Finite Element Modeling Based On Composite Damage Theory For The Strength Prediction of 3D Braided Composites Structures

Abstract

Finite element analysis for the strength prediction of 3D braided composites structures are presented in this paper. A strength analysis model was established to investigate the strength characteristics of the 3D braided composites. Repeated unit-cell (RUC) model was used in this model to describe the microstructure of 3D braided composites and differences between yarn configurations in corner, surface and interior RUCs were considered. Composite damage model were introduced into the yarns of the RUCs in the analysis model and the macroscopic failure and damage evolution of the 3D braided composites structures were characterized by the damage of yarns by nonlinear homogenization method. To validate the veracity of this model, a user defined material subroutine (UMAT) was developed to introduce this model into the finite element analysis software and the damage progression of a 3D braided composite structure under three-point bending was simulated. Good agreements were achieved in the load- deflection curves and damage morphology between experimental and numerical results. effect of yarn distortion was considered in the simulation. Dong et al. (9) simulated the non-linear behavior of cumulative damages of 3D braided composites by the method of Asymptotic Expansion Homogenization (AEH) and the influence of face cell and corner cell and proper boundary conditions on each kind of unit cells were studied in his paper. Most of the investigations on the elastic and strength properties of 3D braided composite were based on simple loading modes such as unidirectional tension and compression, in which no macroscopic model needs to be built and the mechanical properties of 3D braided composites can be characterized by the repeated unit cell, providing a way to consider the effect of microstructure details on the macro-scale property predictions. However, this method is not suitable for investigating the macroscopic strength properties of 3D braided composites structures as the stress distribution inside the braided composite structures may be non-uniform and cannot be characterized by a single unit cell. A strength analysis model based on the RUCs was established in this paper. The repeated unit-cell (RUC) model was used to simulate the mechanical properties of 3D braided composites and three kinds of RUCs were considered based on the different yarn configurations in the corner, surface and interior regions of braided composites. Three-dimensional composite damage models were applied for the yarns in RUCs to simulate the macroscopic nonlinear response of braided composites. A user defined material subroutine (UMAT) was developed to introduce this method into the numerical simulation. The strength analysis of a 3D braided composite structure was made to verify the validate of the model and good agreements were obtained between numerical prediction and experimental results.