eJournals International Colloquium Tribology 23/1

International Colloquium Tribology
ict
expert verlag Tübingen
125
2022
231

Application of the Non-linear Behaviour of Longitudinal Ultrasonic Waves in Lubricants Monitoring

125
2022
S. Taghizadeh
R. S. Dwyer-Joyce
ict2310351
23rd International Colloquium Tribology - January 2022 351 Application of the Non-linear Behaviour of Longitudinal Ultrasonic Waves in Lubricants Monitoring S. Taghizadeh Leonardo Centre for Tribology, Department of Mechanical Engineering, University of Sheffield, Mappin Street, Sheffield S1 3JD, UK Corresponding author: staghizadeh1@sheffield.ac.uk R.S. Dwyer-Joyce Leonardo Centre for Tribology, Department of Mechanical Engineering, University of Sheffield, Mappin Street, Sheffield S1 3JD, UK The performance of lubricants directly effects the energy efficiency and level of environmental pollution. Oxidation due to high operating temperature, wear particles and contamination by fuel are factors that degrade lubricants and reduce their functionality. There are several techniques to determine the state of degradation such as infrared spectroscopy or chemical constituent examination. One of the limitations of these methods is being offline measurement and so an oil sample is required to be measured in a laboratory environment. Non-destructive methods using ultrasound have been widely used in tribology to detect contact and measure oil film thickness. In this method, longitudinal or shear ultrasonic waves are emitted by piezoelements. Ultrasonic waves propagate in a medium and are reflected at boundaries between a solid-lubricant or solid-air contact. The amplitude of the reflected or transmitted signal is decreased which contains information about the interface. Usually, ultrasonic waves are low power and elastic and the interface response is linear. However, when a high-amplitude ultrasonic waved is propagated in a linear or non-linear medium, or incident at an imperfect contact, the reflected or transmitted wave is distorted, and higher harmonics are generated. Some studies [1-4] showed the relevance of higher harmonics to the third order elastic constant in solids and pressure-density relationship in fluids. In the present work, the authors used a finite-amplitude method to measure the non-linear ultrasonic behaviour of a lubricant and related this to degradation. In this approach, high-power longitudinal waves propagate in the lubricant. The amplitude of fundamental frequency and second order harmonics were captured by the second transducer (receiver). A non-linear ultrasonic coefficient is then measured [1,2,5]: (1) where k is wavenumber, x distance between transducers (emitter and receiver), A 1 and A 2 are the amplitude of the fundamental frequency and 2 nd order harmonic. Eq. 1 can be represented considering only the amplitude of fundamental frequency and second harmonic [5]: (2) Four samples of lubricant were examined: fresh and degraded diesel engine oil Cat Deo 10W-30, fresh PAO 40 and fresh PAO 100. Table 1 shows the density and dynamic viscosity (measured using a rheometer TA Instruments Rheometer HR10) of the lubricants. Table 1: Density and dynamic viscosity of the lubricants. Lubricant Density (g/ m 3 ) Dynamic Viscosity (Pa. s) at Temperature 25 Degraded Cat Deo 10W-30 0.86 0.122 Fresh Cat Deo 10W-30 0.86 0.146 Fresh PAO 40 0.85 0.765 Fresh PAO 100 0.85 2.92 Fig. 1 compares the variation of nonlinear coefficient β′ with the distance between the transducers. The distance between the transducers is classified as near field and far field. In the near field, β′ is less sensitive to the variation of density and viscosity of the lubricants. For example, although the viscosity of degraded and fresh Cat Deo 10W-30 are varied, β′ cannot distinguish the difference. However, it was observed in the far field (specifically at the distance longer than twice the near field), β′ is clearly dependent on the viscosity of the lubricant. As the viscosity of the lubricant decreases, β′ increases. However, 352 23rd International Colloquium Tribology - January 2022 Application of the Non-linear Behaviour of Longitudinal Ultrasonic Waves in Lubricants Monitoring their densities are quite similar, and a densitometer hardly can measure the difference. This method has the potential to be used in the on-line measurement of degradation of the lubricants. Figure 1: Variation of β′ of the lubricats with the distance. References [1] A. Hikata, B.B. Chick, C. Elbaum, Dislocation contribution to the second harmonic generation of ultrasonic waves, J. Appl. Phys. 36 (1965) 229-236. https: / / doi.org/ 10.1063/ 1.1713881. [2] K.E. Van Den Abeele, Elastic pulsed wave propagation in media with secondor higher-order nonlinearity. Part I. Theoretical framework, J. Acoust. Soc. Am. 99 (1996) 3334-3345. https: / / doi.org/ 10.1121/ 1.414890. [3] R.T. Beyer, Parameter of Nonlinearity in Fluids, J. Acoust. Soc. Am. 32 (1960) 719-721. https: / / doi. org/ 10.1121/ 1.1908195. [4] R.T. Beyer, The parameter B/ A, in: M.F. Hamilton, D.T. Blackstock (Eds.), Nonlinear Acoustics, Academic Press, 1998. [5] C. Pantea, C.F. Osterhoudt, D.N. Sinha, Determination of acoustical nonlinear parameter β of water using the finite amplitude method, Ultrasonics. 53 (2013) 1012-1019. https: / / doi.org/ 10.1016/ j.ultras.2013.01.008.