Orthogonal Study on Mechanical and Tension–Tension Fatigue Properties of Flax/Glass Fiber Hybrid FRP Composites

Nowadays, fiber-reinforced polymer (FRP) composite has already become the alternative structural material to traditional reinforced concrete (RC) because of the characteristic of lightweight and high strength, better corrosion and fatigue resistance and so on. However, the frequently used synthetic FRP composite products also exist the defects of being expensive and harmful to the environment and human health. In this paper, the epoxy resin-based composite plates were prepared through the hand layup molding, which used the flax fiber fabric modified by the 1% NaOH solution and glass fiber fabric. The influence mechanism of the three factors with fiber orientation angle, stacking sequence and hybrid ratio on the tensile, flexural and tension–tension fatigue properties of hybrid composites was studied by orthogonal tests. Moreover, the fracture morphology of the composites was observed by the scanning electron microscope (SEM). The results showed that the fiber orientation angle had the most significant effect on the tensile, flexural and tension–tension fatigue properties of the composites, followed by the hybrid ratio, and the influence of the stacking sequence could be ignored. In addition, the SEM images showed that the interfacial debonding between glass fiber and matrix, as well as the pull-out and brittle fracture of flax fiber, was the main failure modes of the hybrid composite under the tensile load; the pull-out, folds, buckling and a few cracks appearing of flax fiber, as well as the debonding and delamination of glass fiber, were the primary failure modes of the hybrid composite under the flexural load.