Abstract NiTi shape memory alloys (SMAs) exhibit distinct thermo-mechanical behaviors affected by the loading frequency, ambient conditions, and the specimen geometry. The effects of these factors are essentially due to the competition of different timescales in phase transitions of NiTi SMAs. However, quantifying the timescale competition still remains a challenge for SMAs subjected to force- or displacement-controlled cyclic loadings. Here we present a thermo-mechanically coupled model for one-dimensional SMA bars to address the effects of timescale competition on the thermo-mechanical responses. Scaling the model gives a dimensionless number λ indicating the ratio of the loading time to the characteristic time of heat transfer (affected by ambient conditions and the specimen geometry). The model shows that it is the timescale ratio λ that dictates the thermo-mechanical responses. Comparison of simulation results with experimental data validates the coupled model and the effects of the timescale ratio λ on the thermo-mechanical responses. The coupled model can predict the responses of SMAs under different combinations of external loadings and ambient conditions and thus provide guidelines for experimental design.

中文翻译：

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时间尺度竞争决定了 NiTi 形状记忆合金棒的热机械响应

摘要 NiTi 形状记忆合金 (SMA) 表现出不同的热机械行为，受加载频率、环境条件和试样几何形状的影响。这些因素的影响主要是由于 NiTi SMA 相变的不同时间尺度的竞争。然而，量化时间尺度竞争对于承受力或位移控制的循环载荷的 SMA 来说仍然是一个挑战。在这里，我们提出了一个一维 SMA 条的热机械耦合模型，以解决时间尺度竞争对热机械响应的影响。缩放模型给出一个无量纲数 λ，表示加载时间与热传递特征时间的比率（受环境条件和试样几何形状的影响）。该模型表明，时标比率 λ 决定了热机械响应。仿真结果与实验数据的比较验证了耦合模型和时间尺度比 λ 对热机械响应的影响。耦合模型可以预测 SMA 在外部载荷和环境条件的不同组合下的响应，从而为实验设计提供指导。