Forced oscillations dynamic tribometer with real-time insights of lubricated interfaces

Abstract

This paper presents an innovative forced oscillations dynamic tribometer, the CHRONOS tribometer, with a lubricated ball-on-flat contact configuration fitted out with an in situ optical visualization system and a triggered high-speed camera. The CHRONOS tribometer generates controlled oscillating kinematics by means of a shaker with a range of strokes from 5 µm to 2.5 mm and an oscillation frequency which can be adjusted from 5 Hz to 250 Hz. Displacement and velocity are measured using a vibrometer. The ball-on-flat mean contact pressure is set between 200 MPa and 600 MPa. During motion, the instantaneous normal and friction forces and the interfacial film thickness distribution (in the nanometer scale) are simultaneously measured. In addition to this instantaneous approach, a more macroscopic approach is developed in terms of moving averages of friction and velocity. Another parameter, the friction-velocity tilt angle, is also introduced. This last parameter may give information on the friction-velocity dependence. Eventually, the experiments performed on the CHRONOS device lead to the representation of synchronized temporal signals of displacement/velocity, friction, and lubricant central film thickness. This superimposition of key parameters reveals time effects introduced by the periodical fluid squeeze and flow in the contact. Published by AIP Publishing.

Frictional Response of Lubricant in EHL Contact under Transient Bi-directional Shear Loading

“…The total friction was given by the contributions of sub-contact areas of different film thicknesses. Also, the formation of friction loops and the squeeze action were observed for high frequencies and long stroke lengths [25].…”

Transient effects of squeeze and starvation in an EHL contact under forced oscillation: On the film-forming capability

“…The experiments were performed using a forced oscillations tribometer CHRONOS described in [21]. The contact is in ball-on-flat configuration using a fixed steel ball with a diameter of 25.4 mm and a quartz moving flat counterpart.…”

“…• Observations were performed using a speed camera with a frame size of 1600 × 500 pixel 2 , a resolution of 1.6 μm/pixel and a frame rate of 1000 fps. This camera is associated with a lens allowing interferometric measurements [21].…”

“…It is worth noting that all these works concerns fully-flooded contacts. However when lubricated contacts are submitted to reciprocating motions, the oilsupply conditions may change during time: for instance, the contact becomes transitorily starved at the position where the direction of the displacement changes (see figure 8 in [21]). The starvation phenomena are referred in the literature only under steady-state kinematics either experimentally [22][23][24][25] or numerically [26][27][28].…”

Tribolumen: A Tribometer for A Correlation Between AE Signals and Observation of Tribological Process in Real-Time—Application to A Dry Steel/Glass Reciprocating Sliding Contact

“…Furthermore, this spectrogram shows that the harmonics were very clear and distinct and did not show any great disturbance or interference with horizontal modes. In other words, the device vibration modes did not interfere with the measured signal of friction, which implies that the device had an appropriate stiffness avoiding any vibrational disturbance in the contact [36]. signal of friction, which implies that the device had an appropriate stiffness avoiding any vibrational disturbance in the contact [36].…”