An Approach to Account for Negative R-Ratio Effects in Fatigue Crack Growth Calculations for Pressure Vessels Based on Crack Closure Concepts

[+] Author and Article Information
J. M. Bloom

Structural Mechanics Section, Babcock & Wilcox Company, Research and Development Division, Alliance, OH 44601

J. Pressure Vessel Technol 116(1), 30-35 (Feb 01, 1994) (6 pages) doi:10.1115/1.2929555 History: Received November 04, 1992; Revised September 14, 1993; Online June 17, 2008


Current fatigue crack growth procedures in the commercial nuclear industry do not clearly specify how compressive loads are to be handled and, therefore, regulatory agencies usually recommend a conservative approach requiring full consideration of the loads. This paper demonstrates that a more realistic approach to account for compressive loads can be formulated using crack closure concepts. Several empirical plasticity-induced crack closure models were evaluated. An approach in the Section XI ASME Code for tensile loading only has been extended and evaluated for negative R -ratios. However, the paper shows this approach to be overly conservative. The approaches using crack closure models are shown to be more accurate. An analytically based crack closure model, while more complicated, is shown to give a theoretical basis to the empirically derived crack closure models. The paper concludes with a recommendation for modifying the current ASME Code practices consistent with the crack closure models and fatigue crack growth data from negative R -ratio tests.

Copyright © 1994 by The American Society of Mechanical Engineers
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