Effect of Strain-Rate and Temperature on Mechanical Response of Pure Tungsten

Abstract

This paper presents the results obtained from the investigation of the mechanical behaviour of two different batches of pure tungsten specimens. The interest in pure tungsten is due to its special properties, which has led to it finding applications in several fields, including nuclear physics. At this moment, it is used as a core material for fixed particle producing targets in several accelerator facilities around the world and it is a candidate for future ones. In these facilities, tungsten directly interacts with high energy proton beams and, consequently, is subjected to considerable deformation at high strain-rates and temperatures. From these considerations, there comes the need to properly investigate the material response under these extreme conditions. For this purpose, an ad-hoc testing campaign was performed on small dog-bone specimens in tension. The results will be applicable to the ongoing design of CERN’s AD-target as well as to other future tungsten targets operating at high power and dynamically loaded in multiple accelerator facilities. Due to tungsten’s high Ductile-to-Brittle Transition temperature, it was not possible to test it at temperatures less than 250 °C. Tests were performed at two different strain-rates (nominal value of 1 s−1 and 103 s−1) reaching a maximum temperature of 1000 °C. The dynamic tests were performed by using a Hopkinson Bar setup in the direct impact configuration. Both at low and high strain-rates, heating of the specimen was achieved using an induction coil system. A numerical inverse procedure was applied to analyse the experimental data with the aim to obtain the equivalent stress versus effective plastic strain at the different loading conditions to be used for calibration of the strength model and for the evaluation of strain-rate and thermal softening sensitivities of the material.