SIMPLE METHODOLOGY FOR CALCULATING THE CONSTANTS OF GAROFALO EQUATION

Abstract

The examination of the high temperature plastic properties of metallic materials was realised by the torsion plastometer SETARAM or by the compression plastometer DIL805A/D. The brass CuZn30 was used as the test material. Peak stress detection was performed for two independent variables, temperature and velocity of deformation. The set experimental plan forms the test array 54, i.e. five temperatures 650, 700, 750, 800, 850 °C and four strain rates of 0.5, 2.5, 12.5 and 25 s-1. It was necessary to evaluate measured data and to determine the mathematical model of the peak stress. For this aim, the Garofalo equation was used. This equation contains 4 material constants. The currently method used to determine the material constants takes a relatively long time and requires a number of auxiliary calculations. In this method, nonlinear regression is often used, which requires the initial estimation of parameters. The article presents a mathematical analysis and a simple methodology for calculating the material constants of the Garofalo equation. A general linear regression is used for the calculation that does not require an initial estimate of the material constants. The numerical calculation of material constants is
documented on the measured peak stress data.