热塑性聚合物材料的湿-热-力耦合循环本构关系研究

High-performanced thermoplastic polymers have beening used in the structure components subjected to cyclic loading, and fatigue failure is a main failure mode for these components. It is extremely necessary to study the fatigue behavior of thermoplastic polymers in order to ensure the safty and reliability of such structures. However, reasonable cyclic constitutive model is a key issue in the study of fatigue failure. To overcome the shortcomings in the study on the non-proportional multiaxial cyclic constitutive model of the polymers with the hygrothermal effect, this project will perform detailed experimental and theoretical research on such topics. At first, the uniaxial and nonproportional multiaxial (combined tension-torsion) cyclic deformations of three kinds of thermoplastic polymers are observed under the conditions of room-temperature and constant humidity, varied temperature and constant humidity, and varied temperature and humidity. The effects of humidity and temperature on the cyclic deformation of the polymers are addressed during the uniaxial and nonproportional multiaxial cyclic loading; and the internal heating mechanism of the polymer during the cyclic deformation and the interaction between the internal heating and cyclic deformation are deduced.Then, based on the results obtained from the experimental observations, a thermo-mechanical coupled and hygro-thermo-mechanical coupled cyclic constitutive models are constructed to describe the hygro-thermo-mechanical cyclic deformation of the polymers in the framework of irreversible thermodynamics and small-strain continuum mechanics.The successful construction of hygro-thermo-mechanical cyclic constitutive model will make a important progress in the field of cyclic constitutive models concerning the coupled multifield problems, and the achievements from this project is of great scientific significance.Moreover, the established cyclic constitutive model can be directly used in the prediction of fatigue life and assessment of safty and reliability of structure components made from the polymers. So, the established model has many potential applications in the engineering.

高性能聚合物材料已经越来越多地应用于承载结构领域，疲劳失效是聚合物材料结构构件失效的主要模式，而材料的循环本构关系是结构构件疲劳失效分析和可靠性评价的基础。本项目针对聚合物材料湿热环境下的非比例多轴循环本构关系研究方面的不足，开展如下系统的实验和理论研究：首先通过室温常湿、变温常湿和变温变湿条件下系统的单轴和非比例多轴(拉-扭组合)循环变形实验研究，揭示聚合物材料的循环变形特征和内部热效应形成机制以及湿热效应与循环变形之间的耦合作用；然后在实验揭示的演化规律基础上，基于不可逆热力学和小变形连续介质力学框架，建立聚合物材料热-力和湿-热-力耦合的循环本构模型。湿-热-力耦合循环本构模型的建立是材料循环本构关系研究方面的一个重大突破，具有重要的科学意义；同时，研究成果可直接应用于聚合物构件湿热环境下的疲劳寿命预测和结构可靠性评估中，解决迫切的工程需求，从而具有较高的工程应用价值。

鉴于高性能热塑性聚合物材料越来越多的应用需求以及疲劳失效是其结构构件失效的主要模式，本项目针对热塑性聚合物材料湿-热耦合循环本构关系研究方面的不足，开展了系统的实验和理论研究，建立相应的循环本构关系。具体研究内容和主要研究成果为：（1）通过室温常湿、变温常湿和变温变湿条件下系统的单轴和非比例多轴循环变形（含棘轮行为）实验研究，揭示了三种热塑性聚合物材料（即聚碳酸酯PC，超高分子量聚乙烯UHMWPE和尼龙PA6）的循环变形特征和内部热效应形成机制以及湿-热效应与循环变形之间的耦合作用；同时揭示了三种材料的单轴和多轴非比例循环变形行为对加载水平、加载速率、加载路径和加载历史以及环境温度和相对吸湿度的依赖性。（2）在常温常湿实验揭示的循环变形演化规律基础上，基于不可逆热力学和小变形连续介质力学框架，建立了合理考虑粘弹性和粘塑性共同发展的粘弹性-粘塑性循环本构模型。（3）在已建立的粘弹性-粘塑性循环本构模型基础上，引入在较高加载水平和较快加载速率下的聚合物材料外部热环境、内部热效应和循环变形之间的耦合作用机制，建立了聚合物材料热-力耦合的循环本构模型。（4）基于变温变湿实验揭示的聚合物材料外部热环境、内部热效应、湿分扩散（非Fick扩散）和循环变形之间的耦合作用机制，进一步考虑湿分扩散对热-力耦合循环变形行为的影响，拓展建立了合理考虑聚合物材料湿-热-力耦合循环变形特征的循环本构模型，并验证了模型的合理性。.湿-热-力耦合循环本构模型的建立是材料循环本构关系研究的一个重大突破，具有重要的科学意义；同时，研究成果可直接应用于聚合物构件湿热环境下的疲劳寿命预测和结构可靠性评估，解决迫切的工程需求，从而具有较高的工程应用价值。在资助期内，共发表标注论文21篇，其中SCI 收录14 篇；授权发明专利3项；已培养博士毕业生2名，硕士毕业生2名；项目主持人受聘为长江学者特聘教授，入选中组部“万人计划”领军人才。