超弹性NiTi记忆合金螺栓紧固件自松弛创成机理研究

The accumulation of the unrecoverable deformation at the screw root due to the transformation ratcheting can be thought as the important factor for the loss of the super elasticity and the self-loosening of smart memory alloy (SMA) bolt. In order to maintain the good performance of SMA bolt in the engineering application, this project aims to break through the technical limitations of the traditional studies for the bolt loosening based on the elastic-plastic ratcheting, and plans to research the self-loosening of NiTi shape memory alloy bolt by considering both the single factor effect of the transformation ratcheting and the coupling influences of the ratcheting, the creep and the self-rotation of the nut. The self-loosening simulation of bolt are undertaken by considering the constitutive model of the transformation ratcheting, the coupling constitutive model of both the transformation ratcheting and the creep for NiTi shape memory alloy, and the coupling model based on the three kinds of factors. The experiment for the mechanic characters about the NiTi shape memory alloy is carried out to obtain the necessary parameters for simulation. The loss rule of the super elasticity and the self-loosening rule of the NiTi shape memory alloy bolt are disclosed in this research by considering the effects of temperature, the preload of bolt and the alternate loading model. The constructed knowledge system has the capability of directing the reliability design of the NiTi shape memory alloy bolt joint, and has important significance and broad prospects in the fields of aerospace, and protecting against and mitigating earthquake disasters.

形状记忆合金（SMA）螺栓由于相变棘轮效应导致螺纹根部应力集中区域不可恢复变形的累积是其超弹性丧失及自松弛的重要诱因。为了维护SMA螺栓的工程使用价值，本项目拟突破传统的螺栓弹塑性棘轮效应自松弛研究的技术局限，围绕相变棘轮效应单因素作用，及棘轮效应、蠕变、螺母自旋多因素耦合作用下的超弹性NiTi记忆合金螺栓自松弛问题展开研究。构建NiTi记忆合金相变棘轮效应本构模型、棘轮效应与蠕变耦合作用本构模型，求解一致性切线模量，构建多因素耦合数值模型进行螺栓自松弛仿真。开展NiTi记忆合金力学性能实验，获取所需的仿真参数。搭建螺栓自松弛实验平台，对仿真结果进行验证，观察螺栓相变及弹塑性区域对自松弛的影响。考虑温度、预紧力及交变载荷模式因素的影响，揭示NiTi螺栓超弹性丧失及自松弛规律。所构建的知识体系不仅可指导NiTi记忆合金螺栓可靠性设计，在航空航天、防震减灾等领域将具有重要意义和广泛前景。

形状记忆合金(SMA)螺栓联接以其独特的超弹性，在土木工程等特殊场合的减振吸能与被动控制方面具有无可比拟的优势，而材料棘轮效应与蠕变的耦合作用导致SMA螺栓联接的服役性能恶化。因此，亟需研究SMA螺栓联接材料服役的性能衰退机理，进一步提升其工程应用价值。本项目以具有功能结构一体化特征的SMA螺栓联接的预紧力自松弛机理揭示为研究对象，构建全面考虑马氏体相变与塑性行为耦合作用，且易于有限元实现的SMA本构模型，并进一步应用于SMA螺栓连接的应力状态分析。针对SMA螺栓相变棘轮效应、马氏体塑性与蠕变耦合作用下的预紧力自松弛有限元模型构建难题，项目结合SMA螺栓联接的受载模式以及被连接件刚度模型，构建了多因素耦合作用下的一维杆单元SMA螺栓联接有限元模型，在确保求解计算精度的基础上，极大地提高了SMA螺栓预紧力自松弛分析的计算效率，验证了本项目所构建模型的工程适用性。在此基础上，通过基于力模式与位移模式的不同外载荷约束下的有限元数值分析，揭示了SMA螺栓在多因素耦合作用下的预紧力自松弛机理。同时，开展了SMA螺栓联接在循环载荷下的自松弛实验，验证了建模方法的准确性。此外，以循环载荷下的力与变形回滞曲线数据为依据，以SMA螺栓联接结构的最大能耗为目标，明确了不同规格SMA螺栓联接的最佳预紧力。

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