Innovative Approaches for Evaluating Interlaminar Tensile Strength of Ceramic Matrix Composites (CMCs) at Elevated Temperatures
Navy SBIR FY2008.2


Sol No.: Navy SBIR FY2008.2
Topic No.: N08-154
Topic Title: Innovative Approaches for Evaluating Interlaminar Tensile Strength of Ceramic Matrix Composites (CMCs) at Elevated Temperatures
Proposal No.: N082-154-0098
Firm: Hyper-Therm High-Temperature Composites, Inc.
18411 Gothard Street
Unit B
Huntington Beach, California 92648
Contact: Tony Magaldi
Phone: (714) 375-4085
Web Site: www.htcomposites.com
Abstract: Hot structures fabricated from CMCs are an attractive design option for specialized components of future military aerospace vehicles and propulsion systems to reduce weight and increase survivability. However, thermal-structural components fabricated from CMCs suffer from inadequate interlaminar strength, thereby increasing their vulnerability to delamination when subjected to high through-thickness thermal gradients, acoustic/high cycle fatigue, impact damage, and/or applied normal loads. Although there are Industry standards for Interlaminar Shear strength testing, no such consensus exists for Interlaminar Tension [ILT] strength testing - particularly at elevated temperatures. Better test methods are needed to characterize the interlaminar strength of CMCs to facilitate the design of efficient structures, reduce the risk of premature hardware failures, and support production Quality Assurance. Hyper-Therm HTC is proposing an innovative approach for measuring the elevated temperature ILT strength of CMCs. The test configuration directly applies an interlaminar tension force to the midplane of the laminate thereby creating a clean, ILT stress state in the specimen that does not require knowledge of the interlaminar properties in order to calculate the failure stress. Specimens can be fabricated inexpensively from flat plate stock, and because the test method does not require adhesive bonding, it can be used at temperatures up to 4000F.
Benefits: The simple specimen configuration affords the economical testing of substantial quantities for the development of a statistically significant design database as well as its' use for the tag end testing of components for production Quality Assurance. Because the test fixtures and procedure can be used at both RTA and elevated temperature test conditions, test results can be directly compared for a more meaningful assessment of environmental effects. Compatible with standard laboratory mechanical test apparatus, the fixtures and method can be adapted for elevated temperature lifing tests, such as fatigue and stress rupture, with relatively simple test setup modifications. By providing a basis for Industry consensus, the development of the proposed test method for the elevated temperature characterization of CMCs will inherently benefit both military and civilian applications for CMCs such as aero-engines.

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