A new algorithm for estimating fatigue life under mean value of stress

This paper discusses two problems: allowing for mean value of torsional stress and the variability of material properties with out of-parallel fatigue characteristics. The effect of normal mean stress and shear mean stress is modified by reduction coefficients, which, to a large extent, depend on the value of existing loads. These coefficients have been developed experimentally on the basis of an analysis of the findings from fatigue tests on 2017A-T4 and 6082-T6 aluminium alloys and S355 alloy steel. The methods of calculation, suggested in this paper, are applicable to the materials in elastic-plastic state. The suggested algorithm for estimating fatigue life for the combination of bending or tension and compression and torsion under shear stress is based on Kluger's stress criterion. The usability of the algorithm was verified by comparing the calculation results with the results of own experimental tests on 2017A-T4 and 6082-T6 aluminium alloys, which have been noted to indicate sensitivity to shear mean stress, and the tests found in the professional literature ( tests on S355, 30CrNiMo8 and 30NCD16 steel and Ti-6Al-4V titanium alloy). A comparative analysis of the calculation and experimental results proved that there is a satisfactory correlation between them.