【作者】 敬波；

【导师】 刘朋生； 戴文利；

【作者基本信息】 湘潭大学 ， 高分子化学与物理， 2007， 博士

【摘要】 本文在简要回顾聚合物的应力应变特性、屈服行为、脆韧转变现象以及断裂行为基本理论的基础上，从温度活化的分子活动性、应力活化的分子活动性、热历史的影响以及聚合物、聚合物共混物体系的力学行为的形态结构依赖性等方面综述了聚合物的力学行为的影响因素，进而提出了本论文工作的基本思路。首先考察了聚酰胺6（PA6）/K树脂（K）及聚碳酸酯（PC）/K共混物在不同组成、不同的测试条件下的拉伸应力应变行为。PA6/K共混物的拉伸应力应变行为随共混组成的变化很复杂；而PC/K共混物均表现出典型的非晶聚合物应力应变特性。在一定的温度范围内，PA6/K共混物的应力应变行为均表现出良好的相似性，但随着拉伸温度的提高，PA6/K共混物应力应变曲线形状有所变化；而PC/K共混物的应力应变行为在测试温度范围内均表现出良好的相似性。在很宽的应变速率范围内，随着应变速率增大，PA6/K和PC/K共混物应力应变行为的基本特征基本不变，但应力应变曲线整体上有所提升，表现为屈服应力提高。根据实验结果，应用Eyring方程研究了应变速率对共混物应力应变行为的影响，结果表明K树脂相的引入使PA6或PC基质比较容易达到屈服所需要的活化体积，反映了变形机理的改变。相容剂马来酸酐接枝K树脂共聚物（K-g-MAH）的加入，使得共混物应力集中因子变小，表明相容剂K-g-MAH对PA6/K和PC/K共混体系均有较好的增容作用。以实验结果为依据，通过计算探讨了共混物拉伸过程的总成颈变形能，认为它反应了共混物组分间相容性，并应用动态力学分析（DMTA）、扫描电镜（SEM）等测试手段进行了进一步证实。其次，观察到二次屈服现象并讨论了其形成原因与影响因素。拉伸形变过程中，含有50wt.%及70wt.%的K树脂的PA6/K共混物试样应力应变曲线上经历第一屈服点后，应力下降，然后成颈，在应变硬化过程中应力应变曲线达到第二个局部极大值点，并经过一个应力平台，发生了第二次屈服，而PA6/K其他组成的共混物则表现出普通的应力应变行为。相同组成的PA6/PS在相同的实验条件下，均未发现相似的现象。据差示扫描量热分析（DSC），大角X-射线衍射（WAXD），DMTA等测试结果，初步认为PA6/K共混物的第一次屈服是K树脂基体的屈服所致，而第二次屈服应归因于与PA6缠结的K树脂分子链中的软相（PS-co-PB）的永久塑性变形。提高拉伸温度，PA6/K共混物二次屈服现象弱化。拉伸速度提高到一定程度（200mm/min）后，不再表现出二次屈服现象。吸水率过低或过高，均不利于PA6/K共混物二次屈服行为的出现。第三，研究了PA6/K和PC/K共混物在高速拉伸条件下的脆韧转变行为。对于PA6/K共混物，随着K树脂含量的增加，PA6/K体系将发生脆韧转变，并且体系的脆韧转变速率也越高，脆韧转变温度越低。共混物脆韧转变随应变速率变化的效应可以用相应的温度变化效应表述。对于PC/K共混物，改变K树脂的含量并未明显导致PC/K共混物脆韧转变的发生。对简支梁缺口冲击样品的细微变形过程分析表明，缺口冲击变形实际上就是一种缺口尖端附近的高速拉伸变形，在这两种方法下发生脆韧转变的机理实质上是一致的。第四，利用单边缺口拉伸实验方法，研究了应变速率对PA6/K和PC/K共混物断裂行为的影响。测试速率对PA6/K和PC/K共混物断裂最大应力影响相似，最大应力均随着K树脂含量的增加而减小，随测试速率的对数值的增加而增加。测试速率对PA6/K和PC/K共混物断裂初始位移的影响都不大，但测试速率对PA6/K和PC/K共混物断裂扩展位移和断裂能量的影响有明显的不同。对PA6/K 80/20与PC/K 80/20共混物在不同温度下的应变速率影响研究进一步表明，温度显著地影响PA6/K与PC/K共混物的变形过程，低应变速率下聚合物共混物的断裂行为更易受相态结构的影响，高应变速率下聚合物共混物的断裂行为不是低应变速率下行为的简单外推。第五，对带有预制裂纹试样在低应变速率下的拉伸断裂特性的研究发现，此时试样的应力应变行为与常规试样有着显著的区别，弹性形变和屈服过程之后，均表现出较为明显的成颈和撕裂特征。研究表明，对于PA6/K体系，K树脂能显著地改善PA6材料的抗裂纹扩展能力，K-g-MAH的加入可以进一步使PA6/K共混物的裂纹阻力和塑性变形能量吸收能力均得到了提高。能量拆分的结果表明, PA6/K共混材料断裂行为的差异主要决定于材料屈服阶段的行为。对于PC/K体系，K树脂的加入并不能显著地影响PC断裂的裂纹扩展与塑性变形过程。能量拆分的结果表明，K-g-MAH的加入对PC/K共混物韧性的提高主要来自于屈服阶段抗裂纹扩展能力的改善。更多还原

