Tensile properties and failure mechanism of 3D woven composites containing holes of different geometries

The open-hole tension (OHT) properties and failure processes of three-dimensional (3D) woven composite plates with circular, racetrack, and square holes were investigated in this study through experiments and finite element (FE) modeling. Tensile tests were performed on unnotched and notched specimens and measured via digital image correlation (DIC) to record the full-field strain fields, while micro-computed tomography (micro-CT) was employed to obtain the fracture morphologies. To predict the OHT performance, stress concentration factor (SCF), and damage propagation processes of the notched specimens, progressive damage analysis based on the FE model of a macro-meso coupling model was implemented on three open-hole plates. It was found that the OHT strength of 3D woven composites was reduced by approximately 35% compared with that of the unnotched specimen, whereas the modulus remained almost unchanged. The hole shape significantly influenced the strain distributions but had no perceptible effect on the OHT strength. The SCF of the specimen with a circular hole was 36% higher than those cases of the racetrack and square holes. Moreover, the hole-edge stress concentrations were mainly distributed on the warp yarns and became a cause for early failure. The major failure modes near the hole edge were warp breakage and pull-out.