-state conditions by means of a criterion based on attaining a critical value of maximum principal stress, deltac , at a critical distance, rc , ahead of the crack tip. The model, which fully accounts for the complex elastic-plastic fields inside the adhesive, predicts very accurately the failure of the structural adhesive (i) over a wide range of the thickness of the adhesive layer from 0.1 to 1 mm, and (ii) for two very different test geometries: namely the linear elastic fracture-mechanics (LEFM) tapered double-cantilever beam (TDCB) test and the elastic-plastic fracture-mechanics (EPFM) wedge-peel test. This approach is applied to an epoxy-based structural adhesive where failure occurs cohesively in the adhesive layer. Additional non-dimensional parametric studies have been performed to unravel the link between the geometric effects, the various contributions to the fracture energy, the local stress and strain fields, and the material parameters. It is shown that the proposed criterion based on attaining a critical value of the maximum principal stress at a critical distance ahead of the crack tip provides a better predictive model than that based upon using a cohesive zone model approach.

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