Testing metals in tension and relaxation at elevated temperatures

Abstract

This article describes an apparatus for testing viscoplastic metallic alloys in tension at temperatures up to 400℃. Its distinctive feature is a two-shelled furnace which encompasses the test-piece. The extensometer is attached to the shoulders of the specimen and remains outside the oven, so that it works at room temperature. The strain ε_rs in the reduced section inside the tight fitting oven is calculated with the help of a finite element software from the strain ε_ext given by the extensometer. In the elastic range, the set-up was used for the measurement of Young’s moduli. In the plastic and viscoplastic ranges, it was used to draw work-hardening curves and to perform relaxation tests representative of in-service conditions. In this later case, a method to derive the strain rate sensitivity from the decrease with time of the registered stress is presented. The furnace can be easily machined in a mechanical workshop for all shapes and dimensions of test-pieces, so that it can be adapted to various studies of the workability of metallic alloys, especially those which necessitate a rapid rise and precise maintenance in temperature.