ABS树脂拉伸性能及形变机理的研究

研究了丙烯腈丁二烯苯乙烯共聚物（ABS）树脂在不同温度和不同拉伸速率时的拉伸行为以及物理老化对其拉伸行为的影响。结果表明,屈服强度随测试温度的升高而下降,断裂伸长率并不随着测试温度的升高而提高,直到测试温度升高到接近ABS树脂塑料相的玻璃化转变温度时,断裂伸长率才显著提高;断裂伸长率随拉伸速率的增加而降低,在不同的拉伸速率下,ABS的形变区内均可观察到银纹现象;在较高的拉伸速率下,形成的银纹数量较多,但银纹较短,银纹的扩展得到了有效抑制;ABS树脂经物理老化后断裂伸长率明显降低,银纹数量增加并出现了空洞成串现象。     

聚合物溶液流变曲线及粘温特性研究

用长庆油田北三区处理后清水、聚丙烯酰胺配制了聚合物母液和目的液,聚合物母液浓度5000mg/L、目的液浓度2000mg/L,测量温度为10~60℃,剪切速率为1~100s~(-1),考察了剪切速率、温度对不同浓度聚合物的流变性、粘度影响。结果表明,聚合物溶液的粘度随剪切速率的增大不断降低,同一剪切速率下聚合物溶液的表观粘度随温度的升高也有所下降,随着测量温度的升高,聚合物溶液的屈服应力逐渐降低,稠度系数K逐渐增大而流变行为指数逐渐减小,在实际测量温度范围内,聚合物溶液属于非牛顿流体,体现出典型的屈服-假塑性流体特性,剪切速率对聚合物溶液的粘度值影响很大,测量温度对粘度值的影响较小。     

基于DIC系统的PE-HD力学性能

基于数字图像相关法(DIC)研究了加载速率和汽油浸泡时间对高密度聚乙烯(PE–HD)材料拉伸性能的影响。实验表明,PE–HD材料的屈服应力随加载速率的增加而增加,但随加载速率的增大,其对屈服应力的影响逐渐减小;断裂伸长率随加载速率的增加明显减小;屈服应变不随加载速率的改变而改变;计算出各加载速率下材料的拉伸弹性模量大小。经汽油处理过的PE–HD屈服应力和拉伸弹性模量随浸泡时间快速下降随后趋于稳定,材料的强度降低到一个稳定的值。     

熔体拉伸对聚苯乙烯屈服行为影响的研究

作为典型的玻璃状聚合物，聚苯乙烯在室温下通常表现出脆性。通过熔体拉伸法可以诱导聚苯乙烯在室温下发生脆韧转变。研究聚苯乙烯的脆韧转变行为和屈服行为是研究玻璃状聚合物大形变机理的重要工作之一。采用熔体拉伸法在不同的熔体拉伸应变下制备了聚苯乙烯薄膜，基于Eyring屈服活化理论计算了熔体拉伸聚苯乙烯薄膜在不同温度下的屈服活化能。结果表明，随着熔体拉伸应变的增加，薄膜的屈服应力及屈服活化能快速下降，从而赋予了聚苯乙烯在室温甚至更低的温度环境内发生拉伸屈服的能力。     

稠油乳状液屈服特性及环道启动压力预测

针对海上平台稠油管线停输置换、再启动难题,以旅大稠油为研究对象,利用Rheolab QC流变仪测量系统剖析稠油及其乳状液启动过程与初始阶段力学响应特性,讨论含水率、启动温度、静置时间与恒定剪切速率对启动屈服应力的影响作用,自主研制并加工搭建了室内小型再启动环道实验装置,测量与验证再启动压力理论预测值可靠性。实验结果表明：稠油乳状液启动过程可划分为屈服、衰减和平衡3个阶段,启动屈服应力均在反相点附近达到最大值,随着启动温度升高而降低,随恒定剪切速率增大而增大;适当增大启动流量可缩短管线启动时间,但同时也增大了启动压力;基于启动屈服应力的启动压力预测值是环道实验装置测量值的2～3倍,而基于平衡剪切应力的启动压力预测值与实测值吻合较好,平均相对误差为4.5%。     

外界环境因素对热塑性橡塑共混开孔材料的影响Ⅱ橡塑共混开孔材料的蠕变行为

研究了退火温度和时间及退火后放置时间对橡塑开孔材料透水速率的影响。结果表明：开孔材料透水速率随退火温度的升高而下降，退火温度越高，下降的幅度越大；同一退火温度下，透水速率随退火后放置时间的增长而降低，放置时间越长下降的幅度越大；透水速率随退火时间的增长而下降，退火时间越长，下降幅度越大。     

剪切速率和温度对低水胶比水泥浆流变性能的影响

水泥浆体的流变性能不仅与材料本身有关,还受环境及外部作用影响。本文针对水泥基材料实际工程中存在的主要外部影响因素,即剪切作用与环境温度,研究了两者对低水胶比水泥浆流变性能的耦合作用。结果表明:水泥浆体在剪切过程中的流变行为与所施加的预剪切有关,水泥浆体的屈服应力随预剪切速率的增大而减小,剪切增稠的程度随预剪切速率的增大而增大;温度升高,水泥颗粒对减水剂的吸附量增加,浆体在不同剪切速率下的平衡表观黏度减小;温度和剪切速率对水泥浆平衡表观黏度的影响具有耦合效应,剪切速率越高,温度的影响越小,反之亦然,并建立了不同温度和剪切速率下平衡表观黏度的数学关系。     

