Three-cell model and 5D braided structural composites

A three-cell model is proposed, constructed on the basis of the microstructure analysis of braided structural composites which can be produced by four-step braiding (four-direction, 4D) without or with the addition of uniaxial reinforced yams. This last process is called five-direction (5D) braiding. From this model and with the aid of a yarn/matrix interfacial damage condition and porosity in the matrix, the orthotropic symmetry, bimodulus and elastic-plastic behavior are studied. The braided preform and design formulae of the 4D and 5D braided composites are also described. Numerical examples calculated by this model show that the theoretical evaluations compare well with experimental results.