Interlaboratory Verification of Silicon Nitride Tensile Creep Properties

• Published in: Journal of the American Ceramic Society Vol. 80; no. 4; pp. 831 - 838
• Main Authors: Luecke, William E., Wiederhorn, Sheldon M.
• Format: Journal Article
• Language: English
• Published: Westerville, Ohio American Ceramics Society 01-04-1997; Blackwell
• Subjects: Applied sciences; Building materials. Ceramics. Glasses; Ceramic industries; Chemical industry and chemicals; Exact sciences and technology; Structural ceramics; Technical ceramics; Tensile stress; Deformation; Creep; Silicon Nitrides; Mechanical properties; Durability; Round robin test; Non oxide ceramics; Structural ceramic
• ISSN: 0002-7820; 1551-2916
• DOI: 10.1111/j.1151-2916.1997.tb02911.x

Five laboratories tested NIST‐supplied, pin‐loaded, 76‐mm‐long tensile creep specimens at 1400°C under a 150 MPa load using flag‐based, laser extensometry. The laboratories reported failure time and strain and supplied the individual creep curves. Only one of the laboratories produced failure times that were significantly less than the others. It is likely that their reduced failure times resulted from small load calibration and test temperature errors. After steps were taken to ameliorate these problems, three additional tests yielded failure times that agreed with those of the other four laboratories. Although the times to failure from the four laboratories that initially agreed were statistically indistinguishable, their creep curves exhibited subtle differences. These differences probably arose because the laboratories used different gage length definitions. When we recalculated the creep curves to the same gage length definition, the differences between the four laboratories whose times to failure agreed, vanished. Although a number of the specimens exhibited edge chips, creep cracks, and obvious chemical interactions with the flags, the presence of these defects did not reduce the time or strain to failure. Two additional creep tests in our laboratory, using specimens that were grossly misaligned, yielded failure times and strains that were commensurate with those from well‐aligned specimens.