Chapter 41. Monotonic and Cyclic Rupture of a Silicon Nitride Ceramic
- John B. Wachtman Jr.
Published Online: 28 MAR 2008
Copyright © 1993 The American Ceramic Society
Proceedings of the 17th Annual Conference on Composites and Advanced Ceramic Materials, Part 1 of 2: Ceramic Engineering and Science Proceedings, Volume 14, Issue 7/8
How to Cite
Hild, F. and Marquis, D. (1993) Monotonic and Cyclic Rupture of a Silicon Nitride Ceramic, in Proceedings of the 17th Annual Conference on Composites and Advanced Ceramic Materials, Part 1 of 2: Ceramic Engineering and Science Proceedings, Volume 14, Issue 7/8 (ed J. B. Wachtman), John Wiley & Sons, Inc., Hoboken, NJ, USA. doi: 10.1002/9780470314180.ch41
- Published Online: 28 MAR 2008
- Published Print: 1 JAN 1993
Print ISBN: 9780470375266
Online ISBN: 9780470314180
- tensile tests;
- ductile materials;
- SEM observations;
- monotonic bend tests
A testing system has been designed to perform tensile tests on brittle materials. Whereas this test is very easy to perform on ductile materials, it is much more complicated for brittle materials, because the failure strains are very small (typically of the order of 0.1%). Therefore, if no particular precaution is taken, spurious bending strains induced by the testing grips can easily reach values of the order of magnitude of the tensile strains.
Tensile tests under monotonic and cyclic loading conditions were carried out on a silicon nitride ceramic (Si3N4: SN 220M, Kyocera, Kyoto, Japan; density of 3200 kg/m3). A scatter in failure strength or in number of cycles to failure is observed. This scatter is related to the initiation defects through SEM observations. In all cases, initial defects in the material turned out to be the main cause leading to the failure by fracture of the specimens. The monotonic tensile tests are compared to three different kinds of monotonic bend tests, i.e., three-point bend test, four-point bend test, and disk bend test performed on the same material. A stress heterogeneity effect is observed on the strength when the four series of tests are compared. A size effect analysis is performed and shows that a Weibull-type modeling is not satisfactory.
Based on the experimental work, an expression of the failure probability is proposed. The failure probability is related to the initial defect distribution through a weakest-link assumption and through an independence of events hypothesis. A correlation with a Weibull law is derived. By comparing experiments and predictions, it can be concluded that the flaw distribution is different in the four sets of experiments.
An extension to cyclic loadings is proposed on the basis of a Paris law. This extension shows that a unified expression of the failure probability can be derived to integrate both monotonic and cyclic loadings. The experimental data are analyzed within the previous framework and show that the stable propagation stage does not lead to a significant increase of the flaw size.