Time and flow stress dependences of internal stress during stress relaxation

Stress relaxation is a potential cause of formability improvement. To describe stress relaxation, the measurement of internal stress is essential. We investigated the time and flow stress dependences of the internal stress by conducting a strain-rate-change test and stress-dip test. The comparison between the two tests revealed that the internal stress decreases as the stress relaxation progresses over time. Moreover, the internal stress decreases as the flow stress decreases. We propose that the time dependence of the internal stress could have been caused by the flow stress dependence of the internal stress because the flow stress-internal stress and the initial stress-internal stress relationships are approximately identical.