The Temperature Dependence of the Divergence Pressure

The so-called controversy in elastohydrodynamic lubrication (EHL) regarding the nature of the shear dependence of viscosity, Eyring versus Carreau, is truly a controversy regarding the pressure and temperature dependence of the low-shear viscosity. The Roelands hoax became acceptable in EHL because ignoring the universal previtreous piezoviscous response made the traction calculated with the Eyring assumption appear to be reasonable. Traction and minimum film thickness calculations sometimes require the description of viscosity at pressures up to the glass transition pressure. There have been few measurements of viscosity at pressures up to the glass pressure. Therefore, a need exists for a piezoviscous model that extrapolates accurately and the Hybrid model fills that need. Here, an improved relation for the temperature dependence of the divergence pressure is offered and extrapolation is demonstrated for a polyalphaolefin.