Abstract
When designing gears, the American Gear Manufacturers Association standards prescribe to carefully evaluate tooth bending fatigue, which represents one of the most common causes of gear failure. However, when cyclic loadings induce multiaxial states of stress, the analysis of the fatigue behavior of gears becomes particularly challenging and requires the employment of advanced multiaxial fatigue criteria. The goal of this paper is to evaluate the accuracy of several multiaxial fatigue criteria based on strains, when employed to predict the high-cycle fatigue life of gears. This is not how strain-based criteria are typically used. They are mainly employed to predict low-cycle fatigue lives, since they can take plasticity into account, while the high-cycle fatigue analysis is usually left to stress-based criteria. However, strain-based criteria are theoretically applicable also for high-cycle fatigue conditions. This paper aims to assess their applicability in this field. Specifically, four different criteria based on the theory of critical plane were investigated. Such type of models was chosen because not only they can estimate the level of damage, but they can also predict the direction of crack propagation right after initiation. Data of previous experimental work on AISI 9310 spur gears using the single tooth bending method to achieve crack initiation was considered. Stress and strain tensors developed during the tests were calculated through a finite element model. Subsequently, they were numerically processed employing the selected strain-based criteria. Multiple fatigue life predictions and multiple crack initiation orientations were obtained. By comparing the experimental and the numerical outcomes, it is observed that the accuracy of the tested strain-based criteria varies depending on the principle at their basis. Results show that they represent an alternative prediction tool of theoretical general applicability, which encompasses all fatigue ranges.