On the significance of crack tip shielding in fatigue threshold - Theoretical relations and experimental implications

被引:3
作者
Schindler, HJ [1 ]
机构
[1] EMPA, Swiss Fed Labs Mat Testing & Res, CH-8600 Dubendorf, Switzerland
来源
FATIGUE CRACK GROWTH THRESHOLDS, ENDURANCE LIMITS, AND DESIGN | 2000年 / 1372卷
关键词
crack tip shielding; crack closure; intrinsic threshold; experimental; residual stress; influence functions; cut compliance method; threshold chart; R-effect;
D O I
10.1520/STP13425S
中图分类号
T [工业技术];
学科分类号
08 ;
摘要
The fatigue crack growth (FCG) threshold behavior of elastic-plastic materials is analyzed theoretically by simplistic mechanical considerations. Emphasis was laid upon two of the key aspects of threshold, which are both still controversially discussed in the literature. intrinsic threshold and extrinsic crack tip shielding. The analytical relations derived from the model confirm experimental indications, that at R-ratios beyond a certain limit FCG and its threshold is governed by intrinsic mechanisms, whereas at rower R it is crucially influenced by extrinsic shielding mechanisms. The latter are postulated to consist of a crack-closure and a non-closure part, which is confirmed by preliminary experimental data as well as data from the literature. To measure crack closure independently, a new experimental technique, the so-called cut compliance method, is proposed, which is shown by some preliminary tests to work well even in the threshold regime. The model and the derived mathematical relations also enable one to distinguish between those parts of the threshold that are inherently associated with FCG, and the ones that are geometry- or load-history-dependent. Therewith conservatively transferable threshold data can be obtained.
引用
收藏
页码:46 / 62
页数:17
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