In this work, a numerical model is proposed to evaluate the fatigue life of power train components, whose metal material is essentially behaved as being inhomogeneous due to a thin and hard surface layer on the top of the relatively soft base material. As a typical case in the power train of automobiles, a key component in a vibration-filtration device between the engine and gearbox is subject to the inertial load arising from angular velocities as well as the torque loads, varying cyclically with time in a form of variable-amplitudes in the field of fatigue. The strain or stress responses to the inertial loads are not only due to the distributed mass of this component alone, but also due to the contact imparted from the neighboring components (e.g., massive coil springs). As the loads have caused the component to exceed the yield somewhere in the metal structure, strain-life approaches are employed to compute the number of cycles. As usual, the rain-flow counting is utilized to uncover each individual constant-amplitude stress-strain loop, upon which both Morrow and Smith-Topper-Watson formula are applied to account for the mean stress effect. A commonly-used linear damage cumulative summation, known as Miner’s rule, is applied to assess the fatigue damage fraction. Through the results from the fatigue simulation, it will be demonstrated that it is the inner core that will be more damaged than the case-hardened surface in the case that the fatigue cycle is not very short. The author will address the issue how to convert any complicated loads, which usually consume tremendous time in the fatigue test, into simple loads, on the basis that they are equivalent in the ultimate fatigue damage fraction. This will have the practical significance for decelerated durability test. Furthermore, how the depth of case-hardening affects the fatigue life will also be shown in this study.
|Poster Session||00:00-00:00||Zane Yang|
71 – A numerical simulation methodology for steel plates with inhomogeneous properties at variable-amplitude loads