Fragility and the dynamic crossover in lubricants

The property of fragility in glass forming liquids is introduced to elastohydrodynamic lubrication (EHL). Using viscosity measurements for three liquids that have been the subject of traction studies the fragility of liquids is shown to be important to EHL traction and the property that most influences the representative (Eyring) stress. The derivative Stickel analysis is then carried out for lubricants. Using viscosity measurements, the dynamic crossover is detected for the first time in lubricants. The viscosity at the crossover is either constant or varies slowly with temperature and pressure and the crossover pressure varies with temperature in a manner similar to the glass transition pressure. The free-volume model fails to predict the occurrence of the dynamic crossover.