Nonlinear numerical analysis of progressive damage of 3D braided composites

A tensile strength model to predict the damage initiationand propagation of 3D braided composites has been proposed based on therepresentative volume element by using the nonlinear finite element method.The geometrical unit-cell model considering the mutual contact and jammingof yarns was applied in the FEM model coupled with the periodicaldisplacement boundary conditions. In particularly, the nonlinear shearstress-strain behaviors of the yarns were considered in the model andHashin-type failure criteria were adopted to judge the occurring of damageevents of the yarns. Based on the degradation scheme of elastic mechanicalproperties, the simulation of the whole process of damage initiation,propagation and catastrophic failure of the structure was done in detail. Toverify the numerical model, two typical specimens with different braidingangle were selected to conduct the simulations. The calculated values by themodel are well agreed with the measured values. Numerical results verify theeffectiveness of the model. The effects of the shear nonlinearity of theyarn and damage accumulation on the nonlinear mechanical behavior of 3Dbraided composites were discussed. The conclusion has indicated that thenonlinear mechanical behaviors of the composites are affected remarkably bythe shear nonlinearity of yarns and accumulation of damages when thebraiding angle of the composites is increased.