Modeling and numerical simulation of the mechanical behavior of woven SiC/SiC regarding a three-dimensional unit cell

Abstract

The mechanical behavior of a two-dimensional woven SiC/SiC ceramic matrix composite (CMC) under tensile loading is modeled by regarding a three-dimensional unit cell of the composite which takes the waveness of the fiber yarns in two directions into account. The numerical evaluation of the model is accomplished by means of the finite element method (FEM). Because of the small diameter (15 μm) of the fibers in the bundles, these fibers are not considered as single entities in the finite element mesh. Instead the mesh is constructed on the yarn scale considering the fiber bundles as homogeneous with `fiber bundle' properties. The brittle cracking of interyarn matrix as well as transverse cracking of the fiber bundles are considered by defining a fracture criterion for these components. The increasing degradation of the fiber bundles in fiber direction during progressive loading is described by three damage variables. Damage and cracks are modeled by reducing the elastic coefficients of the finite elements. The scattering of the strength values of the single components is regarded by using Weibull distribution. Before mechanical loading, the structure is subjected to thermal loading to consider the residual thermal stresses in the structure resulting from the cooling down process after fabrication of the composite. The effect of the scattering of the strength values on the behavior of the unit cell will be examined.