The pressure-viscosity coefficient is an indispensable property in the elastohydrodynamic (EHD) lubrication of hard contacts, but often not known. A guess will easily lead to enormous errors in the film thickness. This article describes a method to deduct this coefficient by adapting the value of the pressure-viscosity coefficient until the differences between accurate film thickness approximation values and accurate film thickness measurements over a wide range of values are at a minimum. Eleven film thickness approximation formulas are compared in describing the film thickness of a test fluid with known value of the pressure-viscosity coefficient. The measurement method is based on spacer layer interferometry. It is concluded that for circular contacts the newer more versatile expressions are not better than some older approximations, which are limited to a smaller region of conditions, and that the older fits are as least as appropriate to find the pressure-viscosity coefficient of fluids, in spite of the limited data where they have been based on.

Bearing impedance vectors are introduced for plain journal bearings which define the bearing reaction force components as a function of the bearing motion. Impedance descriptions are developed directly for the approximate Ocvirk (short) and Sommerfeld (long) bearing solutions. The impedance vector magnitude and the mobility vector magnitude of Booker are shown to be reciprocals. The transformation relationships between mobilities and impedance are derived and used to define impedance vectors for a number of existing mobility vectors including the finite-length mobility vectors developed by Moes. The attractiveness and utility of the impedance-vector formulation for transient simulation work is demonstrated by numerical examples for the Ocvirk “π”, and “2π” bearing impedances and the cavitating finite-length-bearing impedance. The examples presented demonstrate both bearing and squeeze-film damper application. A direct analytic method for deriving a complete set of (analytic) stiffness and damping coefficients from impedance descriptions is developed and demonstrated for the cavitating finite-length-bearing impedances. Analytic expressions are provided for all direct and cross-coupled stiffness and damping coefficients, and compared to previously developed numerical results. These coefficients are used for stability analysis of a rotor, supported in finite-length cavitating bearings. Onset-speed-of-instability results are presented as a function of the L/D ratio for a range of bearing numbers. Damping coefficients are also presented for finite-length squeeze-film dampers.

The development of models for the elastohydrodynamic lubrication of rotary lip seals requires the measurement of the film thickness under a real seal. A new method has been developed for this purpose which is based on the use of lubricant oils in which magnetite particles are suspended (so-called magnetic fluids). A change in the fluid film thickness will create a change in the impedance of the coil of the measuring circuit, the magnetic flux of which is directed through the oil film of the contact area. The advantage of this technique is that minimal modifications have to be applied to the tribological system under examination. Initial measurements carried out with a model rubber lip seal provided new insight into the build-up of a lubricant film as a function of the rotary speed and allowed comparison with the results of a theoretical model for the analysis of lip seal lubrication developed in parallel.

In general, most analyses of radial lip seal behavior assume a static deformation state in the seal lip. Nevertheless, a dynamic excitation of the seal lip always occurs in practice, due to unroundness of the shaft or motions of the shaft center. In this first part of a two part paper the influence of dynamic excitation on the occurrence of clearances in a dry seal-shaft contact is studied, taking into account viscoelasticity and inertia of the seal material. The ultimate goal is to determine whether viscoelastic seal behavior can result in a continuous fluid film or not. First, attention is paid to the mechanical behavior of synthetic rubber under an oscillating load. The seal elastomer shows a glass transition, resulting in a strong increase in stiffness with frequency. Next, a FEM analysis of the seal-shaft contact under dynamic conditions is presented. The steady-state response of the seal is represented by a transfer function approach. It is shown that clearances develop due to viscous and inertial seal material behavior. In practice, these clearances are filled with fluid. Due to entrainment and squeeze effects a fluid film is generated. This phenomenon is designated visco-elastohydrodynamic (VEHD) lubrication, and is subject of Part 2.

This paper aims at a theoretical explanation of the following two experimental observations of radial lip seals: fluid film formation and upstream pumping action. The origins of these observations are still poorly understood. A hydrodynamic analysis is presented for the fully flooded contact zone of a smooth shaft surface running against a rough seal surface. Four roughness structures are considered: one-dimensional sinusoidal and two-dimensional sinusoidal seal roughness structures both without and with a tangential seal surface displacement. The tangential seal surface displacement is chosen asymmetric with the axial position in the contact. It follows that the tangential deformation of the one- and two-dimensional seal roughness structures used in this paper can explain the aforementioned experimental observations and simulate the observed order of magnitude of load-carrying capacity, pump rate, and friction torque found in the literature.