Fatigue cracks initiate at microstructural defects.
Lebensdauervorhersage verbessern Rissentstehung und Kurzrisswachstum unter Schwingbeanspruchung
Michael Vormwald
ABSTRACT The micro crack density de-pends on the material itself as well as on the strain level. Defect size, shape, and po-sition with respect to the surface and to neighboring cracks are decisive whether or not it may cause failure. New lifetime prediction techniques try to improve accuracy by simulating this stochastic process. The microstructure has a significant influence on crack growth in the early stage. This effect can be taken into account either by incorporating experimental findings in empirical crack growth laws or by mapping the inhomogeneities into an adequate mechanical model. Using such models, the endur-ance limit of a macroscopically crack free component can be explained with a frac-ture mechanics based approach. However, elastic plastic fracture mechanics must be applied. Crack tip opening displacement and J-integral are commonly used as crack driving force parameters. Additionally, crack closure has to be considered which sig-nificantly differs from the behaviour of long cracks .
Publication Source: Materialprüfung, ISSN: 0025-5300
Issue: 2003-3, pp 92-99
Publisher: Carl Hanser Verlag München
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