This paper presented the numerical and experimental studies on the torsional properties of 3D braided composite shafts. The torsion test was first conducted, then a parametric tubular unit cell model was constructed based on geometric mapping relations to detail the micro geometries of the shafts. The local yarn orientations were derived using finite deformation theory, and the 3d Hashin failure criterions were adopted to simulate the progressive damage behaviors of the shafts. The predicted results were in good agreements with the experimental ones, which validated the FE model. Based on the FE results, the damage was analyzed in detail, it was found that the transverse shear-tension damage of longitudinally compressive yarns was critical for the failures of 3D4d braided composite shafts under torsional load. The surface damage initiated first, and then propagated into the internal structure, while the internal damage was much severe in the final failure morphology. The effects of braid processing parameters (M, N, γr, and r1,) on the torsional properties were also reported. A dependency of increasing then decreasing was confirmed by the simulation results for all four parameters, and it was found that the peak values could be achieved when the average braiding angle was around 45o .

本文对3D编织复合材料传动轴的扭转特性进行了数值和实验研究。首先进行了扭转试验，然后基于几何映射关系构造了一个参数化的管状单胞模型，以详细说明轴的微观几何形状。利用有限变形理论推导了局部纱线的取向，并采用3d Hashin破坏准则模拟了轴的渐进式损伤行为。预测结果与实验结果吻合良好，验证了有限元模型。根据有限元分析结果，对损伤进行了详细的分析，发现纵向压缩纱线的横向剪切张力损伤对于3D4向编织复合材料传动轴在扭转载荷下的破坏至关重要。表面损伤首先开始，然后传播到内部结构中，而内部损伤在最终破坏形态上要严重得多。还报道了编织工艺参数（M，N，γr和r1）对扭转性能的影响。所有4个参数的仿真结果证实了先增大后减小的相关性，并且发现当平均编织角约为45度时可以达到峰值。