Minimum Circumscribed Ellipse (MCE) and Stress Scale Factor (SSF) criteria for multiaxial fatigue life assessment

• Fatigue life assessment of notched specimens is presented.
• MCE and SSF criteria results have good fatigue life correlations.
• For the selected loading paths the MCE and SSF have similar results.
• The SFF criterion was upgraded to account with the bending stress gradient.
• The MCE and SSF criteria were validated with a third party fatigue data.

Many fatigue models proposed in literature are validated by the author’s data and usually they are not corroborated with other author’s lab work. In this paper, two multiaxial fatigue criteria, the Minimum Circumscribed Ellipse (MCE) and the Stress Scale Factor (SSF), are used to assess fatigue life under multiaxial loading conditions. Two different sets of fatigue data obtained from two different steels and from two different research groups were used in order to evaluate the accuracy of the models MCE and SSF regarding multiaxial fatigue life assessment. The fatigue data used here have two major features: stress concentrations, always present in mechanical components, and the loading path effects, with the inherent changing on the principal stress directions and/or the variation of the stress amplitude ratio (tau/sigma). Furthermore, different failure criteria were adopted for each material and different testing setup. For the Ck45 material, the failure criterion was the crack initiation, for the C40 material was the total rupture. Another factor to point out is that the Ck45 fatigue results were obtained under bending/torsion conditions and the C40 fatigue results were achieved in axial/torsion loading conditions. Results show good correlation between experiments and fatigue life estimations. Some remarks and conclusions concerning the performance of the MCE and SSF models are presented.