超弹性NiTi合金在应力控制循环载荷下会产生峰值应变和谷值应变的循环 累积-相变棘轮行为. 室温实验表明, 峰值应变和谷值应变的演化规 律与加载应力水平和加载波形密切相关; 同时, 在循环加载过程中, 随着 循环周次的增加, 奥氏体名义弹性模量减小, 马氏体名义弹性模量增大, 奥 氏体向马氏体转变的名义开始应力下降, 耗散能降低, 并在一定的循环次数 下趋于一个稳定值. 研究得到了一些有助于后续建立超弹性循环本构模型 的结论.
ABSTRACT: Under stressing-controlled cyclic loading, the cyclic accumulation of peak strain and valley strain, denoted as transformation ratcheting, takes place in superelastic NiTi alloy. In this work, the transformation ratcheting behavior of superelastic NiTi alloy and its dependence upon load condition were studied by experiments at room temperature. The evolution rules of peak strain, valley strain, nominal elastic modulus and transition stress under different cyclic loading cases were discussed. It is shown that the alloy presents apparent transformation ratcheting, and the value of transformation ratcheting strain and its evolution rule depend greatly upon the applied stress amplitude, mean stress and loading charts; in the meantime, the nominal elastic modulus of austenite, nominal starting stress for the transformation from austenite to martensite and dissipation energy decrease, while nominal elastic modulus of martensite increases with the increase in the number of cycles, and then reach a steady state after certain cycles. Some significant conclusions are obtained, which are useful to establish a constitutive model describing the transformation ratcheting of the material.
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