基于泊松效应的形状记忆合金功能梯度波纹垫变形机理及结构设计方法研究

Shape memory alloy functionally graded corrugated gasket (SMA-FGCG) can be used in nuclear power, chemical, energy, aerospace and many other fields due to its superior performance of compression - resilience and sealing . Plastic deformation should occur at peaks and troughs of the gasket to form initial sealing, and the overall structure should be in elastic state in order to provide resilient compensation to the sealing joint under the pre-load of SMA-FGCG sealing. The SAM-FGCG gasket material is bearing thermo-mechanical coupling load for a long term in its service period. Its deformation mechanism is complicated. Thermo-mechanical coupling effect, limited slip condition and load non-uniformity of the gasket material were neglected in traditional gasket design process, which makes the structural deformation theory and design method of SMA-FGCG imperfect. In this project, (1) a thermo-mechanical coupling deformation theory of SMA-FGCG based on the Poisson effect considering the limited slip condition intend to be proposed, and the deformation mechanism of SMA-FGCG under non-uniform load will be revealed. (2) A structural and functional integration design method will be established basing on the sealing tightness coefficient and the joint deformation coordination. (3) Based on SMA-FGCG finite element analysis method, a SMA-FGCG mechanical performance characterization method will be developed. This project is expected to obtain innovative achievements in SMA-FGCG deformation theory and design methods, which will provide guidance for structural design, mechanical characterization and engineering application of gaskets.

形状记忆合金功能梯度波纹垫片（SMA-FGCG）具有优异的压缩回弹性和密封性，有望应用于核电、化工、能源、航空航天等领域。SMA-FGCG在密封接头预紧时，其波峰和波谷等局部区域发生塑性变形以形成初始密封，整体结构处于弹性状态可提供弹性补偿；而在其服役过程中，长期受非均匀、波动载荷及热的耦合作用，变形机理复杂。如此，传统的忽略材料热/力耦合、载荷非均匀性和有限滑移边界的垫片设计理论与方法已无法满足SMA-FGCG的设计。因而本项目拟（1）提出考虑有限滑移边界的基于泊松效应的SMA-FGCG热/力耦合变形理论，揭示其在非均匀载荷作用下的变形机理；（2）建立基于密封紧密度和密封接头变形协调关系的SMA-FGCG结构与功能一体化力学设计方法；（3）基于有限元数值仿真方法，发展SMA-FGCG力学性能表征方法。项目预期在SMA-FGCG变形理论和设计方法上获得创新性成果，为结构设计提供理指导。

形状记忆合金功能梯度波纹垫片具有优异的压缩回弹性和密封性，集合了形状记忆合金超弹性、形状记忆性，波纹结构大弹性补偿范围大和梯度结构对非均匀载荷适应性良好等优点，可为石化装备提供较高的密封比压，提升密封均匀性和可靠性。.本项目针对热-力耦合作用下形状记忆合金功能梯度波纹垫变形机理、力学性能表征方法和设计方法，采用理论分析、实验测试和有限元仿真等手段，开展了相关研究，取得了一些开创性的研究结论：（1）NiTi合金波纹成型工艺中，定型温度是决定定型效果的主要因素，相同温度下随着定型时间的延长，最终的定型效果和形状保持的效果逐步提升，在低温定型处理时表现更为显著。（2）小节距形状记忆合金波纹试样具有更大的伪弹性变形区域，相比大节距波纹具有更大的变形刚度。（3）基于记忆合金相变本构关系的波纹垫片热力耦合有限元计算方法，相比实验误差小于15%，形状记忆效应可以大幅度地提高垫片接触应力，结构参数对垫片压缩-回弹性能的影响一致，显著性依次为：波纹间距、板材厚度、垫片高度，板材厚度、垫片高度和波纹间距对NiTi合金波纹垫接触应力影响且呈现出较高的非线性特征。（4）随着垫片被压缩量增加，由于形状记忆效应充分发挥，密封面接触应力呈现出非线性增加，NiTi合金波纹垫的泄漏率与介质内压、密封面粗糙度呈正相关。（5）所建立的形状记忆合金波纹垫片接触应力预测模型和泄漏率预测模型最大误差分别为16.1%和16.8%，可以准确预测形状记忆合金波纹垫片在预紧及操作工况下的力学性能和密封性能。（6）法兰非均匀载荷作用下，形状记忆合金均匀波纹垫中间波纹接触应力最大，采用梯度结构后，不同波纹间接触应力非均匀性有效降低，降低幅度超过36%。