【作者】 孙鹰；

【导师】 张平；

【作者基本信息】 湘潭大学 ， 一般力学与力学基础， 2005， 硕士

【摘要】 聚合物材料的广泛应用迫使人们越来越重视它的强度和断裂性能。高聚物是典型的粘弹性材料,在外载作用下其变形不仅与时间、温度相关,而且还与应变率相关,在变形过程中通常会出现非线性变形和变形局部化现象,表现为银纹化或剪切带的形成以及颈缩变形,它们往往是材料宏观失效的先兆。研究高聚物变形和断裂过程中与时间、温度和应变率相关的力学行为及银纹的扩展规律和材料断裂机理,具有重要的理论意义和应用价值。 自 1949 年 Sauer 和 Hsiao 等人研究聚合物的银纹现象以来,学者们基于不同的知识背景,运用不同的研究技术和方法,从不同角度对银纹进行了广泛研究,并提出了各自的观点,建立了一些相应的模型。如有银纹的结构模型和力学模型、银纹形成和引发的力学判据及其微观机理和裂纹尖端银纹损伤的应力分布模型等。本文通过对 PMMA 材料进行在不同应变率下的单轴拉伸实验,得到了应变率相关的应力-时间关系式,同时结合显微镜银纹观察实验,分析讨论了 PMMA 在不同应变率下银纹分布规律以及断裂状态下的银纹密度随应变率变化的规律。 从能量的观点出发,提出中值应力概念。实验结果表明,PMMA 材料断裂时的中值应力与应变率无关,可将其作为一个表征 PMMA 材料破坏的参数。更多还原

【Abstract】 The extensive applications of the polymer materials necessitate people paying more and more attention to their strength and fracture properties. Polymers are a kind of typical viscoelastic materials, whose deformation not only is related with time, temperature, but also strain rate on loading. Nonlinear deformation and localized deformation usually occur, that is to say, they display crazing, shear zone and neck deformation which often are the foreboding of macro-failure of materials. Therefore it is important for theoretical meaning and practical value to study mechanic behaviors related with time, temperature and strain rate in the processing of deformation and fracture, and the development law of craze and the mechanism of material fracture. Since Sauer and Hsiao etc. studied the phenomenon of polymeric craze in 1950,based on their different knowledge backgrounds and by the different technica and methods, the researchers have carried out the extensive research on craze from different viewpoints and put forward each standpoint and established some relative models, such as the construction models and mechanic ones of craze, mechanic criterions and microscopic mechanisms on the initiation and shape of craze and models of stress distribution of craze damage at the tip of crack etc.. The paper has still gotten the strain-rate-dependent stress-time function of PMMA material, by the uniaxial tension test. At the same time, the craze distribution law and the strain-rate-dependence of the craze density by microscope test of craze. The paper has proposed a concept of median stress from the standpoint of energy. It has resulted the critical median stress of PMMA has nothing to do with strain rate at the range of the given strain rate, so it is represented as a parameter to scale the break of PMMA.更多还原