A novel shell‐based hierarchical multiscale model for studying three‐dimensional four‐directional braided composite shafts

Abstract The mechanical properties of three‐dimensional (3D) braided composites are related to damage evolution. However, the multi‐scale damage mechanism of 3D braided composite shafts remains unclear. The main purpose of this article is to propose a shell‐based multiscale finite element model for effectively predicting the compressive and torsional properties of 3D four‐directional (3D4d) braided composite shafts. Considering the relation between equivalent ply angles and yarn structures, the multiscale model was developed based on a universal tubular unit cell. The equivalent ply angle was derived through the yarns' local braiding and horizontal orientation angles, and the elastic properties of each equivalent ply were derived through the stiffness averaging method. Both derivations were achieved by creatively utilizing deformation gradient theory and Nanson's formula from continuum mechanics. LaRC04 failure criteria and energy‐based damage evolution law were implemented to characterize the equivalent UD‐ply's damage behaviors. The proposed model was validated experimentally, and good agreements were observed between the failure morphologies and load–displacement curves of FEA and experimental results. The results show that the fiber tension and compression damages are the major failure modes of 3D4d braided composite shafts under compressive and torque loads, respectively. Finally, a parametric study was carried out and compared with that from other literature to clarify the meaning of this article in relevant studies. It provides an efficient and useful tool for the design and manufacturing of 3D4d braided composite shafts with desirable mechanical properties. Highlights A shell‐based hierarchical multiscale model is developed for 3D braided composite shafts. An analyzing method is developed to investigate the tubular yarn structures. A large‐scale torsional experimental scheme is developed.