Considerations on the Necessity of Determining Principal Stresses and Directions for Analysis of Material Durability under Multiaxial Fatigue

摘要

A special situation arises when multiaxial fatigue loadings are present, given not only the time-dependency of extreme principal stress values, but also the fact that principal plane positions change during one load cycle (non-proportional loading). Thus, the analysis of principal stress and principal direction variation becomes a very important step, necessary to be carried out before starting any multiaxial fatigue testing. Based on the above, the authors present a generalized method for computing principal stresses and determining principal plane positions, applicable for cyclic tension-torsion loadings with zero mean stresses but with different phase-shifts and amplitude ratios. Based on original experimental data and data collected from the literature, the authors point out in the final part of the paper that the maximum shear stress can be considered as the main parameter for plotting Wohler curves.