As part of a cooperative research program on biaxial fatigue of the Society of Automotive Engineers (SAE), this paper reports progress to date in the evaluation of methods for predicting fatigue life of a round-bar specimen (1045 steel) with a shoulder fillet, subjected to fully reversed bending, torsion and combined bending and torsion, inphase and 90° out of phase.

First, test data from the literature on multiaxial fatigue behavior of notched specimens are reviewed. Factors influencing that behavior (for example, notch stress state and type of notch geometry) are discussed, as are approaches for correlating the data.

Next, a number of different methods for predicting life to “crack initiation” (millimetre sized cracks) are compared with test data for the SAE specimen. The methods are: (a) elastically calculated notch maximum shear and octahedral shear stress criteria based on nominal stresses and fatigue notch factors, (b) maximum shear and octahedral shear strain criteria, (c) a cyclic plastic work approach, and (d) a criterion based on amplitudes of maximum shear strain and of normal strain on the plane of maximum shear. Methods (b) through (d) utilize measured notch strains. Advantages and shortcomings of the methods are discussed.

Measured notch bending and torsional shear strains are compared to values estimated by simplified elastic-plastic analyses which investigate both use of Neuber's rule and the assumption of total strain invariance (that is, notch strain concentration factor equal to an elastic stress concentration factor.)