Chapter 54. Lifetime Prediction Under Constant and Cyclic Loading for Ceramic Materials
- 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
Fett, T. and Munz, D. (2008) Lifetime Prediction Under Constant and Cyclic Loading for Ceramic Materials, 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.ch54
- Published Online: 28 MAR 2008
- Published Print: 1 JAN 1993
Print ISBN: 9780470375266
Online ISBN: 9780470314180
- cyclic loads;
Subcritical crack growth under static and cyclic loads in an important failure mode and is often responsible for delayed failure. The determination of subcritical crack growth data is necessary for natural flaws in order to allow lifetime predictions of real ceramic components. At least for subcritical crack extension under constant load, it is a well-known fact that the crack growth behavior of natural cracks differs significantly from that of macroscopic cracks, especially for such materials exhibiting a pronounced R-curve behavior. The influence of bridging surface interactions, responsible for R-curves in Al2O3, will be discussed with respect to strength and static lifetimes.
Moreover, failure of ceramics can also be caused due to cyclic fatigue. In cyclic tests the influence of cycles can be proved by comparing cyclic lifetimes from experiments with predictions based on static tests, or by cyclic tests with strongly different frequencies.
Experimental results obtained with both possibilities will be presented for alumina. Measured lifetimes are significantly shorter than the predictions and a reduction of lifetimes is found for increasing frequencies. From these results an effect of cycles becomes obvious and it can be concluded that a real cyclic fatigue effect occurs. The question is whether an independent effect is responsible for cyclic fatigue or whether the effect can be understood on the basis of pure subcritical crack growth as occurring in static tests.
A model for explanation of cyclic fatigue effects will be discussed that is based on the following three assumptions: The mechanisms of crack growth under cyclic load and static loading are identical.
It is assumed that the fatigue behavior in Al2O3 is a direct consequence of the R-curve effect, which is caused by crack surface interactions in the wake of cracks.
These crack surface interactions are assumed to become more and more dissolved with increasing number of cycles.