An Analytical Study of the Fatigue Notch Size Effect
by
P. K. Mazumder
Department of Metallurgy and Mining Engineering
and
F. V. Lawrence, Jr.
Professor of Civil Engineering and Metallurgy
Abstract
An analytical expression for Kf in terms of notch depth (A), elastic stress concentration factor (Kt) and initiated crack length (aI) has been developed. Together with the strain-controlled fatigue concepts and the Newman’s stress intensity correction factor solution, the expression for Kf was used to study the notch-size effect and other phenomena related to the notch-size effect.
Results of this study indicate that the notched specimen behavior was best represented by Peterson’s equation rather than Neuber’s equation. The material constant (a) based on Peterson’s equation for steels and aluminum alloys, was related to the stain-controlled fatigue properties and the fatigue crack propagation parameters.
Conditions for which nonpropagating fatigue cracks will form was studied using the present model. The analytical expression for Kf was used to evaluate the length of the nonpropagating cracks as a function of the stress level. A universal plot based on the theories developed for notched specimens is proposed that well describes the behavior of cracked specimens. The intrinsic crack length (lo) proposed by Haddad et al, could be related to the material constant (a).
Analytical estimates were compared with the experimental results taken from the literature and a good agreement was observed.
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