Very High Cycle (VHCF) Gear Tooth Bending Fatigue in Planetary Gearsets

Seminar Speaker: Dr. Isaac Hong, Research Scientist, Department of Mechanical and Aerospace Engineering The Ohio State University

Abstract: Gear tooth bending fatigue is a catastrophic failure mode of gearboxes which occurs due to mechanical fatigue processes generated from the cyclic loading of gear teeth as they mesh. High strength alloy steels predominantly used in automotive, aerospace, and industrial applications are susceptible to fatigue crack initiation from subsurface voids or inclusions. This failure mode is distinct from surface failures associated with conventional endurance limit design and occurs at cycle counts beyond traditional test limits of 107 cycles.  The kinematic configuration at which the gear is operated defines whether the loading is reversed or released type. In a planetary gearset, for instance, sun and ring gears are subjected to released loading while planets experience reversed loading such that each gear component experiences different levels of damage.  The current gear fatigue literature lacks a fundamental understanding on tooth bending fatigue damage under different loading conditions due to absence of suitable test methods for evaluating gears for subsurface gear tooth bending fatigue failures and the different loading conditions.  A new, high efficacy rotating gear tooth bending fatigue experimental methodology is designed and validated to serve this function. Sets of experiments are performed and statistically analyzed to investigate the relative allowable stresses for equal life between the fully-reversed and fully-released load case.  Design equations for equivalent fatigue life for components of planetary gearsets are formulated and used to investigate the effects of design parameters.  At the end of this talk, several theoretical and experimental research areas are discussed along with potential funding sources.

Bio: Dr. Isaac Hong is a Research Scientist in the Gear and Power Transmission Research Laboratory (GearLab), part of the Department of Mechanical and Aerospace Engineering at The Ohio State University.  He received his Ph.D. degree in Mechanical Engineering from Ohio State in 2019.  His research interests are in the areas of gear fatigue, gear and bearing efficiency, multi-mesh deformable-body gear dynamics and issues associated with tribology, lubrication, and dynamics of ultra-high-speed system such as EV drivetrains.  He also serves on the ASME Power Transmission and Gearing Committee (PTG).