A finite-element-aided ultrasonic method for measuring central oil-film thickness in a roller-raceway tribo-pair

Abstract

Roller bearings support heavy loads by riding on an ultra-thin oil film (between the roller and raceway), the thickness of which is critical as it reflects the lubrication performance. Ultrasonic interfacial reflection, which facilitates the non-destructive measurement of oil-film thickness, has been widely studied. However, insufficient spatial resolution around the rolling line contact zone remains a barrier despite the use of miniature piezoelectric transducers. In this study, a finite-element-aided method is utilized to simulate wave propagation through a three-layered structure of roller-oil-raceway under elastohydrodynamic lubrication (EHL) with nonlinear characteristics of the i) deformed curvature of the cylindrical roller and ii) nonuniform distribution of the fluid bulk modulus along the circumference of the oil layer being considered. A load and speed-dependent look-up table is then developed to establish an accurate relationship between the overall reflection coefficient (directly measured by an embedded ultrasonic transducer) and objective variable of the central oil-film thickness. The proposed finite-element-aided method is verified experimentally in a roller-raceway test rig with the ultrasonically measured oil-film thickness corresponding to the values calculated using the EHL theory.

A comprehensive review of non-destructive methods for bearing lubricating oil film thickness measurement

“…When the sensor resolution is insufficient to support accurate measurement of the oil film thickness distribution around the contact area, finite element methods can assist in oil film thickness measurement with greater accuracy than results obtained from single ultrasonic wave measurements (Dou et al. , 2022a, 2022b, 2022c, 2022d).…”

“…However, the contact area width of roller bearings is smaller than the sensor width, requiring a ray model to calibrate the sound reflection coefficients (Zhang et al, 2015a(Zhang et al, , 2015b. When the sensor resolution is insufficient to support accurate measurement of the oil film thickness distribution around the contact area, finite element methods can assist in oil film thickness measurement with greater accuracy than results obtained from single ultrasonic wave measurements (Dou et al, 2022a(Dou et al, , 2022b(Dou et al, , 2022c(Dou et al, , 2022d.…”

“…Coatings, serving as protective layers for bearings, may cause attenuation or resonance phenomena in incident sound waves depending on their thickness (Dou et al, 2022a(Dou et al, , 2022b(Dou et al, , 2022c(Dou et al, , 2022dFu et al, 2022). Under conditions requiring highprecision measurements, the influence of the reflected sound waves cannot be overlooked.…”

“…The phase shift model solves the frequency blind spot problem between the two models (Dou et al, 2022a(Dou et al, , 2022b(Dou et al, , 2022c(Dou et al, , 2022d. When there are significant variations in oil film thickness, both the spring and resonance models exhibit low measurement accuracy.…”

“…Coatings are regarded as thin multilayer structures, and their interference with measurements can be eliminated by determining the acoustic impedance of the coating (Beamish et al, 2022). Establishing a four-layer ultrasonic coating model allows for accurate measurement of oil film thickness (Dou et al, 2022a(Dou et al, , 2022b(Dou et al, , 2022c(Dou et al, , 2022d.…”