Mechanical properties of two plain-woven chemical vapor infiltrated silicon carbide-matrix composites

The elastic and inelastic properties of a chemical vapor infiltrated (CVI) SiC matrix reinforced with either plain-woven carbon fibers (C/SiC) or SIC fibers (SiC/SiC) have been investigated, It has been investigated whether t he mechanics of a plain weave can be described using the theory of a cross- ply laminate, because it enables a simple mechanics approach to the nonline ar mechanical behavior. The influences of interphase, fiber anisotropy, and porosity are included. The approach results in a reduction of the composit e system to a fiber/matrix system with an interface. The tensile behavior i s described by five damage stages. C/SiC can be modeled using one damage st age and a constant damage parameter. The tensile behavior of SiC/SiC underg oes four damage stages, Stiffness reduction due to transverse cracks in the transverse bundles is very different from cross-ply behavior. Compressive failure is initiated by interlaminar cracks between the fiber bundles. The crack path is dictated by the bundle waviness. For SiC/SiC, the compressive behavior is mostly linear to failure. C/SiC exhibits initial nonlinear beh avior because of residual crack openings, Above the point where the cracks close, the compressive behavior is linear. Global compressive failure is ch aracterized by a major crack oriented at a certain angle to the axial loadi ng. In shear, the matrix cracks orientate in the principal tensile stress d irection (i,e., 45 degrees to the fiber direction) with very high crack den sities before failure, but only SiC/SiC shows significant degradation in sh ear modulus, Hysteresis is observed during unloading/reloading sequences an d increasing permanent strain.