LAUSR

Abstract Tension-tension fatigue behavior of two unitized composites comprising a polymer matrix composite (PMC) and a ceramic matrix composite (CMC) co-cured together was studied at elevated temperature. The PMC parts of both unitized composites have a 2D fiber architecture and consist of the P2SI® NRPE polyimide matrix reinforced with 12 plies of carbon fibers woven in an eight harness satin weave (8HSW). The P2SI® NRPE is a high-temperature, structural thermosetting polyimide developed for 288–316 °C service temperature applications. The CMC parts of the two unitized composites consist of a zirconia-based ceramic matrix reinforced with quartz glass fibers, but have different fiber architectures. The first unitized composite includes a laminated 2D CMC reinforced with 3 plies of an 8HSW fabric. The second unitized composite includes a 3D CMC that is a single-ply non-crimp 3D orthogonal weave composite. To assess the suitability of the two unitized composites for use in aerospace components designed to contain high-temperature environments, mechanical testing was conducted under temperature conditions mimicking the service environment. In all tests, the CMC side of the test specimen was at 329 °C while the PMC side was exposed to ambient laboratory air. The tensile stress-strain behavior of the two unitized composites was investigated and the tensile properties measured for both on-axis (0/90) and off-axis (±45) fiber orientations. Tension-tension fatigue behavior was evaluated in cyclic tests performed with an R (ratio of minimum to maximum stress) of 0.05 at a frequency of 1.0 Hz. Fatigue run-out was set to 2 × 105 cycles. Both hysteresis stress-strain behavior and modulus evolution with fatigue cycles were examined for each test. The 2D-PMC/2D-CMC composite exhibited better fatigue resistance than the 2D-PMC/3D-CMC under on-axis loading, while the 2D-PMC/3D-CMC had stronger fatigue performance under off-axis loading. Specimens that achieved fatigue run-out were tested in tension to failure in order to measure the retained tensile properties. Post-test examination with optical microscopy revealed severe delamination in the laminated 2D-PMC/2D-CMC and in the PMC part of the 2D-PMC/3D-CMC. The non-crimp 3D orthogonal weave CMC part exhibited improved delamination resistance.