SAE ARP6157

Description / Abstract: The lubricant performance capability for aero propulsion drive systems is derived from the physical properties of the oil and performance attributes associated with the chemical properties of the oil. Physical properties, such as viscosity, pressureviscosity coefficient and full-film traction coefficient are inherent properties of the lubricating fluid. Chemical attributes are critical for the formation of protective boundary lubricating films on the surfaces to prevent wear and scuffing. These attributes are also associated with surface initiated fatigue (micropitting). To assure performance and to provide required information for engineering design, methodology for at least five oil properties are being studied: (1) pressure-viscosity coefficient, (2) full-film traction coefficient, (3) scuffing resistance, (4) wear resistance; and (5) micropitting propensity. The pressure-viscosity coefficient can be measured either directly by assessing viscosity as a function of pressure using highpressure apparatus, or indirectly by measuring film thickness in an optical interferometer. This document (ARP6157) describes the test method for calculating the pressureviscosity coefficient by measuring film thickness with a WAM (Wedeven Associates Machine) and the calculating pressure-viscosity coefficient from the measured film thickness

Purpose

The purpose of this test method is to measure the elastohydrodynamic (EHD) film thickness of a test oil over a specific range of entraining velocities, five temperatures and one Hertzian contact stress. The test conditions presented here are suitable for a range of oil viscosities, including commonly used aviation oils with viscosities between 3 and 10 cSt. The measured EHD film thickness is used to calculate the pressure-viscosity coefficient at each test temperature from a commonly used Hammrock-Dowson film thickness equation [1, 2] shown in Figure 1. The pressure-viscosity coefficient is used in design, along with other physical properties of the oil, such as viscosity and traction coefficient. The five selected temperatures for measurement are common to other properties, as reported in AIR5433B [3]