Properties Of Three-dimensional Braided Composites Research Articles

Mechanical analysis of three-dimensional braided composites by using realistic voxel-based model with local mesh refinement

The elastic and failure analysis of three-dimensional braided composites is conducted by using realistic geometry model with local mesh refinement. The realistic geometry model is reconstructed by using micro computed tomography images. The voxel meshes are utilized to overcome the difficulties of mesh discretization for realistic geometry model of three-dimensional braided composites with complex meso-geometrical configurations. In order to improve the computational efficiency, the local voxel meshes at the braid yarn boundaries are refined to capture the detailed geometries of braid yarn and reduce the number of mesh. The stress averaging technique is applied to alleviate the local artificial stress spurious introduced from voxel meshes at braid yarn boundaries. Three kinds of computation models are used to predict the tensile properties of the braided composites, which are also compared with experimental results. The effects of braid yarn twist angle and mesh sizes on the predicted tensile behavior of the braided composites are studied further. A systematic way is provided to analyze mechanical properties of three-dimensional braided composites by using realistic voxel-based model.

Finite element prediction of the impact compressive properties of three-dimensional braided composites using multi-scale model

This paper presents a comprehensive study aimed at the compressive properties of three-dimensional (3D) braided composites subjected to quasi-static and high strain rate loadings using finite element method from fiber/matrix scale to composite scale. It focuses on a computationally efficient multi-scale methodology for prediction of the effective elastic properties and the failure strength of 3D braided composites. First, finite element models with strain rate sensitive elasto-plastic constitutive relationship and ductile and shear failure criterion were established to investigate the mechanical properties and failure mechanism. Second, the failure mechanism in micro-scale fiber/matrix was investigated. The mechanical properties of the interior unit cell, surface unit cell and corner unit cell were predicted and compared, which shows that the surface and corner region of braided preform play an important role during both quasi-static and high strain rate loading. The results obtained from the whole structure heterogeneous composite model and the homogeneous composite model were also analyzed and compared. Finally, the numerical results were verified by the experimental data and the results are encouraging. This method can provide an important guidance for evaluating the mechanical properties and selecting structural parameters for braided composites.

Experimental investigation of cut-edge effect on mechanical properties of three-dimensional braided composites

Experimental characterization of the effect of cut-edge on the tensile, compressive and flexure properties in the braiding direction of the 3D braided composites is presented. The geometrical microstructure models of the uncut-edge and cut-edge composites are established for calculating the remainder lengths of braider yarns in the composites. The integrity of fiber architecture as reinforcement is destroyed for the cut-edge composites. So in order to determining the loss of the mechanical properties for the composites specimens, four schemes of cut-edge are discussed comparatively, single-edge cut on the width, single-edge cut on the thickness, both-edge cut on the width, edge cut on the thickness and width. Experimental results are coincident with the deduction based on the remainder lengths of braid yarns. The cut-edge on the width of specimen barely affects the bending properties of coupons, whereas, cut-edge on the thickness lowers the flexural modulus. The flexural modulus is reduced more when surface cut on the thickness is carrying tensile load under bending.

Mechanical properties of three-dimensional braided composites

Recently developed digital element approach, which treats textile composite manufacturing process as a nonlinear solid mechanics problem, was successfully used to investigate the complicated microstructure of 3D braided rectangular preform. The yarns interaction and cross-sectional deformation, which were neglected in traditional topological model, could be analyzed exactly. Results showed that yarns inside 3D braided preform were curvy, which was opposite to the straight-yarns assumption of topological model and, yarns curvature inside the preform, which was very difficult to be explored before both experimentally and theoretically, was investigated numerically. After that, the mechanical properties of 3D rectangular braided composites, such as tensile stiffness, shear stiffness and Poisson ratio were calculated through the volume-average-compliance method. Comparison was conducted for those from the topological model and digital element approach, and topological model was found to underestimate greatly both the tensile stiffness and shear stiffness.

A homogenisation scheme and its application to evaluation of elastic properties of three-dimensional braided composites

Abstract A homogenisation scheme is developed to evaluate the elastic properties of three-dimensional (3-D) composite materials. The requirement of continuity at internal interfaces is satisfied in the scheme. The effective stress–strain relation is first derived for a particular stratified composite with straight internal interfaces. Then, a more general case with curved interfaces is discussed. Two special cases, namely, unidirectional fibre reinforced composites and particulate reinforced composites are evaluated using the scheme. It is shown that the predictions are in good agreement with experimental data. Furthermore, this homogenisation scheme is applied to 3-D braided composites to predict the elastic properties. It is again shown that the predictions are in good agreement with experimental results.

Structure and properties of three-dimensional braided composites including axial yarns

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