Stress intensity values in conventional S-N fatigue specimens

Conference · Fri Dec 01 04:00:00 EST 1995

OSTI ID:136783

O`Donnell, T P; O`Donnell, W J ^[1]

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1. O`Donnell Consulting Engineers, Pittsburgh, PA (United States)

Existing theoretical evaluations of stress intensity. factors for cracks in cylindrical geometries have been made based on uniformly applied end tension boundary conditions, In conventional fatigue testing however, cylindrical specimens are subjected to completely reversed axial displacements. The specimens are mounted in clamping fixtures which prevent rotation of the specimen ends. For small crack depth to section diameter ratios, the assumption of a uniformly applied end tension is expected to produce reasonable estimates of crack stress intensities. However, as cracks progress through the specimen, increasing bending at the cracked section may significantly influence stress intensity values. This bending is reduced by the end constraints on the specimen. Three-dimensional finite element models have been constructed to evaluate the stress intensities associated with cracks propagating through conventional fatigue specimens. Thumbnail-shaped cracks in these specimens experience crack front straightening due to the increasing bending introduced as crack growth progresses. Such a changing crack front shape is included in the present models. Results are obtained for both uniform applied axial stress end conditions and applied end displacements. For crack depth-to-specimen diameter ratios, a/D, over one-third, the bending restraint induced in the specimens under applied displacement significantly reduce the resulting stress intensity relative to values computed for uniform end tension.

• OSTI ID: 136783
• Report Number(s): CONF-950740--; ISBN 0-7918-1344-4
• Country of Publication: United States
• Language: English

Related Subjects

42 ENGINEERING
CRACK PROPAGATION
CRACKS
EQUIPMENT
FATIGUE
MATHEMATICAL MODELS
MECHANICAL STRUCTURES
MECHANICAL TESTS
STRESS INTENSITY FACTORS
THREE-DIMENSIONAL CALCULATIONS