Abstract

A microstructure model of 2-D braided composite is developed. The fiber volume and crimp angle are evaluated by this model and are compared with experimental results. The maximum fiber volume fraction is also obtained. Effective stiffness of 2-D braided composite is obtained in a close form by the analysis of elastic deformation energy in repeat-unit-cell of braided composites. Effective stiffness consists of contributions of axial yarn, braiding yarn, and matrix material. Each of them takes a different weight in the effective stiffness. The weights of contribution of axial yarn, braiding yarn, and matrix material are $\rm\chi V\sb{f}/k$, (1-$\chi$)$\rm V\sb{f}/k,$ and (1-V$\rm \sb{f}/k)$ respectively, where $\rm V\sb{f}$ is the fiber volume fraction, $\chi$ is the axial yarn content in a braided composite, and k is the filament packing fraction. The results of effective stiffness from theoretical prediction are very good as compared with test data from experiments. Effective coefficients of thermal and hygro expansion are analyzed by virtual energy method. The independent parameters in design and analysis of braided composites are successfully separated from all other parameters. This greatly reduces the difficulties of design and analysis of 2-D braided composites. Objected-oriented Matlab programs are built for the parameter analysis.