Measurement of True Stress-True Strain Curve up to Large Strain Extent at Elevated Temperature in Ti-6Al-4V Alloy with Image Analysis Tensile Test Method

Abstract

The image analysis tensile test method was applied to obtain true stress-true strain curves at elevated temperature in Ti-6Al-4V alloy. A CCD camera successfully captured the profile change of a specimen during the tensile test. Minimum radius and neck curvature can be calculated from the profile, then used to determine true strain and true stress after necking using Bridgman’s equation. True stress-true strain curves up to a strain of 0.8 were obtained in the high temperature tensile test at 850 ℃. The true stress-true strain curves show work hardening at a strain rate of 0.2 s-1 and dynamic restoration at a strain rate of 0.01 s-1 in the tensile test at 850 ℃. On the other hand, in compression tests, the true stress-true strain curves show steep decrease in true stress after yielding. This might be due to the effect of barreling of the specimen, rather than any metallurgical structural change. The image analysis tensile test method is applicable to obtain accurate high-temperature true stress-true strain curves at elevated temperature up to large strain extent.