Techniques for Smooth Specimen Simulation of the Fatigue Behavior of Notched Members

The initiation of fatigue cracks in a notched member is determined by the local cyclic stress and strain at the notch root. A relationship, proposed by Neuber, is used to relate the notch root stress-strain response to the nominal stress in the notched member. Further, several methods based on Neuber's rule allow a smooth cylindrical specimen to be used to simulate the stress-strain behavior of the notch root metal. The fatigue life of the smooth specimen is shown to furnish a satisfactory estimate of the fatigue life of the notched member, and the stress-strain plot of the smooth specimen is useful in understanding the local effects on the notch root metal of various nominal load histories. Results are reported for notched specimens subjected to variable load histories and for the corresponding smooth specimen simulations for 2024-T4 and 7075-T6 aluminum, aircraft quality 4340 steel, and Ti-8Al-1Mo-1V.