Determining Worst-Case Fatigue Thresholds Grain-Bridging Ceramics.

Kruzic, J. J. ; Yuan, R. ; Cannon, R. M. ; Ritchie, R. O.

Technical Information Center Oak Ridge Tennessee

关键词: Fatigue thresholds;    Ceramics;    Crack-growth properties;    Procedures;    Cracks;   

RP-ID  :  DE2003805154

学科分类：工程和技术（综合）

美国|英语

来源: National Technical Reports Library

【 摘 要 】

A method for determining worst-case cyclic fatigue thresholds in grain-bridging ceramics by quantifying the role of bridging is demonstrated for a model alumina. Crack-growth properties for both long and short (less than 2 mm) cracks emanating from machined notches were investigated. When compared as a function of the applied stress-intensity range (DeltaK), growth rates (da/dN) were far higher and fatigue thresholds DeltaKTH were markedly lower with short cracks, with growth being observable at the lowest driving forces for short cracks emanating from razor micronotches. For growth rates less than 10 times minus 8th power m/cycle, da/dN vs. DeltaK data for short cracks merged with the steady-state data for long cracks after approximately 2 mm of extension. This value corresponds well to the measured crack-bridging zone length for long fatigue cracks grown near DeltaKTH. The crack-tip shielding contribution due to bridging was quantified using multi-cutting compliance and crack-opening profile techniques.