Three-Dimensional Semiperiodic Line-Contact Mixed Lubrication Analysis of Functionally Graded Coated Gear Pairs

Functionally graded coatings provide an effective solution to reduce gear wear and extend fatigue life. This study models spur gear contact as a 3D axially semiperiodic problem. Frequency response functions (FRFs) are used to calculate the influence coefficients (ICs) for pressure-displacement and pressure-stress. The effect of pressure from neighboring regions is considered, and the deformation and stress distributions under surface pressure are calculated via a discrete convolution fast Fourier transformation (DC-FFT) algorithm modified by summing ICs. A mixed elastohydrodynamic lubrication model was developed using the unified Reynolds equation to simulate the behavior of gradient-coated gears during meshing. This study investigates the effects of variations in FGM coating stiffness, interface stiffness, gradient index, coating thickness, and sinusoidal rough surface on pressure distribution, oil film thickness, and subsurface von Mises stress distribution. The results provide important insights for optimizing coating designs and enhancing gear tribological performance.