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对镍钛形状记忆合金在-20~120℃的温度区间内进行了应变控制下的循环加/卸载实验研究。实验结果表明,在温度低于80℃时,相变应力和耗散能均随循环周次的增加而迅速降低,残余应变随循环周次的增加而增加,它们均在一定的循环周次后均趋于稳定值；一旦温度超过80℃,逆相变开始应力随循环周次的增加反而增加,向前相变开始应力和逆相变结束应力与温度的线性关系不再保持。温度低于奥氏体完成温度之前,初始为马氏体相或马氏体-奥氏体混合相,残余应变随温度增加而减小,耗散能随着温度的增加而增加；温度高于奥氏体完成温度时,初始为奥氏体相,残余应变随温度的增加而增加,耗散能随温度的增加而下降,二者分别在40和20℃达到最小值和最大值。

Within the temperature range of -20-120 ℃,the cyclic transformation characteristics of NiTi SMA were investigated in this work under the strain-controlled cyclic loading conditions.Experimental results show that,when the test temperature was lower than 80 ℃,the transformation stresses and dissipation energy de-cease rapidly with the increasing number of cycles and reach to their stable values after certain cycles.However, when the test temperature was higher than 80 ℃,the start stress of reverse transformation (i.e.,from induced martensite to austenite phase)increases during the cyclic loading,and then the start stress of forward transfor-mation (i.e.,from induced martensite to austenite phase)and finish stress of reverse transformation do not in-crease linearly with the temperature any more.When the test temperature was lower than the austenite finish temperature,the initial phase of the alloy consists of the martensite or the mixed martensite and austenite,the residual strain and dissipation energy decrease and increase with an increasing temperature,respectively;how-ever,once the test temperature was higher than the austenite finish temperature,the initial phase of the alloy was pure austenite,the residual strain and dissipation energy increase and decrease with an increasing tempera-ture,respectively.The minimum and maximum values of them were observed at 40 and 20 ℃,respectively.