Damage and failure analyses of 3D4d braided composite shafts under torsional load and the effects of braid processing parameters on their torsional properties

Abstract 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, γ_r, 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 45^o.