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A round robin study of mechanical test methods provided an opportunity for direct comparison of flexural and tensile test methods and results for one hundred ninety test specimens (one hundred flexure and ninety tension) of a commercial ceramic fiberreinforced ceramic matrix composite (Sylramic™ S-200) consisting of eight plies of ceramic grade (CG)-Nicalon™ eight harness satin weave (8HSW) fabric in a silicon-carbonitride matrix (Sylramic™) with a boron-nitride-containing interphase coating. Flexural test specimens (110 × 9 × 3 mm) were tested in four-point quarter-point loading per ASTM Test Method for Flexural Properties of Continuous Fiber-Reinforced Advanced Ceramic Composites (C 1341). Grand means for the ultimate “flexural strength,” flexural strain at ultimate “flexural strength,” and elastic modulus in flexure for the ten laboratories, were 339 MPa, 4640 μm/m and 93 GPa, respectively. The dog-bone tensile test specimens (150 × 12 × 3 mm) were tested per ASTM Test Method for Monotonic Tensile Strength Testing of Continuous Fiber-Reinforced Advanced Ceramics with Solid Rectangular Cross-section Specimens at Ambient Temperatures (C 1275). Grand means for ultimate tensile strength, strain at ultimate tensile strength, and elastic modulus for the nine laboratories were 251 MPa, 4310 μm/m and 93 GPa, respectively. A key finding was that the ultimate flexural strength values calculated from the conventional beam bending equations are not representative of the measured ultimate tensile strength. The key material variable was the tensile strength of the coated ceramic fibers, rather than fiber volume fraction, bulk density, or open porosity. Dimensional measurements was a key experimental variable.
continuous-fiber reinforced ceramic composite, advanced ceramic, tension testing, flexure testing, Nicalon,™ Sylramic™
Research director, Gateway Materials Technology, Mt. Prospect, IL
Associate professor, University of Washington, Seattle, WA