SEDL / STP / STP1343-EB / STP15771S

A Unified Elastic-Plastic Model for Fatigue Crack Growth at Notches Including Crack Closure Effects

Dankert, M
Project engineer, Motoren-und Turbinen-Union (MTU), Friedrichshafen,

Greuling, S
Research assistant and professor, Technische Universität Darmstadt, Werkstoffmechanik, Darmstadt,

Seeger, T
Research assistant and professor, Technische Universität Darmstadt, Werkstoffmechanik, Darmstadt,

Pages: 16    Published: Jan 1999

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Abstract

The reasons for fatigue failure of many components and subassemblies are internal defects in the material or cracks and the subsequent propagation. Cracks normally originate in areas of stress concentration, e.g., at notches.

It is known that a major factor governing the service life of notched components under cyclic loading is fatigue crack growth in notches. A uniform elastic-plastic crack growth model, based on the J-integral, was developed which especially considers the crack opening and closure behavior for the determination of crack initiation and propagation lives for cracks at elliptical notches under constant or variable-amplitude loading.

For this model, an algorithm for the description of the crack opening and closure behavior and approximation formulas were developed for the determination of the stress intensity factor K and the J-integral for surface, corner and through-thickness cracks at elliptical internal and external notches. The crack growth model will be introduced and its individual modules, as well as the complete concept, were verified by experiments and two- and three-dimensional elastic and elastic-plastic finite-element analyses. Experiments, finite-element analyses, and calculations show excellent correspondence in all aspects.