HDPE蠕变行为的研究

研究HDPE的蠕变行为不仅有助于从分子运动机理上揭示聚合物的黏弹性行为,还能够预测材料使用过程中的尺寸稳定性及长期承载能力,减小工程设计误差,确保材料使用的安全性,因而具有重要的理论意义和实用价值。回顾了蠕变理论的发展,综合了近年来有关HDPE蠕变行为及形变机理的研究进展,并以HDPE单向拉伸格栅为例简要分析了此项研究的发展及应用前景。     

热塑性高分子薄膜蠕变模型的研究

在研究热塑性高聚物变压力拉伸蠕变过程的基础上,应用Boltzmann原理对Maxwell Voigt粘弹性模型进行了改进,建立新的蠕变模型及数据处理软件。实验证明此模型可以较好地应用于PVC薄膜拉伸蠕变试验研究中     

连续纤维复合材料环形试样蠕变行为研究

对连续玻璃纤维复合材料进行了拉伸蠕变试验研究,为了模拟复合材料在压力容器中的受力状态并减少夹具加持力对试样的影响,采用环形复合材料试样拉伸蠕变试验方法。对复合材料环形试样的拉伸强度及不同应力等级下的拉伸蠕变性能进行了研究,并基于时间?应力等效原理,通过双对数法拟合出压力容器50年使用寿命时复合材料的最大蠕变应力,为复合材料压力容器的设计提供支持。并基于时间?应力等效原理,通过双对数法拟合出压力容器50年使用寿命时复合材料的最大蠕变应力应低于其拉伸强度的44.4 %。     

YR-I型压缩蠕变仪的研制及应用

根据高分子材料的压缩蠕变原理,设计并制造了YR-I型压缩蠕变仪,并编制了数据处理软件,该仪器可测定不同温度和压力条件下高分子材料的压缩蠕变性能,并可计算材料的本体粘度、压缩永久变形等性能参数。实际应用证明,该仪器适合表征各类橡胶的压缩蠕变性能。     

《聚合物流体拉伸流变学》出版

<正>我国首部聚合物拉伸流变学专著《聚合物流体拉伸流变学》(ISSN 978-7-5623-4683-8)已由华南理工大学出版社出版。该书内容分为12章,阐述了聚合物流体(含熔体和溶液)拉伸流变学的基本理论和方法;分析和讨论了聚合物材料(包括共混物和复合材料)加工及成型过程中的流体拉伸流变行为及机理;论述了聚合物流体拉伸流变特性的测量方法及原理,典型的聚合物流体拉伸流变特     

万用蠕变仪性能及应用

<正> 大庆石化总厂研究院1988年从意大利CEAST公司引进一台万用蠕变仪.代号为6800。1990年初进行了安装调试,现已投入使用。该仪器主要用于测试塑料的拉伸、弯曲、压缩蠕变性能,测试方法采用     

塑料土工格栅蠕变性能测试方法探讨

研究了塑料土工格栅蠕变性能与拉伸强度之间的关系,并证明了塑料土工格栅蠕变行为符合时温等效原理,应用时温等效原理可在较高温度下试验得到较低温度下更长期的设计强度。     

聚苯乙烯/聚丙烯酸丁酯自交联胶乳互穿聚合物网络的力学性能和动态力学性能

采用种子乳液聚合制备了聚苯乙烯/聚丙烯酸丁酯自交联胶乳互穿聚合物网络。拉伸实验结果表明,用双丙酮丙烯酰胺和己二酸二酰肼自交联的胶乳互穿聚合物网络(LIPN)比相应的胶乳互穿聚合物网络具有较高的拉伸强度,并且随双丙酮丙烯酰胺用量的增加,拉伸强度增加以及永久变形降低,但离子键和氢键交联的LIPN具有很高的扯断伸长率和很大的永久变形,这些说明用双丙酮丙烯酰胺和己二酸二酰肼界面共价键交联能很好地改善力学性能和抗蠕变性能。动态力学谱结果表明,用双丙酮丙烯酰胺和己二酸二酰肼交联的LIPN比相应的LIPN以及离子键和氢键交联的LIPN具有较好的组分相容性和阻尼性能。     

