1 Risø National Laboratory for Sustainable Energy, Technical University of Denmark
The influence of different fibre sizings on the strength and fracture toughness of composites was studied by investigating the characteristics of fibre cross-over bridging in DCB specimens loaded with pure bending moments. These tests result in bridginglaws, which are obtained by simultaneous measurements of the crack growth resistance and the end opening of the notch. The advantage of this method is that these bridging laws represent material laws independent of the specimen geometry. However, theadaption of the experimentally determined shape to a numerically valid model shape is not straight forward, and most existing publications consider theoretical and therefore simpler softening shapes. In this article, bridging laws were implemented intoan interface element in the UEL user subroutine in the finite element code ABAQUS. Comparison with different experimental data points for crack opening, crack length and crack shape show the sensitivity of these results to the assumed bridging law shape.It is furthermore shown that the numerical predictions can be used to improve the bridging law fit. One shape with one adjustable parameter then fits all experimental data sets.