Determination of bridging laws for SMC materials from DENT tests

A bridging law (or cohesive zone law) approach is employed to evaluate the fracture of double edge notched tensile (DENT) specimen from two SMC materials (Std-SMC and Flex-SMC) with considerable difference in fracture characteristics. Linear- and non-linear FEM was used to separate volumetric body contributions and true crack opening from measured displacements (measured with extensometer) over the cracked region. We found that extrinsic non-linear material response gave a significant contribution to measured displacements. The paper also considers the influence of specimen dimensions on the characteristics of fracture. This is of great importance since stable crack growth is required in order to allow a complete determination of the bridging law in a single experiment. By applying corrections for volumetric displacements in the data reduction scheme we were able to estimate the bridging laws of the two SMCs respectively. They were found to be of decreasing nature and two distinct regions were identified. For small (delta) , a steeply decreasing part where debonding and fiber fracture are major micro-scale failure mechanism, is identified. At larger (delta), a transition to a less steep bridging law response is observed. Pullout friction governs the bridging law at that stage.