Longitudinal compression fatigue properties of 3D five-directional braided composites at different temperatures

Abstract

3D braided composites are widely used in many areas due to their unique properties of high designability, excellent damage tolerance and integrality. Longitudinal properties of 3D five-directional braided composites (3D5dBC) deserve more extensive attention owning to addition of the fifth yarns for potential applications in marine at low temperature and aerospace at elevated temperature. In this work, longitudinal compression fatigue properties and failure mechanisms of 3D5dBC are investigated, where parameters of temperature, braiding angle and stress level are simultaneously considered. The results show that the composite at low temperature has better fatigue resistance ability, and fatigue resistance of small braiding angle composite is superior to that of large braiding angle composite. The strain change could be divided into three stages; the creep rate at stage II are similar respectively at −50 °C and 100 °C, which shows that strain change is temperature-independent. Meanwhile, the hysteresis loop at cycle of 3000 reveals that energy dissipation increases with the increase of stress level for large braiding angle composite. The failure modes of composite under longitudinal fatigue are shear expansion failure. At low temperature, brittle shear feature is more obvious. In addition, fiber/matrix interfacial debonding is more distinct at elevated temperature.