AN ANALYSIS OF THE GROWTH OF SHORT FATIGUE CRACKS

The behavior of short fatigue cracks cannot be analysed by linear elastic methods because of large scale plasticity effects as well as a breakdown in the stress intensity factor correlation of fatigue crack growth rates for crack sizes less than a millimeter in length. In the present paper a number of modifications are introduced to the linear elastic approach to establish a new parameter which is capable of correlating both long crack and short crack fatigue crack growth data. These modifications include the use of a material constant, r(e); an allowance for large scale plasticity effects; allowance for the development of crack closure; and the incorporation of the fatigue crack growth threshold. The new parameter is used with reasonable success in calculating fatigue crack growth behavior of short cracks in notched and unnotched specimens, and comparing with experimental data. In addition the analysis leads to a rationale for the dependence of the stress amplitude at the endurance level on the mean stress in a manner consistent with Gerber's parabolic relationship.