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Improved Fatigue Life Evaluation Methods for LWR Components

“Improved Fatigue Life Evaluation Methods for LWR Components” W. J. O’Donnell, D. P. Jones, J. S. Abel, J. S. Porowski, E. J. Hampton, and M. L. Badlani, report prepared for Division of Engineering Technology, Office of Nuclear Regulatory Research, March 1987.

Keywords: elastic-plastic crack growth; plastic cycling; fatigue testing; A533B pressure vessel steel; J-integral theory; environmental effects; crack initiation

The applicability of a general elastic-plastic crack growth analysis method is established herein for a wide range of geometries and loading conditions including the extensive plastic cycling encountered in most fatigue testing. Data on A533B pressure vessel steel is used because extensive test results are available for various geometries and for elastic, local-plastic and grossly plastic loading conditions.

The method, based on J-integral theory, is then applied to include reactor water crack propagation rates per Section XI of the ASME code in the S-N fatigue curves for A533B. These environmental effects are found to be far greater than were anticipated when constructing the existing fatigue design curve in the ASME Code. The next step in the development of improved fatigue life evaluation curves is to include environmental effects on crack initiation. Much of the available reactor water environmental data was obtained on notched specimens where local strains were well beyond yield.

Cyclic inelastic finite element analyses are needed to obtain the local strain ranges that existed in these tests. The results will make it possible to use this data in developing improved S-N fatigue life curves which include reactor water effects on crack initiation. The methods described herein are also applicable to other LWR ferritic and austenitic materials and can be used to evaluate the effects of acceptable weld imperfections and residual stresses on the fatigue life of weldments. The approach used herein also provides a means of incorporating future crack initiation and crack growth research data into fatigue life evaluation curves, while maintaining existing Regulatory and ASME Code safety margins.