Tensile creep and stress relaxation tests were performed simultaneously.
Then, the tensile creep was converted into the tensile stress relaxation by Ozawa's and Wittmann's methods.
The converted stress relaxation was agree with the measured at loaded ages 3, 7days, but different at 14, 28 days.
On the other hand, it was found that Wittmann's method was easily availaue in comparison with the other methods.
The converted stress relaxation by Wittmann's method was used in simple thermal stress analysis.