Abstract
The investigations have been conducted by measuring fatigue crack propagation near fatigue threshold in various structural steels differing in chemical composition and strength level. The fatigue crack propagation measurements were carried out using the constant‐load‐amplitude test in Paris‐region, R‐constant and Kmax‐constant method in near fatigue threshold region. Scanning electron microscopy at fatigue crack front on fracture surface was applied to interpret the influence of crack closure effects on the measured fatigue threshold. Marked fretting oxide deposits distributed on the fracture surface at threshold level were observed in a low load ratio resulting from the combined action of plasticity‐ and oxide‐induced crack closure under laboratory atmosphere. Fatigue threshold dependent on the load ratio appeared to be related to the extent of the crack closure effect. By considering the relationship of reversed plastic zone size and grain size the fatigue threshold in region of crack closure was calculated theoretically. The result has shown a good agreement with the experimentally measured values.
Published Version
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