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Fatigue crack propagation near fatigue threshold in various structural steels
Author(s) -
Han Seungho,
Reinhold Patrick,
Ring Markus,
Dahl Winfried
Publication year - 1996
Publication title -
steel research
Language(s) - English
Resource type - Journals
eISSN - 1869-344X
pISSN - 0177-4832
DOI - 10.1002/srin.199605535
Subject(s) - materials science , crack closure , fretting , fracture mechanics , fatigue limit , fracture (geology) , amplitude , oxide , plasticity , composite material , structural engineering , metallurgy , optics , physics , engineering
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 K max ‐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.