Experimental study on the bending fatigue behaviors of 3D five directional braided T-shaped composites

Abstract

The static three-point bending properties and cyclic bending fatigue performances of three-dimensional five-directional braided T-beam composite (3D5DBTC) have been investigated at room temperature. The fatigue life of 3D5DBTC under different stress levels was analyzed based on the obtained S–N curves. The load–displacement hysteresis loops curves and stiffness degradation curves were recorded to reveal the relationship between stiffness degradation and damage evolution. It is shown that there were three distinct stages corresponding respectively to matrix cracks, interface debonding, and fiber breaking in the whole fatigue loading. In addition, to understand the ultimate fracture failure mechanism of 3D5DBTC under the different fatigue loading conditions, the damage morphologies of 3D5DBTC after fatigue testing were observed by macrographs and SEM micrographs. The matrix crack and the resin–yarns interface debonding occurred on the flange while fiber breakages occurred in the web. Meanwhile, macrographs and SEM images confirm that fiber breaking is the dominant damage under the high stress level, while matrix cracking and interfacial debonding are the main failure modes at low stress level.

Keywords:

• Three-dimensional five-directional braided T-beam composite (3D5DBTC)
• bending fatigue
• stiffness degradation
• damage mechanism

Acknowledgments

The authors acknowledge the financial supports from the Chang Jiang Scholars Program and National Science Foundation of China (Grant Number 51675095 and 11572085). The financial supports from Foundation for the Fok Ying-Tong Education Foundation (Grant No. 141070), Shu-Guang project (Grant No. 14SG31) supported by Shanghai Municipal Education Commission and Shanghai Education Development Foundation, the Fundamental Research Funds for the Central Universities of China and DHU Distinguished Young Professor Program are also gratefully acknowledged.