High-temperature creep of a bi-directional, continuous-SiC-fiber-reinforced glass-ceramic composite

The 'off-axis', high-temperature compression creep behavior of bidirectiona lly (2D, 0/90 degrees) reinforced CAS-II/SiC (Nicalon(R) fiber) composites was studied experimentally in the stress-temperature regime of 1275-1325 de greesC and 15-50 MPa. The results indicated that the overall, high-T theolo gic response of the 2D composites was intermediate to the properties of ID composites with fiber orientations corresponding to the constituent plies i n the 2D material. This behavior strongly suggested that the 2D material be haved as an isostrain laminate during creep. A simple analysis, treating th e 2D material as a three-phase laminate, where the constituent plies were a ssigned the viscoelastic properties of the corresponding 1D materials and s eparated by thin layers of unreinforced matrix, fit the experimental data. In the case of 2D composites with the plies misoriented at 20 and 70 degree s to the applied stress (20/-70 degrees composites), however, microstructur al study suggested that growth of cracks in directions perpendicular to the applied stress due to the Poisson effect would have made a significant con tribution to the bulk strain. Hence, such crack growth acts as a limitation to the universal applicability of the laminate model. (C) 2001 Elsevier Sc ience B.V. All rights reserved.