A novel macro-meso finite element method for the mechanical analysis of 3D braided composites

Finite element method based on the mesoscopic scale periodic unit-cell models was often employed to analyze the mechanical properties of 3D braided composites with obvious shell-core structural feature. To obtain the accurate predicted results, the contribution of the interior and surface unit-cell models to the overall mechanical properties should be considered for the finite element modeling. However, how to apply reasonable boundary conditions to the surface unit-cell model is still an interesting issue worth studying, which has great effect on the prediction precision of surface unit-cell model. Meanwhile, it is valuable to develop a novel macro-meso finite element modeling approach combined with the shell-core structural feature of 3D braided composites, which can contribute to improving the prediction precision and saving the computational costs. In this paper, a new integrated surface unit-cell model with the true yarn microstructure at the mesoscopic scale is proposed for 3D four-directional braided composites firstly. Secondly, a novel macro‑meso scale finite element modeling strategy for predicting the elastic properties and the micromechanical responses is presented. Thirdly, the key modeling procedures based on the solid unit-cell models are given. Finally, comparison of the calculated results with the available experimental data validates the effectiveness of the macro‑meso finite element model. The effects of the braiding angle and the fiber volume fraction of specimens on the elastic properties are discussed in detail. Discussion results indicate that the present macro‑meso finite element modeling strategy can be utilized to efficiently predict the mechanical performances of 3D braided composites.