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A new alternative calculation procedure is developed to quantify the effect of yarn distortion characteristics on the mechanical properties of three-dimensional (3D) braided carbon/resin composites. Firstly, the multi-type yarn distortion characteristics factors including path, cross-section shape and cross-section torsion effects are described based on the stochastic theory. Then, the multiphase finite element method is employed to overcome the complex discretization in traditional numerical analysis, and the parametric studies including multi-type yarn distortion and different braided geometrical parameters on the resulting mechanical properties are performed. It is shown that the proposed procedure can simultaneously capture the yarn path and cross-section distortion characteristics caused by the mutual squeeze of component materials, which is difficult to characterize by experimental methods. In addition, it is found that even small distortions of yarn may significantly affect the mechanical properties for 3D braided composites, and the 3D braided composites with different braiding geometric parameters will show different sensitivity to the distortion characteristics factors of yarn. The procedure, which could be implemented into commercial finite element codes, is an efficient tool for the design and structural optimization analysis of a heterogeneous material with anisotropic properties or complex geometries. [ABSTRACT FROM AUTHOR]

A new multiscale method was developed for the thermo-mechanical performance analysis of three-dimensional (3D) braided composites. This method is the extended of multiscale asymptotic expansion homogenization (MAEH) method and multiphase finite element (MPFE) approach. The analysis was performed under a representative unit cell (RUC) scale and tow architecture scale. The effective thermo-physical properties of 3D braided composites were predicted. The bending mechanical response under thermal and mechanical loading was determined by the present multiscale finite element method. The effects of braiding angle and temperature difference on the thermo-mechanical behaviors were studied. The three-point bending tests were performed under thermal and mechanical loading and the measured results were compared to the predicted ones to illustrate that the new method is effective and valid for predicting the thermo-mechanical performance of 3D braided composites. [ABSTRACT FROM AUTHOR]

This paper investigates the elastic behavior and failure strength of three-dimensional braided composites by using a multi-scale finite element method. The analyses are performed under the representative unit cell scale and tow architecture scale. The heterogeneous material structure in a RUC is modeled by the multiphase finite element method. Three special element types, called yarn element, matrix element and mixed element, are derived. The correlation between different scales is derived based on the continuum mechanics and homogenization method. Effective modulus of 3D braided composites is predicted solely from the corresponding constituent properties and braided geometrical parameters. The bending strengths are determined by the failure criteria of the components. The predicted results compare favorably with available experimental data. Parametric studies are also performed to examine the effect of braiding angle on the resulting mechanical properties. [ABSTRACT FROM AUTHOR]