| Three-dimensionally braided composites have superior properties, and they are widely used inhigh-technology fields such as aeronautics and astronautics etc. Study on the mechanical properties ofthree-dimensionally braided composites is very important. Because of its complicated structures, thereare many problems to be solved.In order to predict the macroscopic elastic constants of3D braided composites accurately，arepresentative volume unit cell for3D four-step braided composites with the periodic boundarycondition was established. The relationship between the elastic constants and the braided angle thefiber volume ratio were analyzed and discussed. It is shown that the elastic moduli of braidedcomposites depend mainly on the fiber volume ratio and the deviation angle between the principaldirection of yarns and the measure direction.The progressive damage behaviors was simulated by FEA software ANSYS. TheEshelby-Mori-Tanaka method was applied to calculate the stiffness matrix of damaged materials. Inorder to alleviate the mesh dependence, the size of the finite element and the crack were considered inthe damage evolution equation. The non-linear stress-strain relationship and the critical tensilestrength were obtained through numerical simulation, and the failure mechanism of composites withlarge braiding angle was also discussed. It is shown that the main failure modes of composites withlarge braiding angle are matrix cracking, transversely tensile and shear failure of yarns. And the mainfailure modes of composites with low braiding angle are yarns cracking.The results in the paper agreewell with the experiments in the literature.Finally, different criteria for the strength of materials were used and the damage unit cell ratio toall unit cells when the material failure occurs was obtained, and the strength of the material waspredicted.The result was compared with the strength by using progressive damage method, and theadvantages and the disadvantages were analyzed. |
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