Interlaminar toughness characterisation of 3D woven carbon fibre composites

The addition of reinforcement in the through thickness direction using three-dimensional (3D) weaving techniques has been shown to improve the delamination toughness of composite materials, mitigating the reduced out of plane performance of traditional composite materials. At present, the optimum architecture for improving delamination resistance is uncertain. To address this, three geometries of 3D woven carbon fibre reinforced epoxy composites were evaluated in mode I using the double cantilever beam test method. Mode II testing was also carried out using the end loaded split and four-point end notch flexure test methods. For large delaminations (i.e. when the R curve reaches its plateau value), an orthogonal weave is found to be most effective in resisting delamination propagation in mode I and is comparable to the layer to layer architecture in mode II. In all cases, an angle interlock weave appears to be less effective than either the orthogonal or layer to layer weaves.