I. Reimanis—contributing editor
R Curves from Compliance and Optical Crack-Length Measurements
Article first published online: 2 APR 2010
© 2010 The American Ceramic Society
Journal of the American Ceramic Society
Volume 93, Issue 9, pages 2814–2821, September 2010
How to Cite
Fünfschilling, S., Fett, T., Oberacker, R., Hoffmann, M. J., Özcoban, H., Jelitto, H., Schneider, G. A. and Kruzic, J. J. (2010), R Curves from Compliance and Optical Crack-Length Measurements. Journal of the American Ceramic Society, 93: 2814–2821. doi: 10.1111/j.1551-2916.2010.03758.x
This work was supported by the Deutsche Forschungsgemeinschaft DFG for financing parts of this work within the SFB 483.
- Issue published online: 2 APR 2010
- Article first published online: 2 APR 2010
- Manuscript No. 27282. Received December 21, 2009; approved February 28, 2010
High-toughness, high-strength ceramics, such as self-reinforced Si3N4, derive their superior mechanical properties from microstructures that promote very steeply rising R curves. Furthermore, accurately evaluating the R curve at the earliest stages of crack growth is necessary for correctly understanding, and predicting, the mechanical behavior. Compliance- and optical-based methods for evaluating the crack length, and R curve, at the early stages of crack extension from machined notches are discussed. The earliest stages of crack growth are missed during measurements of the crack length by optical observations due to the nonuniform extension of the crack front during initial crack extension. The most accurate method of evaluating the crack length over all amounts of crack extension is from compliance measurements analyzed by solving a system of equations that incorporates both the effects of the notch and the changes in compliance with the development of bridging tractions. Such a method is computationally expensive, but for materials with steeply rising R curves, simply applying the linear-elastic compliance evaluation, which only accounts for the notch, but not the bridging tractions, gives a result within about 1%. At longer crack extensions, such an approximation method will incur significant errors; however, at this stage, optical measurements can provide accurate assessments of crack length and enable an accurate assessment of the R curve.