Measurement of flow stress in hot axisymmetric compression tests

Abstract

This paper describes good practice for the measurement of hot flow stress in metallic materials. It is applicable to hot (isothermal) uniaxial axisymmetric compression tests at medium to high rates of strain (10⁻⁴–10² s⁻¹) at deformation temperatures below the solidus.

Guidance is provided on appropriate testpiece geometries and methods of verifying the temperature distribution along the length of the testpiece. Flow diagrams are given showing all the steps that are necessary, including the correction factors that need to be applied for deformational heating and for the determination of true stress. Details are given of the calibration procedures that should be followed to provide traceability to the National Measurement System.

Technical input to the document has been provided by a steering group containing academic researchers and representatives of industrial users and producers of a wide range of engineering materials. An experimental and modelling programme on an aluminium alloy, AA5052; on 316 stainless steel and a nickel alloy, Nimonic 901, over a range of temperatures and strain rates has been conducted during the preparation of the document to underpin the procedures in the guide.

Keywords:

• flow stress
• hot axisymmetric compression tests