湿度传感器及其应用

本文综述了氯化锂类、聚合物类和陶瓷类湿度传感器的原理,结构及湿敏性能。还讨论了三类湿度传感器的技术情况。     

隔振橡胶材料基于简单应变模式的 蠕变特性研究

对隔振橡胶材料的单轴拉伸应力松弛试验数据进行归一化处理,应用Prony级数模型对其应力松弛试验数据进行拟合,获得对应的粘弹本构参数。将表征粘弹特性的Prony级数因子引入Ogden超弹本构方程,获得隔振橡胶材料基于时间效应的本构方程,进而分析单轴拉伸、双轴拉伸和平面拉伸模式的蠕变特性,最后采用沙漏弹簧进行蠕变仿真与试验验证。该蠕变仿真预测方法为隔振橡胶材料的粘弹试验、蠕变计算和工程应用提供一种新思路。     

Accurate measurement of creep of nylon-6,6 at constant temperature and humidity

This paper describes a purpose-built environmental chamber housing three creep machines for accurate measurements of creep in a hygroscopic polymer. The environmental chamber controls the temperature to within ±0.1°C and the relative humidity to within ±1% r.h. or better. The creep machines are sufficiently accurate to limit the error in the measured modulus to ±0.4% at the 0.1% strain level. Also described are new designs of lateral extensometers and of a simplified zero-load control machine based on similar principles to those of the creep machines, but which can also be adapted for accurate creep tests on very small test pieces using loads of as little as 1 N. Creep results are presented of nylon-6,6 at several constant stresses and relative humidities at 23.5°C, each test lasting for six weeks. Evidence is given, in the form of 24 h creep curves, of an aging phenomenon in nylon-6,6: a progressive increase in stiffness with storage time at the test condition following humidification at 90% r.h.     

The viscoelastic extension of polymer fibres: complex loadings

The response of oriented polymer fibres to complex loading patterns is investigated. It is shown that the creep and stress relaxation is non-linear with the applied stress. The ratio of the creep rate and the stress-relaxation rate is given by the local slope of the tensile curve and not by the elastic modulus as predicted by linear viscoelastic theory. A consequence of this observation is that viscoelastic and yield deformations are coupled. By analysing the results of the step-creep and the strain-relaxation-strain experiments performed on poly(p-phenylene terephthalamide) fibres, it is shown that the linear superposition principle does not apply to the tensile deformation of polymer fibres above the yield point. Finally the various components of the tensile deformation that should be covered by a constitutive equation for polymer fibres are discussed.     

Creep resistant polymeric nanocomposites

In the present study, one of the unique improvements in polymer nanocomposites has been detected. Only with a very low volume fraction of inorganic nanoparticles, the creep resistance of thermoplastic could be significantly improved. 21 nm-TiO₂/PA6,6 nanocomposites were compounded using a twin-screw-extruder. The final specimens were formed using an injection-moulding machine. Static tension and tensile creep tests were carried out at room and an elevated temperature (50 °C). It was found out that the nanoparticles contributed to a remarkable reduction of the creep rate under various constant loads at both temperature levels. It is assumed that the nanoparticles restrict the slippage, reorientation and motion of polymer chains. In this way, they influence the stress transfer on a nanoscale, which finally results in these improvements.     

