Static and fatigue behavior of basalt fiber-reinforced thermoplastic epoxy composites

Abstract

The static, fatigue properties and their damage mechanism of basalt fiber-reinforced thermoplastic epoxy polymer composites are investigated. The stress–life curves and stiffness degradation under long-term cyclic loading were tested for basalt fiber-reinforced thermoplastic epoxy polymer. An advanced fatigue loading equipment combined with in situ scanning electron microscopy was used in the tests to track the damage propagations and analysis the fracture surfaces of all specimens. Results were also compared with those of thermosetting epoxy-based basalt fiber-reinforced polymer composites. The results show that the basalt fiber-reinforced thermoplastic epoxy polymer has good interface properties between the fiber and new thermoplastic epoxy, which results in high tensile strength and ductility. Different degradation rates of low- and high-cycle fatigue loads are observed for the basalt fiber-reinforced thermoplastic epoxy polymer composites. Under high fatigue stress levels, a high degradation rate of the fatigue life is found because the dominating damage pattern showed fiber fractures. At low and medium fatigue stress levels, the damage pattern is dominated by matrix cracking and interface debonding, which results in a low degradation rate of the fatigue life. A bilinear phenomenological fatigue model has a higher accuracy for fitting the stress–life data than linear fatigue models. In addition, 80–90% stiffness degradations are observed before failure for all stress levels at a stress ratio of 0.8. Furthermore, compared with thermosetting epoxy-based basalt fiber-reinforced thermoplastic epoxy polymer, the basalt fiber-reinforced thermoplastic epoxy polymer has similar static strength and similar fatigue life at high-stress levels. However, at low-stress levels, the fatigue life of the this polymer is much higher than that of thermosetting one.