Effect of Temperature and Electric Field on the Damping and Stiffness Characteristics of ER Fluid Short Squeeze Film Dampers

Squeeze film dampers are novel rotor dynamic devices used to alleviate small amplitude, large force vibrations and are used in conjunction with antifriction bearings in aircraft jet engine bearings to provide external damping as these possess very little inherent damping. Electrorheological (ER) fluids are controllable fluids in which the rheological properties of the fluid, particularly viscosity, can be controlled in accordance with the requirements of the rotor dynamic system by controlling the intensity of the applied electric field and this property can be utilized in squeeze film dampers, to provide variable stiffness and damping at a particular excitation frequency. The paper investigates the effect of temperature and electric field on the apparent viscosity and dynamic (stiffness and damping characteristics) of ER fluid (suspension of diatomite in transformer oil) using the available literature. These characteristics increase with the field as the viscosity increases with the field. However, these characteristics decrease with increase in temperature and shear strain rate as the viscosity of the fluid decreases with temperature and shear strain rate. The temperature is an important parameter as the aircraft jet engine rotors are located in a zone of high temperature gradients and the damper fluid is susceptible to large variations in temperature. 1. Introduction The application of controllable fluids in engineering is an area which began to be explored in the early 1980s and fluids of interest in this study are materials that respond to an applied electric field with a remarkable change in its rheological behavior. The essential characteristic of these controllable fluids is their capability to change from a liquid state into a solid-like gel under the action of an electric field. These materials are commonly called electrorheological (ER) fluids and are normally low-viscosity colloidal suspensions. When an electric field is applied, the fluid undergoes a seemingly reversible transition to a solid in milliseconds, being able to support considerable stress under static load without yield. Willis M. Winslow (1949) was the first to discover an ER fluid and introduced the concept of controlling the apparent viscosity of an electroviscous fluid by using an electric field. ER fluids usually consist of a base fluid, usually some type of low viscosity insulating liquid, mixed with non-conductive particles (in the range of 1–10？μm diameter), such as cornstarch, gypsum and lithium salt. Since its mechanical properties can be easily controlled within a