Fiber strength measurement for KD-I(f)/SiC composites and correlation to tensile mechanical behavior at room and elevated temperatures

Mechanical properties of KD-I-fiber-reinforced silicon carbide matrix composites were evaluated under monotonic tension at room and elevated temperatures. The measured ultimate strength showed a big decline for uncoated specimens from a room temperature value of 350 MPa, to 220 and 200 MPa at 1100 °C and 1300 °C, respectively. The decrease in ultimate strength at elevated temperatures was believed to be partly due to the oxidation embrittlement and fiber strength degradation. Specimens with anti-oxidation coatings tested at 1300 °C exhibited the ultimate strength of 320 MPa, which was comparable to that tested at room temperature. Scanning electron microscopy was employed to evaluate the in-situ KD-I fiber strengths via fracture mirror size measurements. The analysis indicated that oxidation embrittlement was the dominated damage mechanism leading to the decrease of ultimate strength. Measured values of ultimate strengths of the CMCs were compared with predictions made on the basis of in-situ fiber strength characteristics and available model.