The effects of stress ratio on fatigue threshold

Arising from the fact that there is a reverse compression stress around a fatigue crack, it is supposed that there is an equivalent compressive high-strain area. Based upon the eigenequation of crack growth, the critical value, K_th^c, of the compressive stress intensity factor is derived. The analytical expression for the change in fatigue threshold with stress ratio is derived from the similarity between the crack closure stress intensity factor and K_th^c. The fatigue threshold values for some materials are calculated using the results of this paper; it is found that the theoretical values are in good agreement with the experimental results.