A collaborative research team from Xi'an Jiaotong University and Imperial College London has developed a coupled elastohydrodynamic–acoustic framework for high-resolution ultrasonic measurement of dynamic film thickness in lubricated rolling bearing contacts. The study, published in Engineering, provides a noninvasive method for evaluating central oil film thickness—a parameter critical to the efficiency and reliability of rolling bearings in large rotating machinery.
The Challenge
Lubricant film thickness directly influences bearing performance, yet accurate in-situ measurement remains exceptionally difficult. Dynamic fluctuations, elastic deformation, cavitation, and varying oil supply all complicate real-world readings.
Traditional optical and electrical methods require transparent components or strict electromagnetic shielding, which severely limits their industrial application. While ultrasonic techniques offer a promising path for non-destructive testing, they have been hampered by limited spatial resolution and complex interface reflections.
Methodology: Bridging Simulation and Acoustics
The researchers tackled these limitations by combining two advanced modeling approaches:
1. Elastohydrodynamic Lubrication (EHL) Simulations
- Employed the Elrod–Adams algorithm with JFO boundary conditions to accurately account for cavitation.
- Generated surface deformation profiles, pressure distributions, and cavitation regions.
2. High-Fidelity Acoustic Modeling
- Built using COMSOL Multiphysics to analyze how inlet/outlet zone lengths, rotational speed, and load affect ultrasonic wave propagation and reflection.
Key signal finding: The reflection coefficient distribution showed a symmetric double-peak with a central valley pattern. Cavitation shifted this central valley toward the inlet and raised the reflection coefficient; changes in speed and load further modified the signal.
The team established a six-step procedure to extract central film thickness. They introduced a correction factor linking the overall sensor reflection coefficient to the central region value, using polynomial fitting to relate the factor to operating parameters. The corrected reflection coefficient was then converted to film thickness via the spring model.
Validation Experiments
The framework was tested under two configurations:
- Glass–oil–steel setups: Fluorescence measurements confirmed the predicted reflection coefficient distribution trends.
- Steel–oil–steel (all-steel) bearings: Measured film thickness closely matched theoretical EHL predictions, with a maximum error of just 12.7% —significantly outperforming conventional ray and spring models.
Significance & Future Work
- What makes this approach unique: It accounts for real contact geometry, elastic deformation, and cavitation effects—factors previous methods ignored.
- Practical advantage: The method supports in-situ, noninvasive monitoring and is compatible with piezoelectric ceramic sensors attached directly to bearing surfaces.
- What's next: The research team plans to extend the approach to other bearing types and develop dimensionless formulations to broaden applicability.
The study provides a powerful tool for condition assessment and life prediction of rolling bearings in industrial rotating equipment. By enabling accurate, real-time film thickness measurements without disrupting machinery, this framework could significantly improve maintenance strategies and operational reliability.
The paper "A Coupled Elastohydrodynamic–Acoustic Framework for High-Resolution Ultrasonic Measurement of Dynamic Film Thickness in Lubricated Contacts" is authored by Pan Dou, Yayu Li, Suhaib Ardah, Tonghai Wu, Min Yu, Thomas Reddyhoff, Yaguo Lei, and Daniele Dini. Full text available at: https://doi.org/10.1016/j.eng.2026.01.014