Deducing the Fatigue Crack Growth Rates of Natural Flaws in Silicon Nitride Ceramics: Role of R‐Curves. Issue 8 (21st May 2013)

• Record Type: Journal Article
• Authors: Härtelt, Martin; Fünfschilling, Stefan; Schwind, Thomas; Riesch‐Oppermann, Heinz; Fett, Theo; Kruzic, Jamie J.; Marshall, D. B.
• Is Part Of: Journal of the American Ceramic Society. Volume 96:Issue 8(2013)
• Page Start: 2593
• Page End: 2597
• Publication Date: 2013-05-21
• Subjects: Ceramics -- Periodicals; 620.1405
• DOI: 10.1111/jace.12410
• Languages: English
• ISSNs: 0002-7820

Abstract

<abstract abstract-type="main" id="jace12410-abs-0001"> <title> <x xml:space="preserve">Abstract</x> </title> <p>Fatigue failure is a concern when high‐strength, high‐toughness silicon nitride ceramics are used in mechanical components and the growth of natural flaws will determine the usable upper bound strength. In this study a fracture resistance curve (<italic>R</italic>‐curve) model is incorporated into an established method for deducing natural flaw growth rates from a combination of strength and fatigue life data for smooth specimens. Experimental data for a commercial silicon nitride, SL200, were examined. When compared with results deduced using a constant fracture toughness model, the new method gives more physically realistic growth rate results. Specifically, by incorporating the <italic>R</italic>‐curve the deduced fatigue threshold is equal to the reported intrinsic toughness for crack propagation of 2.2 MPa√m, whereas the constant fracture toughness model gives a physically unrealistic threshold value. Furthermore, much better agreement is achieved with the growth rates measured using macroscopic compact‐tension specimens. Overall, it is concluded that the <italic>R</italic>‐curve effect should not be ignored when deducing the fatigue crack growth rates of natural flaws in high‐toughness silicon nitride ceramics.</p> </abstract>