Static and bending fatigue properties of ultra-thick 3D orthogonal woven composites

Nowadays, ultra-thick 3D woven composites have great potential applications in aerospace, maritime and infrastructure fields. Static and dynamic mechanical data for 3D ultra-thick composites are on a high demand by industry. In this study, a 15 mm ultra-thick 3D composite reinforced with woven glass fabric was fabricated, and the static and bending fatigue properties were analyzed. For comparison, the 2D composite with almost the same thickness and fiber volume fraction with the 3D composite was also fabricated. The results showed that the 3D-warp and 3D-weft samples have 21% and 5% higher normalized tensile strengths, 28% and 9% higher normalized tensile moduli, 29% and 25% higher normalized compression strengths, 18% higher and a similar normalized compression moduli compared with those of the 2D laminated sample, respectively. The superior in-plane properties of the 3D composite to the 2D laminates were due to crimp-free states of the warp and weft yarns in the 3D orthogonal structure. In the bending test, the 3D-warp and 3D-weft samples both have 42% higher normalized flexure strengths, 32% and 28% higher normalized flexure moduli than those of the 2D sample, respectively. Meanwhile, the failure mechanisms and fracture modes are also analyzed for the different mechanical tests of the two types of composites. In bending fatigue test of 3D composite, a linear regression model is used to predict the residual stiffness of the composite. The experimental results of fatigue residual stiffness reduction of both directions agree reasonably well with the predictions of the model.