非晶态高聚物热力学本构模型及其在变形局域化行为表征方面的应用

Amorphous polymers are widely used as structural and functional materials. The physical aging behavior of amorphous polymer is an important research area for a long period of time. As aging, the nonequilibrium structure continuously evolves towards the equilibrium state. The change of nonequilibrium structure has a significant effect on the macroscopic mechanical response of amorphous polymers, such as deformation localization behaviors. In this project, we plan to combine experiments and theory to investigate the nonequilibrium thermodynamic behaviors of amorphous polymers and its effects on the deformation localization phenomena. We will investigate the influence of temperature, strain rate and aging on the stress response. The experiments will also be conducted to describe the effects of aging and mechanical predeformation on the heat capacity. The digital image correlation and infrared thermometry will be combined to measure the deformation localization behaviors. The thermomechanical coupled 3D model, which introduces the effective temperature as a thermodynamic state variable to describe the nonequilibrium structure, will be developed for finite deformation behaviors of polymers. The model will be employed to investigate the temperature, nonequilibrium structure and strain hardening effects on the onset and propagation of deformation localization behaviors. This project will benefit the development of nonequilibrium thermodynamic theory and promote the engineering applications of amorphous polymers.

非晶态高聚物作为一种广泛应用的结构和功能材料，其物理老化行为一直是国内外学者长期研究的重点。随着物理老化现象的发生，高聚物的非平衡态结构逐渐接近平衡态，而非平衡态结构的动态演变又会显著影响高聚物变形局域化等宏观力学行为。本项目拟结合实验测试和理论模型系统地研究非晶态高聚物的非平衡态热力学行为及其对变形局域化的影响。在实验方面，拟研究不同温度、应变率以及老化条件下的应力应变规律，以及不同老化和预变形条件下的热容演变规律；同时开展基于数字图像相关技术和红外测温技术的实验来表征变形局域化行为。在理论方面，引入等效温度作为热力学变量来表征高聚物的非平衡态结构的状态，并建立热力耦合三维有限变形模型，进而研究温度变化、非平衡态结构的演变以及应变强化效应对变形局域化产生和发展的影响。本项目的研究对非晶态高聚物基础理论的发展和工程应用都有着重要意义。

针对玻璃态聚合物的热力学性质和变形局域化行为，开展了深入的实验和理论研究。在实验方面，开展实验系统地研究玻璃态聚合物的力学行为，包括不同温度、应变率下的应力响应，以及不同老化、预变形和应变率条件下的变形局域化行为，包括颈缩的产生和发展，通过数字图像相关法和红外测温技术系统的测量了应变场和温度场。在理论方面，建立了基于等效温度的本构模型，本构模型能够准确描述不同温度、应变率、老化条件和预变形的应力响应。上述本构模型被进一步植入到有限元软件中，有限元模型能够较好的模拟玻璃态聚合物的热力耦合行为。依托本项目以第一/(共同)通讯作者发表SCI论文14篇，多篇论文发表在JMPS、IJP等力学主流期刊。项目负责人获得国家自然科学基金优秀青年基金资助，培养博士后2名，博士研究生4名等。