Effect of a Tensile Mean Stress on the Alternating Stress Required to Propagate an Edge-Crack in Various Materials

Abstract

The conditions governing growth or dormancy of edge-cracks in plate specimens of twelve materials subjected to the general tensile loading cycle σ m ± σ a , where σ m ≥ σ a and σ m + σ a < yield stress, have been determined. 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 material and on the value of the ratio σ m /σ a . Above a certain value of σ m /σ a reached a minimum value for a given material. In general, this minimum value agreed with the value derived from the known fatigue crack growth characteristics of the material by assuming that during one loading cycle a crack will remain dormant if it cannot extend at least one atomic spacing.