An ultrasonic method for lubrication film thickness measurement at elliptical contacts.

An ultrasonic effective reflection coefficient method is proposed for measuring the lubrication film thickness at the elliptical contact region. The effect of the acoustic main lobe with a larger radius is analyzed, where the superposition of the discretized reflection coefficient at both the contact region and non-contact region is considered. The coupling influences of the lubrication film shape at the non-contact region, the contact pressure distribution at the contact region and the incident acoustic pressure field on the reflection coefficient are eliminated. The proposed measurement method is validated via both simulations and experiments. The results show at small elliptical contact regions, the central film thickness in the range of 0.5 μm-5 μm can be identified accurately with the maximum measurement error of 15.9%.