镍钛形状记忆合金塑性屈服后力学行为研究

Investigation on Post-yielding Behavior of Ni-Ti Shape Memory Alloy

为研究形状记忆合金(SMA)塑性屈服后力学行为的变化规律,在室温下将塑性屈服处理及未处理的SMA试样进行加卸载循环试验,对比分析了应变速率、应变幅值及循环次数等加载工况对SMA的相变应力、耗能能力及残余应变等力学参数的影响规律,给出了SMA塑性屈服后各力学性能与加载工况的关系.结果表明:受塑性屈服效应影响,SMA的滞回曲线无明显相变平台,并在卸载时出现较大残余应变.与超弹性SMA相比,塑性屈服后SMA在相同应变幅值下耗能能力下降超过40%,峰值应力增加约90%.塑性屈服效应不影响SMA极限应力,但对其极限应变有减弱作用.在结构振动控制所用的SMA耗能装置中,部分塑性应变有利于提高其自恢复能力,但在强震大变形作用下,需考虑因塑性屈服应变而造成的超弹性损失及残余应变的增加.

In order to investigate the post-yielding mechanical behaviors of SMA, the tension loading-unloa- ding tests were performed on the post-yielding samples and superelastic samples at room temperature. Numbers of cycles, strain amplitudes and strain rates were considered to investigate their effects on the mechanical properties. The relationship between mechanical parameter and its corresponding loading factor was proposed. The experimental results show that these post-yielding stress-strain curves of SMA display no obvious superelastic plateau and have significantly residual strains after unloading completely. Compared to superelastie SMA, dissipated energy per unit volume of post-yielding SMA decreases more than 40% and the peak stress increases about 90 %. Plastic-yielding strain has not much influence on ultimate stress while it has a strong influence on ultimate strain. It can be concluded that a small amount of plastic strain is helpful to obtain high recentering force of SMA-based devices. Superelastic degradation and obvious residu- al strain of post-yielding SMA should be considered in the SMA-based devices＇ design.