Specimen size effects on the flexural strength of CFCCs

Flexure tests were performed on Nicalon^TM/Al₂O₃ and Nicalon^TM/SiC composite specimens of different lengths (50 or 90 mm) and widths (2, 3 or 6 mm) under four-point bend loading at room temperature in air, and at 1,000 °C in an argon atmosphere. The specimen length did not noticeably affect the ultimate flexural strength (UFS) values of both composites. Also, an increase in the specimen width from 3 mm to 6 mm did not discernibly influence the UFS of the Nicalon^TM/Al₂O₃ specimens. However, there was a remarkable increase in the UFS of the Nicalon^TM/SiC samples when the specimen width was changed from 2 mm to 6 mm. It was apparent that the fabric architecture should be carefully considered in specimen design, such that multiple `unit cells' of the fabric are subjected to maximum tensile load during a flexure test.