冲击拉伸下环氧树脂材料非线性粘弹性本构响应与断裂行为

Epoxy resin polymeric materials and their composites have been used widely in engineering applications, which are often subjected to dynamic loading and high strain rate deformation during in-serive life. The viscoelastic mechanical behaviours of polymeric materials seriously depend on the strain rate. It is necessary to investigate the dynamic mechanical responses of epoxy resin polymeric materials under impact loading. It is a challenge to design a valid dynamic tensile experiment for a polymeric materials due to their low strength,low wave velocity and low impedance. In this preject, based on ultra high speed camera and all fiber laser doppler velocimeter, the traditional split Hopkinson tension bar and wave propagation inverse analysis (WPIA) technique are revised and developed.The dynamic tensile behaviour, the nonlinear viscoelastic wave propragation and spallation of the thermoset epoxy resin under impact tension loading have been determined.Strain rate effects on the tensile behaviours of epoxy resins are discussed. The interdependence between the basic characters of viscoelastic waves and the constitutive responses is studied. The influences of the stress conditions on spallation of epoxy resins are explored. Based on Zhu-Wang-Tang's constitutive relation, a new damage-modified viscoelastic tensile constitutive relation is proposed, and a critical damage failure criterion is suggested. The parameters of constitutive relation is determined based on the experiemntal results.These results will provide insight into improving the resistance of impact damage and failure for epoxy resin materials and their composites in the actual engineering applications.

环氧树脂及其复合材料在工业领域应用广泛，在服役期内其经常会承受冲击载荷和高速率的变形，而它的粘弹性特征导致其力学性能强烈依赖于应变率。因此，迫切需要开展环氧树脂材料在冲击加载下的力学性能研究。然而环氧树脂材料的低强度、低波速、低阻抗等特性给材料动态力学性能测试带来了困难,尤其是冲击拉伸性能测试。本项目拟借助超高速摄像技术和全光纤激光多普勒质点速度测量系统，发展和优化分离式Hopkinson拉杆和波传播反分析实验技术，系统地研究环氧树脂材料的动态拉伸本构响应、非线性粘弹性波传播特性以及层裂行为，讨论应变率效应、波传播与本构特性之间的相互依赖性以及应力状态对层裂行为的影响，构建一个含损伤非线性粘弹性拉伸本构关系及临界损伤度断裂准则，获得环氧树脂材料的宏观冲击拉伸力学响应参数以及断裂机理方面的深刻认识，探索提高环氧树脂材料抗冲击损伤与失效的有效途径。

聚合物及其复合材料在服役期内其经常会承受冲击载荷和高速率的变形。本项目旨在发展聚合物材料动态力学性能测试新技术，开展典型聚合物材料动态力学性能实验研究。基于超高时空分辨率相机和数字图像相关性分析方法以及全光纤激光多普勒质点速度多点测量技术，分别发展了分离式Hopkinson杆实验系统的非接触光学测试技术和长杆试件拉氏反分析实验技术。在分离式Hopkinson杆实验中，基于试件表面全场应变测量信息讨论了试件应变均匀性问题，提高了材料动态拉伸应力-应变曲线的实验测量精度；基于激光正入射和激光斜入射两种测试手段，建立了杆上和试件上应变测量的激光干涉测试技术，该技术具有免标定、抗干扰、可靠性高等诸多优势。在拉氏反分析实验中，通过超高时空分辨率DIC技术和全光纤激光多普勒质点速度多点测量技术，获得不同位置处长杆试件表面粒子速度场，基于一维应力波守恒方程，数值求解了应力时程和应变时程，并实现应变时程的自洽性验证，保证了拉氏反分析的可靠性，从而建立了聚合物材料动态应力-应变曲线测试新技术。基于上述新发展的动态实验技术，系统开展了不同应变率和应力状态加载下典型聚合物材料的动态力学响应和断裂行为实验研究，获得了不同应变率下典型聚合物材料应力-应变关系曲线，提出了描述高应变率下环氧树脂力学性能的非线性Kelvin-Voigt粘弹性体拉伸本构关系，阐明了应力状态和应变率对环氧树脂材料动态拉伸断裂强度的影响规律；基于拉伸试件断口的显微分析，揭示了环氧树脂材料和纤维增强环氧树脂复合材料的断裂机制及其对应变率的依赖性。为了提高环氧树脂材料性能，探索性研究了聚多巴胺改性氧化石墨烯增强环氧树脂复合材料的制备工艺及力学性能，解决氧化石墨烯在环氧树脂中分散均匀问题，拉伸强度明显提高。研究结果将为环氧树脂及其纤维增强复合材料在工程应用中强度可靠性分析提供重要的基础实验数据，并可推广应用到其他聚合物冲击拉伸性能研究中。