Modeling effects of asymmetry and fiber bridging on Mode I fracture behavior of bonded pultruded composite joints

The fracture behavior of adhesively-bonded pultruded double cantilever beam specimens was experimentally investigated. The pultruded adherends comprised two mat layers on each side with a roving layer in the middle. An epoxy adhesive was used to form the double cantilever beam specimen. The crack propagated along paths away from the symmetry plane and was accompanied by fiber bridging. Finite element models were developed to quantify the effects of asymmetry and fiber bridging on the fracture energy. The virtual crack closure technique was used for calculation of the fracture components at the crack tip and an exponential traction–separation cohesive law was applied to simulate the fiber bridging zone. The asymmetry was due to the relatively thick adhesive layer and the depth of the pre-crack. However, the Mode II fracture component obtained was less than 10% of that of Mode I. The fiber bridging was found to contribute significantly, by up to 60%, to the total strain energy release rate. Although the cohesive zone model developed requires experimental data for calibration of the model, it can subsequently be used for simulating progressive crack propagation in other joint configurations comprising of the same adherends and adhesive.

► The fracture of adhesively-bonded DCB specimens was investigated.
► FE models developed to quantify the asymmetry and fiber bridging effects.
► Use of a resin interlayer diminishes the calculation sensitivity.
► Zero-thickness cohesive elements used to model the fiber bridging.
► The separation of the fracture parameters was successfully performed.