A critical assessment of high-temperature dynamic mechanical testing of metals

Determination of the mechanical properties of materials under the combined effects of high-temperatures and high strain-rates has been all important and challenging issue. A strategy has been proposed and evaluated recently towards this purpose in which a heating cell with accurate temperature control is synchronized with the split Hopkinson pressure bar (SHPB) system. This strategy allows pre-heating the specimen to desired temperatures before arrival of the stress wave and provides all experimental technique for the measurement of dynamic mechanical properties of materials at high-temperatures. Since its advent, this method has gained increasing interest in the Community of dynamic mechanical testing owing to its case of manipulation. However, a Couple Of Critical problems should be addressed to validate the experimental results. Among the problems, a crucial one is associated with the temperature change in the heated specimen upon its contact with the relatively cold bars. In this paper, experiments were designed to determine the influence of cold-contact-time (CCT) on the temperature variation within the specimen. The experiments were conducted oil Ti700 alloy at strain-rates of similar to 10(4) s(-1) and at temperatures from 20 to 800 degrees C. The results show that the CCT does have a strong effect on the experimental results. Based on the experimental results and our analyses, we believe that the data call faithfully reflect the material behavior if CCT is shorter than 50 ins. While in most systems without the heating cell being synchronized with the SHPB system, the typical CCT is about 500 ms, and therefore the experimental data cannot be taken as representing the material behavior (C) 2008 Elsevier Ltd. All rights reserved.