Finite Deformation Analysis of Pressure-Shear Plate Impact Experiments on an Elastohydrodynamic Lubricant

Pressure-shear plate impact experiments on an elastohydrodynamio lubricant (5P4E) are interpreted by means of a full finite deformation analysis of stress wave propagation in an elastic/viscoplastic material. The elastic response is modeled as that of a neo-Hookean solid, modified to include compressibility in such a way that the shock velocity increases linearly with increasing particle velocity; the viscoplastic response is modeled by means of a thermal activation model in which the activation energy is taken to be pressure dependent. The parameters in the elasticity relation are determined from the rising part of the transmitted stress profiles, which are related to transit times for multiple reverberations through the thickness of the lubricant layer. The parameters in the viscoplastic model are determined from the shear stress transmitted after nominally homogeneous states of stress are established through the thickness of the lubricant. Good agreement between measured and computed wave profiles is obtained over the entire range of pressures used in the experiments.