Interlaminar Mode I and Mode II Fracture Toughnesses in Ceramic Matrix Composites (CMCs)

Interlaminar Mode I and Mode II Fracture Toughnesses in Ceramic Matrix Composites (CMCs)
Navy STTR FY2013.A

Sol No.:	Navy STTR FY2013.A
Topic No.:	N13A-T008
Topic Title:	Interlaminar Mode I and Mode II Fracture Toughnesses in Ceramic Matrix Composites (CMCs)
Proposal No.:	N13A-008-0258
Firm:	Weidlinger Associates, Inc. 40 Wall Street 18th Floor New York, New York 10005-1304
Contact:	Marcus Rutner
Phone:	(212) 367-2951
Web Site:	http://www.wai.com
Abstract:	Susceptibility to delamination is one of the major weaknesses of ceramic matrix composites (CMCs). Knowledge of the resistance of composite to interlaminar fracture is essential for life cycle prediction analyses of structural components. The current test method for Mode I-interlaminar fracture toughness, the double cantilevered beam (DCB), is not satisfactory for thin CMC specimens because the compliance of the cantilever arms yields a spurious energy release rate. For Mode II-interlaminar fracture toughness testing, the end notched flexure (ENF) test is the most popular, but this test is not a standardized test method as yet. CMC components are in heavy demand for parts subjected to high heat. However, elevated temperature creates more severe conditions for interlaminar fracture toughness testing. A need exists, therefore, for reliable Mode I- and Mode II-interlaminar fracture toughness test methods which are applicable to a wide range of CMC materials, allowing for quantification of Mode I and Mode II-fracture toughness and accounting for the effects due to complexity of ply architecture at room temperature and elevated temperature up to 1316C (2400F). We propose several alternative methods, and a means to evaluate them using finite element analysis and actual testing. We will refine and downselect the methods to standardize an efficient, accurate testing approach.
Benefits:	The test concepts for interlaminar Mode I- and Mode II- fracture toughness measurement offer the following benefits: 1. The test concepts are simple, isolate one dominant failure mode and allow reliable testing 2. The test concepts are applicable to all classes of ceramic matrix composites. 3. The test concepts allow for uniaxial and two-directional fabrics 4. The test concepts allow for measuring complex architecture 5. The test concepts allow testing at room temperature as well as at elevated temperature up to 1315C (2400F).

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