Warp direction fatigue behavior and damage mechanisms of centrally notched 2.5D woven composites at room and elevated temperatures

Abstract

Fatigue behavior, notch sensitivity and environmental effect are three of the principal concerns in composite applications, especially those for aeroengines that require mechanical fastening and fatigue resistance at elevated temperatures. As a new generation of woven composites, 2.5D woven composites (2.5DWC), have drawn increasing amounts of interest due to the excellent fatigue resistance of these materials. However, the lack of temperature-dependent fatigue explorations into centrally notched 2.5DWC (N-2.5DWC) significantly limits the engineering applications of these materials. Therefore, the objective of this paper is to investigate the temperature-dependent fatigue behavior of N-2.5DWC. Warp direction tension-tension fatigue tests of N-2.5DWC were performed at 20 °C and 180 °C for the first time. The fatigue lives and the related failure mechanisms were obtained experimentally. Interestingly, the fatigue life at the same temperature exhibited a sudden increase with a decreasing stress level. A temperature-dependent fatigue life prediction model was established, and the fatigue lives and damage propagation processes at various temperatures and stress levels were predicted. The predicted damage propagation process was a “L” shaped, which was consistent with the corresponding experimental fracture morphologies. Finally, the effects of temperature and warp arranged density on the warp direction fatigue life were discussed.