A multi-scale analysis method considering the realistic fiber structure for the nonlinear mechanical behavior of 3D needled twill composites

Three-dimensional needled twill composites have an extremely complex fiber structure, making investigating the nonlinear mechanical behavior challenging. This paper develops a multi-scale analysis method considering realistic fiber structure to predict the behavior. With the method, the damage evolution processes of different typical regions in the composites are analyzed in detail. Under in-plane loading, there is a platform area in the unneedled area, and the damage of the matrix and felt is distributed along the 45° direction in the plane. In the single-needled area, the damage of the matrix and felt occurs around the needled hole and expands perpendicularly to the load. The yarns in different typical areas primarily exhibit transverse damage, concentrated in the interweaving areas. Under out-of-plane loading, the damage of the yarn and matrix is distributed on the upper and lower surfaces, with the felt showing no damage. In addition, a periodic unit cell model including different typical areas is built to analyze the nonlinear mechanical behavior of composites. The stress-strain curves predicted by the model are aligned well with the experimental results. The developed method effectively predicts the nonlinear mechanical behavior of composites, captures the damage evolution mode of different typical areas, and provides guidance for the application of composites.