3D Measurements of Lubricant and Surface Temperatures Within an Elastohydrodynamic Contact

Abstract

We present an infrared microscopy technique, capable of measuring the temperature of both the bounding surfaces and the oil film in an elastohydrodynamic contact. This technique can, for the first time, spatially resolve the oil film temperature in three dimensions. The contact is produced by loading a steel ball against a sapphire disc, and the film is viewed using an infrared microscope focussing through the disc. Two band pass filters are used to isolate the radiation from the oil film, and Planck's law is applied to data obtained at a known temperature as part of the calibration procedure. The proposed technique requires the emissivity of the oil film to be measured, which is acquired in situ and is shown to vary strongly as a function of thickness and temperature. The technique is validated under pure rolling conditions, when the temperature of the oil film is equal to the controlled lubricant reservoir temperature, and also compared to an equation commonly used to predict average film temperatures, confirming the value of the unknown constant. The technique is then used to gain insights into the thermal/rheological behaviour within a contact. This is important since the temperature of elastohydrodynamic contacts is critical in determining friction and hence the efficiency of machine components and this technique enables much needed validation and provides input data for CFD and numerical simulations.

Shear heating, flow, and friction of confined molecular fluids at high pressure

“…Interestingly, a b value of 9 was also used to fit recent experimental ∆T f versusγ results for DCMP under EHL conditions. 10 In these current simulations, b is larger for DCMP compared to PAO and increases with increasing P for both fluids. This suggests that the flow for DCMP deviates more from the commonly assumed Couette case and that higher P leads to larger deviations for both fluids; this will be further investigated in Section 3.2.…”

“…[60][61][62][63] Fluid film T rise is also common in tribology experiments under EHL conditions. [7][8][9][10] In recent NEMD simulations, Langevin thermostats 59 with a range of coupling times (0.5-50 ps) were tested to reproduce the experimental thermal conductivity of α-Fe surfaces. 64 In the current simulations, the Langevin thermostat in the bottom slab was assigned a coupling time of 0.1 ps, by which a thermal conductiv-ity similar to α-Fe surfaces (as a model for steel) was simulated.…”

“…5 The denominator on the right hand side of eqn (3), b, can vary broadly between 4 and 24. 10 A value of 8 implies that heat is generated evenly through the fluid film (i.e. Couette flow) while a value of 4 suggests that all of the heat is generated at the mid-plane.…”

CFD modeling compared to temperature and friction measurements of an EHL line contact

“…It should be noted that the technique has recently been refined to enable the temperature of the oil film itself to be measured three-dimensionally [9]. However this advanced technique has not been used in the current study, since the aim was only to compare surface temperatures with those predicted from CFD.…”

On the Temperature and Lubricant Film Thickness Distribution in EHL Contacts with Arbitrary Entrainment

“…Further insight into the problem has been made possible by the development of temperature mapping using infrared microscopy based on the approach developed by Ausherman et al [19]. IR technique was applied by Spikes et al [20,21] and further improved by Reddyhoff et al [22,23], Le Rouznic et al [24], and Lu et al [25]. Yagi, Nakahara et al [26][27][28] used infrared microscopy for temperature mapping of the contact under high sliding conditions where the dimple occurs.…”