The role of fragility in EHL entrapment

Experimental measurements of time dependent film thickness in entrapped liquids, measurements of viscosity under pressure, and simulations using realistic pressure–viscosity models contribute to improved understanding of the mechanisms of entrapment formation and persistence. The ambient viscosity and pressure–viscosity coefficient affect entrapment only as much as they are predictors of behavior at much higher pressure. Fragile liquids, such as lubricating oils, experience rapid increase in sensitivity of dynamic properties to temperature and pressure as the glass transition is approached. The fragility property of lubricants appears to be of overwhelming importance to entrapment which experimental evidence indicates will reduce starting friction.