Chapter 51. Probabilistic Failure Predictions in Ceramics and Ceramic Matrix Fiber-Reinforced Composites
- 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
Lamon, J. (1993) Probabilistic Failure Predictions in Ceramics and Ceramic Matrix Fiber-Reinforced Composites, 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.ch51
- Published Online: 28 MAR 2008
- Published Print: 1 JAN 1993
Print ISBN: 9780470375266
Online ISBN: 9780470314180
Important mechanical properties for ceramic component design and lifetime predictions are dictated by the presence of preexisting microstructural defects. Ceramics contain large amounts of microstructural defects of various types, shapes, and sizes. These defects are created primarily during fabrication and surface preparation (preexistent flaws). Additional flaw populations may appear or the preexistent ones may develop in aggressive or high-temperature environments.
The presence of defects is unavoidable. Defects are still present in toughened ceramics and in composites. Therefore, approaches to reliability analysis taking into account the presence of flaw populations are important prerequisites to the design and development of reliable ceramic parts, and also devices or systems incorporating ceramic parts.
Probabilistic-statistical approaches provide the essential relationships between the three basic criteria for fracture in ceramics: fracture-inducing flaw populations, stresses, and failure probability. We can go around this triangle in any way for failure predictions.
The present paper examines failure predictions in ceramics and in ceramic matrix composites (CMCs) with a dual intent: first, to determine the influence of the flaw strength parameters upon failure probability for monolithic ceramics, and second, to propose a probabilistic approach to description of matrix damage and failure in CMCs. For the ceramics considered here, primary emphasis was placed upon the populations of fracture-inducing flaws. The flaw strength parameters, which are used to infer the failure of components, were estimated for various loading geometries in view of fracture origins identified by scanning electron microscopy. Analytical as well as computerized methods were employed for flaw strength parameters estimation. The approach proposed for prediction of failure/damage in CMCs considers the microcomposite geometry. Failures were analyzed and predicted using the Weibull model and a more fundamental model based upon the elemental strength concept. Probabilities were computed using the CERAM finite element postprocessor.
Results show that failure predictions are very sensitive to the scale factors, and that the scale factors depend strongly upon the method of estimation, the probabilistic model, and the loading geometry. The computerized approach provided the most satisfactory predictions.
Predictions of failure/damage in microcomposites are supported by experimental observations on CMCs.