非晶态聚合物的应力波动行为研究

发布时间：2018-03-21 10:43

本文选题：PET　切入点：PC　出处：《长春工业大学》2017年硕士论文　论文类型：学位论文

【摘要】：应力波动现象是一种特殊的力学现象。通常当拉伸速率恒定时,聚合物在屈服后应力随应变的增加呈较为平滑的变化。然而,在特定条件下,某些聚合物的应力会随着应变的增加呈周期性波动。这一现象通常在非晶态但能结晶的聚合物(例如PET)中产生,对于这类聚合物的应力波动行为已有很多报道,但波动机理还尚存争议。另外,非晶态且不能结晶聚合物(例如PC)的应力波动现象及成因研究也鲜有报道。因此,本论文将从拉伸行为、热行为、结晶度以及宏观、微观形貌角度,详细分析、对比非晶态但能结晶聚合物(PET)和非晶态且不能结晶聚合物(PC)应力波动的成因,以期从分子水平上初步揭示不同聚合物产生应力波动的原因。1.研究了非晶态但能结晶聚合物PET的应力波动现象。PET应力波动行为具有分子量和拉伸速率依赖性。拉伸后试样应力波动区域宏观形貌上呈明暗交替的带状结构。通过SEM和DSC实验确定PET应力波动区域的微观结构,并证实了试样内部空化现象只是应力波动的微观结果,而应力波动曲线上的应变硬化和应变软化交替作用是由于样条“明带”和“暗带”区域的结晶度大小不同所致。2.研究了非晶态且不能结晶聚合物PC的应力波动现象。PC应力波动行为具有拉伸速率和老化时间依赖性。拉伸后试样宏观形貌不是典型的明暗交替的带状结构,而是准平行于断裂方向的透明棱状结构。通过DSC、IT和SEM实验得出,PC应力波动的成因与固有机理均不相同,是物理老化和应力活化交替作用的结果,其中物理老化使试样应力增加,而应力活化使应力减小。此外,为了更加直观的描述应力波动曲线中一个波动周期的变化过程,本文通过一个类似于两元件Maxwell单元的模型来模拟PC的应力增加阶段和应力减小阶段。
[Abstract]:Stress fluctuation is a special mechanical phenomenon. Usually, when the tensile rate is constant, the stress of the polymer changes smoothly with the increase of strain after yield. However, under certain conditions, The stress of some polymers fluctuates periodically with the increase of strain. This phenomenon usually occurs in amorphous but crystallizable polymers (such as PET). The stress fluctuation behavior of some polymers has been reported. However, the fluctuation mechanism is still controversial. In addition, there are few reports on stress fluctuation phenomena and causes of amorphous and uncrystallized polymers (such as PCS). Therefore, this paper will focus on tensile behavior, thermal behavior, crystallinity and macroscopical properties. The causes of stress fluctuation between amorphous but crystallized polymers (PET) and amorphous and uncrystallized polymers (PCs) were analyzed in detail. In order to reveal the reason of stress fluctuation in different polymers at molecular level, the stress fluctuation phenomena of amorphous but crystallized polymer PET were studied. The stress fluctuation behavior of PET was dependent on molecular weight and tensile rate. The microstructure of the stress fluctuation region of PET was determined by SEM and DSC experiments. It is proved that the cavitation in the specimen is only the microcosmic result of the stress fluctuation. The alternate effect of strain hardening and strain softening on the stress fluctuation curve is due to the difference in crystallinity between the "bright zone" and "dark zone" of the spline. 2. The stress fluctuation of amorphous and uncrystallized polymer PC is studied. The stress fluctuation behavior of PC is dependent on tensile rate and aging time. By DSC-IT and SEM experiments, it is found that the origin and inherent mechanism of stress fluctuation of PC are different, which is the result of alternating action of physical aging and stress activation, in which physical aging increases the stress of the specimen. In addition, in order to describe more intuitively the variation of a fluctuation period in the stress fluctuation curve, In this paper, a model similar to the two-element Maxwell element is used to simulate the stress increasing and decreasing phases of PC.
【学位授予单位】：长春工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O631.21

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