形状记忆凝胶相变-扩散-应力耦合大变形本构关系及其实验验证与数值实现

Shape memory hydrogel (SMH) is one of the most interesting hydrogels which can remember its original shape, keep the temporary deformed shape at low temperature and recover to the original shape spontaneously by heating. In wet environment,SMHs are usually soft materials with predominant water, and a typical thermo-chemo-mechanical coupled performance and large-deformation commonly occurs during a shape memory cycle. The present project aims to develop a novel constitutive theory for the transformation-diffusion-stress coupled large deformation and a FEM-based numerical technique for modelling the multifield response of SMHs in wet environment. Firstly, a series of experiments on a representative SMH will be conducted at different temperatures and chemical environments for the quantitative characterization of the multi-field responses. Secondly, a coupled thermo-chemo-mechanical constitutive theory for large deformations will be formulated to characterize the response of thermally actuated SMHs within the framework of thermodynamics. Thirdly, a numerical technique which is suitable for the large deformation analysis will be developed by implementing the developed constitutive model into the finite element method. Finally, the typical experiments will be conducted to validate the reliability of the theoretical model and its numerical implementation.The successful implementation of this project will provide an insight into the mechanism of multi-field coupling and shape memory behaviour, and lead to an extremely useful tool for the design and analysis of various SMH-based biomedical devices.

作为一种智能软材料，形状记忆凝胶（SMH）具有记忆其初始形状的特性，这种湿环境下的形状记忆凝胶通常是柔软和富含水分的，在一个形状记忆循环中表现为明显的热-化-力学耦合行为和非线性大变形特征。本项目旨在发展一种相变-扩散-应力耦合的大变形本构理论和基于有限元的数值方法，研究形状记忆凝胶在湿环境下的多场响应。设计实验方案，定量表征形状记忆凝胶在不同温度和化学环境下的多场响应和材料性能；基于实验现象和数据，在热力学框架内建立相变-扩散-应力耦合的大变形本构理论，描述热驱动形状记忆凝胶的变形响应；将建立的本构模型与有限元方法结合，发展适用于多场耦合大变形分析的数值技术；利用典型实验数据，验证理论模型与数值方法的可靠性。本项目将有助于深刻理解形状记忆凝胶的多场耦合与形状记忆机理，并对基于形状记忆凝胶的各种结构和器件的设计与分析提供有力工具。

形状记忆凝胶是一种新型而独特的凝胶材料，可以对外界的刺激发生可逆的变化，从而表现出形状记忆的特性，在生物医学和传感器方面具有广泛的应用前景。但其对外界刺激响应的多场耦合和形状记忆机理尚不完全清楚，因此发展准确而可靠的理论模型和数值模拟技术有助于我们深刻理解其多场耦合变形机理，对凝胶结构与器件的设计和应用具有基础性的理论指导意义。本项目针对形状记忆凝胶，从理论建模和数值模拟方面对其多场耦合大变形行为进行了研究，主要内容包括：凝胶在大变形条件下相变-扩散-应力耦合行为本构关系的建立和非线性数值计算方法的发展；形状记忆热黏弹性本构关系的建立和典型形状记忆凝胶结构或器件的数值模拟。.本项目基于连续介质和热力学理论框架，建立了形状记忆凝胶相变-扩散-应力耦合的大变形本构关系，根据变分原理，推导得到了化-力耦合有限元计算公式，编写开发了有限元用户子程序，发展了多场耦合的非线性有限元数值计算方法；研究了凝胶肿胀/收缩引起的形状记忆行为及温度对热敏感水凝胶体积相变的影响，分析了温敏水凝胶复合结构由于体积相变引起的双稳态特性，并基于自由能密度函数采用数值方法求解了相转变温度，研究了凝胶微结构参数对相转变温度的影响；根据物质扩散和热扩散之间的类似性，对一维化-力耦合问题进行了理论求解，得到了特定边界条件下各物理场的解析表达式；基于Kelvin-Voigt模型，建立了形状记忆热黏弹性本构方程，并利用该本构关系对簧片、隔膜及支架等智能结构的形状记忆过程进行了模拟分析；针对化学-力学耦合作用下凝胶断裂及凝胶双材料界面断裂力学进行了研究，结果表明界面处的材料属性对界面裂纹的应力场与断裂参数有着明显的影响，两种材料弹性模量比越大，破坏时内聚力法向位移与切向位移的比值越大。.依托本项目，课题组发表SCI论文27篇，中文期刊论文5篇，出版学术专著2部,发明专利4件，国内外学术会议报告36次,出站博士后3名，毕业博士生5名，毕业硕士研究生11名。