Critical review of criteria for notch sensitivity in fatigue of metals

It was the purpose of this report to summarize and to appraise critically the numerous interpretations and correlating methods that have been proposed in the technical literature to compare the endurance limits for notched rotating beam fatigue specimens with those of unnotched specimens. The interrelation of the ideas proposed by several investigators were also studied. After surveying all relevant hypotheses it was summarized that notch-sensitivity of a metal member depends upon three different factors, namely: (a) the basic material characteristics, of which the local work-hardening (or strain strengthening) capacity may be considered as an index; (b) degree of material homogeneity, which is influenced by inherent defects , tensile residual stresses, heat treatments etc.; (c) geometry of the specimen, (including over-all size); the radius at the root of notch is of prime importance in this geometric factor. It was concluded that the criterion for fatigue failure and for endurance limit should include not only the stress value at the critical point as is conventionally assumed, but also the conditions existing in a critical region or volume surrounding the point. A rational approach and procedure for attacking the problem of notch effect as well as size effect is suggested.Office of Naval Research, U. S. Navy, Contract N6-ori-71, Task Order IV; Project NR-031-00