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 Model. 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. (C) 2013 Elsevier Ltd. All rights reserved.