The Use of Classification Zones for Fatigue Behavior in Steels—2

Abstract

This is the second and updated version of a paper with a similar name, that was published in this journal in [1], 1977. The basic idea of classification of the Fatigue Regime is implemented again, using updated fatigue studies, and the result is a new and updated diagram. Numerous studies on Fatigue Damage and Fatigue Crack Propagation dealt with these problems either by the cumulative damage approach, or by using crack propagation equations based on linear elastic fracture mechanics. Although these two approaches are not compatible, each is useful for predicting fatigue behavior with acceptable scatter, but only within defined limits. This study updates the “Fatigue Diagram,” which classifies different combinations of stresses and crack lengths in a given specimen, as zones in which different fatigue evaluation criteria govern. The whole fatigue regime is divided into six zones, that fit to known and to new prediction methods. For the more problematic zone, where the stress amplitude is higher than the fatigue limit, and the stress intensity factor range is higher than the threshold, a superposition of two prediction procedures is shown to match closely to test results in AISI 4XXX types of steel specimens. The fatigue diagram is shown to be a useful tool for dealing with real life, fatigue design problems. The “Threshold Crack Length” is reintroduced, and directions for additional studies are indicated.