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_a³l; if σ_a³l < C_m a crack would grow whereas if σ_a³l < 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.