Hot rheology tests

Overview

ABSTRACT

Although a significant number of hot deformation processes are identified, conducted with specifically developed systems, no standard has been enacted as of yet. These systems consist in three different natures, according to the deformation process aimed at by the test: compression, tension and hot torsion. The aim of compression and torsion is to study the rheology of the heated material whereas traction is generally linked to environmental aspects. These tests allow for the characterization of the sensitiveness of a material to the deformation speed or to the temperature and the determination of the apparent activation energy as well as the work-hardening and dynamic restoration parameters.

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AUTHORS

Frank MONTHEILLET: Civil mining engineer and Doctor of Science - Research Director, CNRS
Christophe DESRAYAUD: Master assistant

INTRODUCTION

There are a large number of hot characterization methods, carried out using specially developed fixtures, but no standard has ever been issued. Such a standard does exist, however, for the cold mechanical strength test (ASTM standard).

There are three main types of test: compression, traction and hot torsion. Compression and torsion are designed to study the rheology of the material when hot, while traction is generally reserved for damage-related aspects.

This article does not go into detail on SPD (Severe Plastic Deformation) specific devices such as Equal Channel Angular Extrusion (ECAE), Accumulative Roll Bonding (ARB) or High Pressure Torsion (HPT), which allow access to high levels of deformation, but do not directly provide information on material rheology (flow stress). Moreover, these devices have only been developed anecdotally at high temperatures.