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

The mechanical behavior of a two-dimensional woven SiC/SiC ceramic matrix c omposite (CMC) under tensile loading is modeled by regarding a three-dimens ional unit cell of the composite which takes the waveness of the fiber yarn s in two directions into account. The numerical evaluation of the model is accomplished by means of the finite element method (FEM). Because of the sm all diameter (15 mum) of the fibers in the bundles, these fibers are not co nsidered 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 a s well as transverse cracking of the fiber bundles are considered by defini ng a fracture criterion for these components. The increasing degradation of the fiber bundles in fiber direction during progressive loading is describ ed by three damage variables. Damage and cracks are modeled by reducing the elastic coefficients of the finite elements. The scattering of the strengt h 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 t he cooling down process after fabrication of the composite. The effect of t he scattering of the strength values on the behavior of the unit cell will be examined. (C) 2000 Elsevier Science B.V. All rights reserved.