Tensile creep behaviour of polymethylpentene–silica nanocomposites

For the first time, poly(4‐methyl‐1‐pentene) (PMP) nanocomposites were prepared by melt compounding 2 vol% of fumed silica nanoparticles, in order to study the role of the nanofiller surface area and functionalization on the tensile mechanical response of the material, with particular focus on its creep behaviour. The high optical transparency of the polymer matrix was substantially preserved in the nanocomposites, while the mechanical properties (in particular the creep stability) were improved. Dynamic mechanical thermal analysis showed an improvement of the storage modulus, more evident above the glass transition temperature of the polymer matrix. Uniaxial tensile tests evidenced that the elastic modulus of the material was positively affected by the presence of silica nanoparticles, even if a slight reduction of the strain at break was detected. The reduction of the tensile creep compliance was proportional to the surface area of the nanofiller, being more evident at high stresses and elevated temperatures. Findley's law furnished a satisfactory fitting of the creep behaviour of the composites, even at high temperatures. It clearly emerges that the incorporation of fumed silica nanoparticles in PMP can be an effective way to overcome the problem of the poor creep stability of polyolefins, especially at high temperatures and high stresses. Moreover the possibility of retaining the original transparency of the material is fundamental for the production of completely transparent PMP components. Copyright © 2010 Society of Chemical Industry     

Creep of nylon-6,6 during concurrent moisture changes

Dimensional changes of nylon-6,6 during moisture changes under zero load and under applied tensile loads have been measured. These moisture changes included both simple sorption or desorption and humidity cycling. The anomalous creep behaviour that had been observed with wood was not found, but on the contrary it was found that the creep behaviour in changing humidities could be approximately predicted from creep data at constant stress and humidity. The method of prediction assumed that the instantaneous mean moisture content controlled the behaviour. This relatively simple approach was compared with a lengthy ‘explicit’ method and found to give almost identical results.     

Temperature-dependent mechanical properties and constitutive equation of cellulose nitrate

The strain-time response under tensile loading (creep tests) and the stress strain response under constant tensile stress rate (proportional loading tests) have been evaluated at 4 temperatures 20, 45, 55, and 65°C, for samples of cellulose nitrate. A time-dependent constitutive equation (or stress-strain relation) for the nonlinear visco-elastic material is deduced from invariant theory with a hypothesis of a creep potential. The procedure for determining the seven material constants involved in the deduced constitutive equation is described for the creep and proportional loading tests and the variation of these constants with temperature is presented. The deduced constitutive equation gives good agreement with the actual observations for the creep and proportional loading tests, independent of the values of temperature, creep stress, or stress rate.     

早龄期高强混凝土拉伸徐变特性

通过早龄期混凝土拉伸基本徐变的实验,研究了不同水灰比,加载龄期、加载初始应力强度比(应力水平)等参数条件下的早龄期高强混凝土拉伸徐变特性.结果表明:龄期0.5,0.75d和1d加载的混凝土表现出较大的徐变变形,并且徐变速度在持续加载一段时间后随龄期的推迟而急速下降:龄期0.5,0.75d加载的混凝土徐变表现出较大的非线性,同一加载龄期下,加载初始应力强度比越大,比徐变越大,加载初期的徐变速度越快;但加载龄期在1,3,7d的混凝土徐变仍表现出较明显的线性特征.同一加载龄期、同一加载应力强度比的条件下,水灰比越大,比徐变越大,而且加载龄期越早,比徐变的差异越明显.     

Effects of a fluid environment on the stiffness of polymers

The effects of an isopropanol environment on the deformation characteristics of copoly (acrylonitrile-butadiene-styrene) (ABS) and poly (vinyl chloride) (PVC) have been investigated. Creep tests were performed in tension and torsion both in air and in isopropanol. It was noted that accelerated rates of creep were encountered during the tensile tests in isopropanol as compared with air but no differences were noted during the torsion tests. An explanation is proposed that the greatly increased creep strains encountered in tension result from diffusion of the fluid into the polymer. The rate of diffusion is controlled by changes in the free volume which occur on application of uniaxial tensile stresses. The existence of the fluid molecules in the polymer matrix reduce its local creep resistance and produce swelling, both of which are manifested as increased creep strains. The fact that no effects were noted during torsion tests (where the free volume remains constant) or when an unstressed specimen was immersed in the fluid indicates that no significant absorption occurs at the equilibrium (unstressed) free volume.     

Method for Predicting Creep in Tension and Compression from Bending Tests

It is shown that tensile and compressive creep behavior may be deduced from deflection measurements in creep bending tests on beams of trapezoidal cross section. In the analysis it is assumed that creep strains are proportional to stress and are large relative to elastic strains.