Innovative Approach for Evaluating Interlaminar Tensile Strength of Ceramic Matrix Composites at Elevated Temperatures

Hot structures fabricated from ceramic composite materials are an attractive design option for components of future high-speed aircraft and propulsion systems to reduce weight and increase performance. However, available ceramic composite components fabricated from laminated fiber preforms can suffer from inadequate interlaminar tensile strength, thereby increasing their vulnerability to delamination when subjected to high thru-thickness thermal gradients, acoustic/high cycle fatigue, impact damage, and/or normal loads. The ability to intelligently design components to avoid premature interlaminar failures requires a fundamental understanding of the interlaminar properties of the material; not only at ambient temperatures, but more importantly, at elevated temperatures. Although there are Industry standards for Interlaminar Shear strength (ILS) testing of ceramic composites, no such consensus exists for Interlaminar Tension (ILT) strength testing - particularly at elevated temperatures. Under Phase I, the feasibility of an innovative test method for characterizing the elevated temperature ILT strength properties of ceramic composites was successfully demonstrated. The test method enables using small, flat material samples of representative thickness (~0.125-in) and was shown to correlate well with that obtained by flatwise tension testing of epoxy-bonded circular samples consistent with the ASTM standard (C-1468) at ambient temperature. The objective of this Phase II program is to optimize the test sample geometry and test method to suit a variety of different available ceramic composite systems (e.g., CVI, MI, PIP, etc.). This effort will culminate into the development and verification of an industry acceptable ASTM Test Standard for elevated ILT testing of ceramic composites.