Failure and damage characterization of (±30°) biaxial braided composites under multiaxial stress states

This paper focuses on the mechanical characterization of (±30°) 2×2 biaxial braided composites under multiaxial stress states. Off-axis experiments in tension and compression were used to introduce multiaxial stresses in the material. The characterization was focused on nonlinear deformation and failure behavior: loading/unloading of the specimen was used to identify the mechanisms for nonlinear deformation and a high-speed-camera is used to record the failure mode of the specimen. It has been found that the failure modes are mainly dominated by shear-induced transverse cracking. A dependency of the failure mode on the transverse yarn stress was observed. The deformation was strongly nonlinear, and dominated by the shear-behavior of the yarns. An equivalent laminate model was employed for failure prediction, showing that the failure of the biaxial braided composites can be predicted accurately, when the knockdown induced by yarn waviness is considered in the material input parameters.