A novel analysis method for mechanical properties of 3D needled twill composites based on virtual fibers

Compared with the traditional 3D needled composites with non-woven structure, the composites with twill layers have an extremely complex mesostructure. Three representative regions are divided based on the mesostructure observation of 3D needled twill composites. At the same time, the needling process of the 3D preform is simulated based on the digital element method, and the fiber deflection formulas in the needled region are built. Considering the distribution of different needling points, the periodic unit cell models of 3D needled twill composites that include three representative regions are established to predict the mechanical properties. It is verified that the results predicted by the proposed model agree well with the experimental data. Moreover, the effects of different needling angles and needling points on the mesostructure and mechanical properties of the composites are further studied, which helps guide the design and manufacture of 3D needled twill composites.