【Abstract】 On the basis of a brief introduction of the theory of stress-strainbehavior, yielding characteristics including the unusual double yieldingphenomenon, brittle–ductile transition and fracture behavior of polymers,this thesis reviewed the influencing factors of deformation behavior ofpolymers from the temperature activated molecular mobility, stressactivated molecular mobility, effect of heating history and dependence ofmechanical behavior of polymers, polymer blends on the structures andmorphology and forward the purpose and arrangement of this study.Firstly the dependence of tensile stress-strain behavior of polyamide6 (PA6) /K resin (K) blends and Polycarbonate (PC) /K resin blends atvarious composition on the test conditions was investigated. The resultsshowed that PC/K blends presented the typical stress strain behavior ofnoncrystalline polymers in a wide range of composition, while the PA6/Kblends presented the varied tensile stress-strain behavior at variouscompositions. In a certain range of tensile temperatures, the stress strainbehaviors of PA6/K blends studied showed good similarity. With thetensile temperature increasing, the stress strain curves changed in a sort ofway. While the stress-strain behaviors of PC/K blends studied showed goodsimilarity in all test temperatures. In a wide range of tensile velocities,with the tensile velocity increasing, the basic characteristics of thesestress stain behavior of PA6/K and PC/K blends were unchanged while theoverall stress strain curves were raised and yielding stress depressed.According to the experimental results, the Eyring equation was usedto model the strain rate sensitivity of the stress stain behavior of PA6/Kand PC/K blends. The results showed that PA6 matrix or PC matrix wereeasy to reach the activation volume for yielding with incorporating K resin,which reflected the change of deformation mechanism. Incorporation of thecompatibilizer, maleic anhydride-grafted K resin (K-g-MAH), into PA6/Kor PC/K blends could decrease the stress concentration factors of theseblends. This implied that the compatibility between PA6/K and PC/Ksystems improved by adding K-g-MAH.On the basis of the experimental results, through the use of mathematical methods, the deformation energy of the tensile neckingprocess was discussed and deemed to reflect the compatibility of polymerblends, the results of Dynamic mechanical thermal analysis (DMTA) andscanning electron microscope (SEM) were applied to further confirm ourconsideration.Secondly the unusual double yielding was observed, and the cause offormation and the influencing factors were investigated. In the tensiledeformation of PA6/K blends containing 50wt.% and 70wt.% K resin, astress drop came after the first yield point and then the sample occurrednecking. The stress showed the second maximum with the strain hardeningprocess, then followed by a stress plateau, the second yielding occurred.But the PA6/K blends with other compositions presented usual stress-strainbehavior. No similar double yielding phenomenon was found at the PA6/PSblends with the same compositions under the same conditions. Accordingto the result of differential scanning calorimetry (DSC), wide-angle X-raydiffraction (WAXD) and DMTA analysis, it was superficially suggestedthat the first yielding of PA6/K blends might cause by the deformation ofthe K resin matrix, the second yield point might be correlated to thepermanent plastic deformation of the entanglement of PA6 chains and softphase of K resin (PS-co-PB). The double yielding phenomenon for PA6/Kblends depressed with the increasing of tensile temperature. When thetensile velocity increased to a certain velocity (200mm/min), the stressstrain behavior of PA6/K blends transformed from double yielding to usualstress strain behavior. Too high or too low moisture absorption all madeagainst the occurring of double yielding of PA6/K blends.Thirdly, the brittle–ductile transition (BDT) behaviors of PA6/K andPC/K blends in high speed tensile tests were studied. For the PA6/K blends,BDT occurred with the increase of the K resin content in high speed tensiletests. The more the K resin content was, the higher the BDT tensile speedwas and the lower the BDT tensile temperature was. The effect of tensilespeed on the BDT of polymer blends can be characterized by thecorresponding effect of tensile temperature. For the PC/K blends, BDT didnot occurr with K resin content. The micro deformation process analysis ofthe notched Charpy impact samples in impact test showed that the notchedimpact deformation was really a high speed tensile deformation at the narrow region near notch tips, The BDTs in both Charpy impact and highspeed tensile tests shared the same mechanism.Fourthly, the effect of strain rate on the PA6/ K resin and PC/K resinblends were investigated using the Single Edge Notch Tensile (SENT) test.The similar effect of test speed on the fracture maximum stress was foundin both PA6/K and PC/K blends. The maximum stress of both PA6/K andPC/K blends decreased with increasing K resin content, and increased withthe logarithm of test speed. Test speed seemed to slightly influence theinitiation phase of fracture. However, the influences of test speed onfracture propagation displacement and fracture energy for the PA6/K andPC/K blend presented distinct difference. The PA6/K and PC/K blendcontaining 20wt.% K resin was investigated further. SENT tests were doneat different temperatures over the complete test speed range. Testtemperature apparently affects plastic deformation process of both PA6/Kand PC/K blend. The fracture behaviors of polymer blends at low testspeeds was more easily affected by the morphology, the fracture behaviorsat high test speeds could not be simply expected based on the low speedsresults.Finally, the tensile fracture characteristic of PA6/K and PC/K blendssamples with pre-crack under the low strain rate were studied. The resultsshowed that with a pre-crack, the stress strain differ a lot from conventionaltensile samples: after the elastic deformation and yielding process, theyshowed marked necking and tearing process. The results showed adding Kresin to PA6 could significantly enhance the crack resistance of PA6, thefurther improvement of crack resistance and the energy absorbing abilityfor plastic deformation of PA6/K blends appeared when K-g-MAH wasincorporated. The energy partition results showed the difference of thefracture behavior was mainly from the yielding process. While adding Kresin to PC could not significantly affect the crack propagation or plasticdeformation process of PC, and the energy partition results showed theeffect of K-g-MAH on the fracture toughness for the PAC/K blends wasmainly achieved through its influence on the specific essential of fracture inthe yielding process.更多还原