Measurement of lubricating film thickness with thin layers of permeable hydrogels and non-permeable polyurethane under entraining action

This chapter discusses the measurement of lubricating film thickness with thin layers of permeable hydrogels and non-permeable polyurethane under entraining action. In the study described in the chapter, lubricating film thicknesses have been measured for the first time with high water content permeable hydrogels in a thin layer contact. The thickness of the fluid film in the hydrogel can be approximately predicted by modeling an equivalent elastic solid. In the study described in the chapter, for the medium and thick films produced by the entraining action where full fluid film was achieved, the permeability and water flow in the gel and the duration of loading had little effect on the film thickness. The permeability to fluid flow and water content of the gel is only important when the fluid film breaks down and the contact enters the mixed lubrication condition. Under these conditions, friction increases dramatically with the period of loading prior to sliding.