RVE model with shape and position defects for predicting mechanical properties of 3D braided CVI-SiC_f/SiC composites

摘要

A representative volume element (RVE) model with internal shape and position defects for 3D braided chemical vapor infiltration (CVI) SiCf/SiC ceramic matrix composite (CMC) is developed and its mechanical properties were analyzed with finite element method. According to the characteristics of precast braiding and CVI deposition, it is assumed that the rate of deposition in each direction along the surface of the fiber bundle is similar. The SiCf/SiC-CMC samples were divided while the characteristic parameters of RVE model were measured from scanning electron microscope (SEM) images. The RVE model is established from the micro-geometric parameters. The naturally formed porous structure accurately represents the internally defective geometric shape and position. The relative errors of the calculated tensile modulus and Poisson's ratio are within 5% compared to the observed mechanical properties of material. It shows that the RVE model and simulation methods are realistic and accurate. Finally, the established RVE model is compared with randomly distributed defective RVE model for the prediction of mechanical properties. And the applicability of RVE model with shape and position defects is studied by comparison with microscopic structure of the material in SEM images.