有限变形下热致形状记忆聚合物热-力耦合循环变形行为及其本构描述

The thermo-induced shape memory polymer has been successfully applied in many fields, such as aerospace and smart biomedical devices and so on, due to its unique shape memory effect and excellent biological compatibility. The key mechanical issues of such a smart material consist of the structural and functional fatigues under the cyclic thermo-mechanical loading condition. Detailed macroscopic experiments are performed to investigate the thermo-mechanical cyclic deformation of thermo-induced shape memory polymer under the pure mechanical and shape memory cyclic loading conditions with different loading modes and levels and at various loading rates by employing the supplementary technologies of the infrared temperature measurement and non-contact strain measurement. The couple of internal thermal effect and cyclic deformation, and its influence on shape memory degradation are revealed. Then, based on the theory of multiple natural configurations, a thermo-mechanically coupled three-dimensional cyclic constitutive model is established in the framework of thermodynamics at finite deformation by employing the multiplicative decomposition of deformation gradients and introducing the evolution laws of internal variables and the dissipation and thermal conduction equations. Moreover, the established model is implemented into the finite element code ABAQUS by the user defined material subroutine, and then the prediction capability of the proposed model to the thermo-mechanically coupled cyclic deformation behaviours of shape memory polymer and its structure is validated. The obtained findings can provide a theoretical foundation and analysis method for evaluating the structural and functional fatigues of shape memory polymer components, and promote wider engineering application of such a smart material.

热致形状记忆聚合物因其特有的形状记忆效应和良好的生物相容性，已成功应用在航空航天和智能医疗设备等领域，循环热-力耦合载荷作用下的结构性和功能性失效是该类智能材料应用中的关键力学问题。本项目针对热致形状记忆聚合物的热-力耦合循环变形行为，通过不同加载模式、加载水平和加载速率的机械载荷循环和形状记忆循环变形宏观实验，结合红外测温和非接触应变测量等辅助手段，揭示热致形状记忆聚合物内部热效应与循环变形的耦合作用及其对形状记忆效应退化的影响；通过多重自然构型的变形梯度乘法分解，引入内变量演化方程、耗散方程和热传导方程，在热力学框架下建立有限变形下的热-力耦合三维循环本构模型；进而利用ABAQUS的用户子程序将建立的模型进行有限元移植，验证模型对该材料和结构热-力耦合循环变形行为的预测能力。项目成果为形状记忆聚合物器件的结构性和功能性疲劳评估提供理论基础和分析手段，促进该类智能材料更为广泛的工程应用。

针对热致形状记忆聚合物的热-力耦合循环变形行为，开展了系统的宏观实验、本构模型和数值模拟研究。通过不同加载模式、加载水平和加载速率的机械载荷循环和形状记忆循环变形实验，获取了形状固定率和回复率对加载条件的依赖性，揭示了材料内部热生成与循环变形的耦合作用及其对形状记忆效应的影响。在有限变性框架下，通过变形梯度乘法分解，根据严格的热力学过程推导出本构方程和热平衡方程，建立了热-力耦合三维本构模型，该模型能够描述不同加载速率下的应力-应变关系和内部热生成。进而基于相变理论，在玻璃相中引入背应力项和剪切抗力温度相关项来反映温度对机械变形的影响，通过在玻璃相和橡胶相体积分数中引入移位因子来描述升降温过程中不同的机械响应，建立了大变形形状记忆本构模型。最后，利用ABAQUS的用户材料子程序对本构模型进行了有限元实现，验证了该模型对不同温度下的力学响应和形状记忆效应的预测能力，并应用于隐形矫正器、血管支架、机械手等智能器件的优化设计中。项目成果为形状记忆聚合物器件的结构性和功能性疲劳评估提供理论基础和分析手段，促进该类智能材料更为广泛的工程应用。项目执行期间共发表项目相关论文12篇，其中SCI收录9篇，中文核心期刊论文3篇；主编专著1部，英文章节1章；授权发明专利2项，实用新型专利5项；培养博士生4名，硕士生4名；作国内学术会议邀请报告9次，国际学术会议报告10次，开展国内外学术交流合作10次。