Study on in-plane compression properties and numerical modeling of three dimensional five-directional braided composites

Delamination phenomenon often occurs on traditional laminated composites while 3D five-directional braided composites (3D5dBC) could avoid this defect in practical application. In this work, the mechanical properties and failure mechanisms of 3D5dBC with different braiding angles are investigated at room temperature under transversal and longitudinal compression via experiments and finite element analysis (FEA) simultaneously. Meanwhile, the compression properties at elevated temperature are also researched. It is found that mechanical properties of composites under longitudinal compression are superior to those under transversal compression. Composite with small braiding angle possesses higher strength and modulus comparing to those of large braiding composite. Moreover, at room temperature, 3D5dBC exhibits 45º shear crack failure mode under transversal compression originated from matrix cracking, fiber failure along Z-direction obtained from FEA, and interfacial debonding; Under longitudinal compression, the structure shows shear expansion failure feature due to thorough fracture of axial yarns along L-direction, braiding yarns fracture along L-, T- and Z-direction, and matrix cracks obtained from FEA. With temperature increasing, interfacial debonding of fiber/matrix gets obvious. The microscopic failure modes and process at room temperature are well explained by FEA method.