Rate-dependent response of superelastic Cu-Al-Mn alloy rods to tensile cyclic loads

We report the results of tensile cyclic loading tests conducted to examine the dependence of constitutive relations for superelastic Cu-Al-Mn alloy rods on loading rates. Recently, Cu-Al-Mn alloy rods with diameters up to 8mm have been developed by the authors, and it has been demonstrated that these rods have excellent superelastic strains of more than 8%, which is comparable to NiTi alloys and far superior to other Cu-based alloys. No information is available, however, on the rate dependence of constitutive relations for Cu-Al-Mn alloys. In this study, we prepare two Cu-Al-Mn alloy rod specimens, whose lengths and diameters are 150mm and 8mm, respectively. Their stressstrain relations are examined under the loading frequencies of 0.001, 0.5, and 1Hz with constant strain amplitude of 4.5%. It was found from the tests that the maximum stress increase in Cu-Al-Mn alloys due to higher loading rate was less than 5%. Thermo-mechanical analysis predicts that stress increase in Cu-Al-Mn alloys is about 1/4 of that in NiTi alloys, which agrees reasonably well with the experimental observations. Such low stress increase is highly desirable in the design of seismic devices such as dampers and isolators.