Surface Instabilities in Linear Orthotropic Half-Spaces With a Frictional Interface

This paper studies the friction induced vibrations that may develop in the neighborhood of steady sliding states of elastic orthotropic half-spaces compressed against a rigid plane moving tangentially with a prescribed speed. These vibrations may lead to flutter instability associated to a surfacelike oscillation. The system of dynamic differential equations and boundary conditions that governs the small plane oscillations of the half-space about the steady sliding state is established. The general form of the surface solutions to the plane strain case is given. The way how the coefficient of friction varies with changes in some of the system’s parameters is investigated. It is shown that for certain combinations of material data, low coefficients of friction are found for surface flutter instability (lower than in the isotropic case).

Hydrodynamic Lubrication in Simple Stretch Forming Processes

Theoretical models for the hydrodynamic lubrication of plane strain and axisymmetric sheet metal stretch forming processes with cylindrical and spherical headed punches, respectively, are developed. The lubricant is treated as an isoviscous Newtonian liquid for both geometries. In addition, the influence of sheet heating due to plastic deformation with an exponential variation of viscosity with temperature is analyzed for the plane strain case.