Project: Dynamic Friction Model of Oscillatory Journal Bearing
Sponsor: Caterpillar Inc
: LSU, Mechanical Engineering
Principal Investigator: Professor Michael Khonsari
Graduate Student: Xiaobin(Mel) Lu
Contact Information: Professor Michael Khonsari

Project Description:

From astronautic robots to construction machinery, oscillation is quite common of bearing assembly motion. Complexity is introduced by the time-dependent sliding velocity. During one single oscillation cycle, the friction may vary from boundary, to mixed and then hydrodynamic lubrication regime, with the changing velocity. Hysteresis has been observed in experiments and simulated by calculations. It is a phenomenon that the friction coefficient that when the velocity increases to a specific value is different from that when the velocity decreases to that value. Nevertheless, there is not a widely acceptable dynamic friction model which covers all those three lubrication regimes so far. Also the characteristics of friction induced temperature need to be keenly investigated.

Part I: Thermal analysis
CeRom is equipped with a specially designed Tribometer made by Lewis Research Inc to measure the friction coefficient and the temperature field in oscillation of journal bearing. Figure 1 is the assembly of the oscillatory journal bearing. Figure 2 is one measurement of the friction coefficient and Figure 3 is the corresponding temperature history of four thermocouples.

Fig. 1

Fig. 2

Fig. 3

We are trying to use the experimental friction coefficient as input to simulate the temperature field of the assembly. The simulation should make good match for the four thermocouples' measurement. The temperature field in one simulation is shown in figure 4.

Fig. 4

Part II: Dynamic Friction modeling
As you can see in the friction coefficient graph, its value has dynamic characteristic in the oscillation process. Figure 5 displays this phenomenon. Please note that in this experiment, the lubricant is grease. When using oil as lubricant, this phenomenon will be expected to be more extinctive.

Fig. 5

A theoretical examination based on established model by pioneers tells us its possible mathematic description, as show in figure 6. A deeper exploration of this dynamic model is being carried on.

Fig. 6












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