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在超弹性NiTi 合金室温加载、卸载的应力循环过程中,在同一样试上同时测量了应变、模量、电阻率以及内耗随应力的变化,研究了应力循环周数对上述四个参数的影响.结果表明:在增加应力至应变为4%后卸载时,试样表现了完整的超弹性,即应力卸载至零时,应变完全回复到零,这说明全部应变都是由应力诱导的可逆相变提供的.在增加应力时,电阻率单调上升并变平,模量出现极小值而内耗出现极大值;减小应力时,上述过程滞后地出现.当试验温度远高于母相转变为无公度I 相的温度T_I 时,以及试验温度低于M_f 点时,上述超弹性以及变载过程中出现的电阻、内耗及模量的变化特征均消失.将上述结果和NiTi含金在变温过程中电阻、内耗及模量的变化规律进行对比,以及对应力诱导循循环前后试样的X 光衍射分析结果均表明,上述超弹性是由于NiTi 合金中应力诱导的无公度相I/公度相C间的可逆转变所提供的.由于应力诱导I/C 转变的可逆性,因此这一转变将对NiTi 合金的双程形状记忆效应产生一定的影响.研究了应力循环周数对可逆I/C 转变的影响.
In the process of stress cycling of superelastic NiTi alloy loaded and unloaded at room temperature, the changes of strain, modulus, resistivity and internal stress with stress were measured in the same test at the same time. The influence of stress cycles on the above four parameters The results show that the specimen shows complete hyperelasticity when the stress is increased to 4% after unloading, ie the stress completely returns to zero when the stress is unloaded to zero, indicating that all the strains are caused by the stress-induced reversible phase When the stress is increased, the resistivity monotonously increases and becomes flat, the modulus appears minimum and the internal friction appears maximum, while the stress decreases, the above process lags behind.When the test temperature is much higher than the parent phase transition Is the temperature T_I of inaudible phase I and the experimental temperature is lower than M_f, the above-mentioned super-elastic and variational characteristics of resistance, internal friction and modulus occurring in the process of variability disappear.According to the above results, The changes of resistance, internal friction and modulus in the process of temperature change were compared, and the results of X-ray diffraction analysis of samples before and after stress-induced cycling showed that the above hyperelasticity was due to the stress induced in the NiTi alloy Phase I / commutation phase C. Due to the reversibility of stress-induced I / C transitions, this transition will have an impact on the two-way shape memory effect of NiTi alloys.The effect of stress cycling cycles Effect of number on reversible I / C transition.