An equivalent uniaxial stress process for fatigue life estimation of mechanical components under multiaxial stress conditions

Fatigue life estimation of mechanical components under multiaxial state of stress has an important role in design virtual phases. Moreover the virtual simulation of components and structures may be efficient only if it uses reliable and quick tools in each step of the analysis. Especially the requirement of minimum computational effort must be guaranteed by the analytical instruments in fatigue damage evaluation starting from simulated stresses. In this context the authors believe the uniaxial equivalent stress is the only approach useful at this purpose, because multiaxial criteria have extremely large computational times. However the uniaxial equivalent process is not accepted by the largest part of the researchers for the reason that a definition in agreement with experimental results it has not been founded yet. Furthermore some theoretical problems appear related on the generalization of the static concept of equivalent stress to dynamic conditions. In this paper the authors introduce an original form of equivalent uniaxial process starting from an accurate theoretical analysis about octahedral planes. It will be demonstrated that this process can be defined both in time-domain and in frequency-domain. Then the good agreement between experimental tests found in literature and the expectations of the proposed method will be shown also by a comparison with the most excellent multiaxial criteria