Finite element analyses of four-step 3D braided composite bending damage using repeating unit cell model

This paper reports bending deformation and damage of four-step 3D braided composite materials from experimental and finite element analyses approaches. In experimental, the three-point bending deformation and damage of the braided composite materials were observed and the load–deflection curves were obtained for analyzing the bending behaviors. In finite element analyses, three types of repeating unit cell geometrical models were established to characterize the microstructures of 3D braided composite materials. The critical damage area failure criteria were employed in the finite element analyses. The repeating unit cell geometrical models and the finite element analyses were verified with the experimental results. The influences of structure parameters in the repeating unit cells on the bending behaviors were analyzed. It was found that the volume fraction of surface and corner repeating unit cells were around 30%, and their elastic modulus along axis Z was about 5 times that of inner repeating unit cell. The surface and corner repeating unit cells play the important role for the entire structure under bending and cannot be neglected.