循环加载条件下TiNi形状记忆合金棒材的超弹性行为

Superelastic Behavior under Cyclic Loading for TiNi Shape Memory Alloy Bars

通过TiNi形状记忆合金棒材在准静态循环加载条件下的力学性能实验,以相变应力、变形模量、残余应变、耗能能力等作为该合金棒材的超弹性特征参数,分析了这些特征参数随循环次数的变化规律。结果表明:循环初期,各参数的值随循环次数的增加显著降低,到一定次数(εmax=5%时,约10次;εmax=2%时,约15次)后,这些参数的值趋于稳定。即最初只具有部分超弹性的TiNi形状记忆合金棒材,经过一定次数的循环"训练",可呈现出明显的完全超弹性,从而使得合金的力学性能趋于稳定。工程应用时,应考虑循环加载对合金超弹性能的影响,根据具体工况合理设计。

The mechanical properties of TiNi shape memory alloy bar were investigated using loading-unloading cycling tests under quasi-static conditions. The Phase transformation stress, deformation module, residual strain, dissipated energy and so on are considered as superelastic characteristic parameters of these specimens. The changes of these parameters with cyclic number were analyzed. Results indicate that at the beginning stage of loading cycling, these parameters considerably decrease with the increase of cyclic loading number. After certain cyclic numbers （as Еmax=5%, the number of cyclic loading may approximately be 10; as Еmax=2%, the number of cyclic loading may approximately be 15）, the value of these parameters tends to be steady. In other words, after loading-unloading cycling ＂ training＂, the initially pseudoelatic TiNi shape memory alloy bar can obviously present complete superelasticity, thus, the mechanical property parameters of this alloy tend to be steady. In order to apply this alloy bars to practice, the influence of cyclic loading on alloy superelasticity should be considered, and the appropriate design should be proposed based on practical condition.