RESPONSE OF SIC-COATED CARBON CARBON COMPOSITES TO TENSILE LOADING ATAMBIENT AND ELEVATED-TEMPERATURES - AN EXPERIMENTAL AND FINITE-ELEMENT STUDY/

Response of SiC-coated carbon/carbon composites has been investigated under tensile loading at various temperatures. Elevated-temperature te sts have been carried out in an inert atmosphere to eliminate the effe ct of oxidation on the strength of the laminate. Extensive post-failur e analyses by scanning electron microscopy (SEM) and optical microscop y (OM) have been performed to reveal the failure mechanisms. A shift i n the failure mechanisms with the rise in test temperatures has been o bserved. This change in failure modes was found to be responsible for increase in strength at 1093 degrees C (2000 degrees F). Ultrasonic C- scanning has shown excessive delamination at room temperatures, while complete fiber-bundle failure with minimum delamination was identified as the final failure event at elevated temperatures. Analyses of the stress/strain behavior and an investigation of the damage growth at va rious temperatures are presented. Ultrasonic C-scans of fractured spec imens have been performed, and the growth of delamination at ambient a nd elevated temperatures is discussed. Isoparametric layered shell ele ments developed on the basis of the first-order shear deformation theo ry have been used to model the thin laminates of C/C under tensile loa ding. Both large deformations and plastic strain behavior have been co nsidered in the finite element analysis to account for the non-lineari ties encountered during the actual test. Finite element results are pr esented to corroborate the experimental findings, and a comparison in respect to displacement and stress/strain behavior is given to check t he accuracy of the finite element analysis. Reasonably good correlatio n between the experimental and finite element results has been establi shed.