Effect of a Tensile mean Stress on the Alternating Stress Required to Propagate An Edge Crack in Mild Steel
1967; Pergamon Press; Volume: 9; Issue: 3 Linguagem: Inglês
10.1243/jmes_jour_1967_009_036_02
ISSN2058-3389
Autores Tópico(s)Microstructure and Mechanical Properties of Steels
ResumoThe conditions governing growth or dormancy of fatigue cracks in mild steel subjected to the general tensile loading cycle σ m ± σ a , where σ m ≥ σ a , have been studied using plate specimens containing two small opposite co-planar edge cracks. It was found that, as in the case of zero mean load, these conditions were defined by the value of the parameter σ a 3 l; if σ a 3 l ≥ C m a crack would grow, whereas if σ a 3 l < C m it would remain dormant, where C m depended on the value of the ratio σ m /σ a . Its value at σ m /σ a = 1 corresponded to that derived from the zero mean load value by assuming that the loading cycles ± σ a and 0 to σ a were equivalent. The value of C m then decreased linearly as the ratio σ m /σ a increased to 3, after which it remained constant as σ m /σ a increased further, provided that the applied loading cycle did not result in the bulk of the specimen deforming plastically. This lower limiting value was found to correspond to that predicted from the known growth rate of a crack in mild steel, assuming that a crack cannot grow at a rate less than one atomic spacing per stress cycle.
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