Flexural Failure Behavior of Laminated Composites Reinforced with Braided Fabrics

The failure behavior and ultimate strength of laminated textile composites subjected to bending is analyzed. Each ply in the laminate is a braided fabric reinforced lamina, with a different braiding angle if necessary. The overall load shared by the lamina in the laminate is determined by means of the classical lamination theory. After discretizing the lamina into small elements, the internal stresses generated in the constituent fiber and matrix materials of the lamina are calculated based on a general micromechanics model, the bridging model. A stress failure criterion is applied to check the lamina failure status, by comparing the internal stresses with their critical values. Unlike an in-plane load situation where the ultimate failure of the laminate corresponds to its last-ply failure, the ultimate bending strength of the laminate generally occurs before its last-ply failure. Thus, the only use of a stress-failure criterion is no longer sufficient. A critical deflection condition must be employed also. Application to several laminated beams made of 8 layers of diamond braided HTA (T300) carbon fabrics and R57 epoxy matrix subjected to four-point bending has been made. The predicted ultimate strengths of the laminates agree well with our experimental measurements.