汽车内饰件模外装饰用PMMA的力学性能

为研究汽车内饰件模外装饰材料聚甲基丙烯酸甲酯(PMMA)的力学性能,对PMMA膜材分别在2.5 mm/min(0.001 667 s-1),5 mm/min(0.003 333 s-1)和10 mm/min(0.006 667 s-1)不同拉伸速率下进行高温[90℃(363K),105℃(378 K)和115℃(388 K)]单向拉伸实验,得到了不同条件下的应力–应变曲线。实验结果表明,当加热温度相同时,随着应变速率的增大,PMMA的应力、延伸率和屈服应力也逐渐提升。当应变速率一致时,其屈服强度与应力随着温度的升高而逐渐变小。     

热水浴拉伸对聚丙烯腈初生纤维结构和性能的影响

研究了聚丙烯腈(PAN)初生纤维在热水浴拉伸过程中超分子结构和力学性能的变化。结果表明:PAN初生纤维中的内应力随拉伸温度的升高而减小,随拉伸速率和拉伸倍数的提高而增大;初生纤维在热水浴中的玻璃化转变温度约为80℃,当水浴温度低于和高于80℃时,纤维分别发生冷拉和高弹形变;PAN初生纤维的结晶度和晶区取向度随拉伸温度的升高先增大后减小,随拉伸速率和拉伸倍数的升高而增大。     

熔融纺丝法研究LDPE的拉伸流变性能

采用熔融纺丝法研究了低密度聚乙烯(LDPE)熔体的拉伸流变性能。LDPE熔体强度随温度升高而下降;适当降低拉伸黏度可提高熔体的可拉伸性;随拉伸应变速率升高拉伸应力上升,而拉伸黏度下降;拉伸应力和拉伸黏度都随温度的升高呈下降趋势;提高挤出速率可得到较低的拉伸应力和拉伸黏度。     

Tensile yield in phenolphthalein polyether ketone

Uniaxial tension tests to the yield point were performed on phenolphthalein polyether ketone (PEK-C) from room temperature to near the glass transition temperature (T_g) at a constant rate of 0.02 min^?1. At room temperature, some measurements were also made at strain rates from 0.002 min^?1 to 2 min^?1. Yield stress was a linear function of temperature and log strain rate. The temperature and the strain rate dependence of yield stress could be modeled using Eyring theory. Yield energy was found to be a linear function of temperature. Young's modulus, yield strain, elastic strain, and plastic strain all decreased with temperature. © 1994 John Wiley & Sons, Inc.     

Effect of temperature on the compressive stress-strain properties of polystyrene

The compressive stress-strain behavior of a commercial polystyrene has been studied and the effect of deformation temperature on modulus, yield stress, percent yield strain and yield energy was determined. Yield energy is the only one of these parameters that is linear with temperature in the ductile region. A change in the mode of failure from ductile to brittle occurs between 5–30°C at a strain rate of O.1/in./in./min. At all temperatures studied, the yield or fracture stress varied linearly with the rate of deformation for strain rates ranging from 0.1 to 1.0 in./in./min. The yield data as a function of temperature were analyzed via a rate expression modified to incorporate the Coulomb-Navier yield criterion, Activation energy was found to be a function of deformation temperature with a change in slope occurring near the β transition. Activation volume increased linearly with deformation temperature, for the range studied. Agreement of dynamic mechanical and yield activation energies imply that the type of motion and the height of the energy barrier are similar for both. However, an increase in activation volume for stressed vs unstressed conditions suggests that a greater number of chain segments move as a result of stress biasing. Also the increase of both activation volume and activation energy with temperature implies that the correlated length of chain movement increases as temperature is increased. Similar to activation energy, yield stress exhibits a change in temperature dependence near the β transition. Data on other glassy polymers suggest that the highest temperature sub-T_g, transition is related to the change in the temperature dependence of yield stress.     

A formulation of the cooperative model for the yield stress of amorphous polymers for a wide range of strain rates and temperatures

The mechanical response of solid amorphous polymers is strongly dependent on the temperature and strain rate. More specifically, the yield stress increases dramatically for the low temperatures as well as for the high strain rates. To describe this behavior, we propose a new formulation of the cooperative model of Fotheringham and Cherry where the final mathematical form of the model is derived according to the strain rate/temperature superposition principle of the yield stress. According to our development, the yield behavior can be correlated to the secondary relaxation and we propose an extension of the model to temperatures above the glass transition temperature. For a wide range of temperatures and strain rates (including the impact strain rates), the predicted compressive yield stresses obtained for the polycarbonate (PC) and the polymethylmethacrylate (PMMA) are in excellent agreement with the experimental data found in the literature.     

Tensile yield in poly(chlorotrifluoroethylene) and poly(vinylidene fluoride)

Uniaxial tension tests to the yield point were performed on poly(chlorotrifluoroethylene) (PCTFE) and poly(vinylidene fluoride) (PVF2) from room temperature to near the melting point at a strain rate of 2 min^?1. At room temperature and at least two elevated temperatures, measurements were also made at strain rates from 0.02 to 8 min^?1. The properties of these polymers were found to be similar to those of other semicrystalline polymers. In the absence of other transitions, yield energy was found to be a linear function of temperature extrapolating to zero near the melting temperature. The ratio of thermal to mechanical energy to produce yielding is smaller than for glassy polymers. Yield stress is a linear function of log strain rate. The ratio of yield stress to (initial) Young's modulus is about 0.03 at room temperature for both polymers. Yield stress is a linear function of unstrained volume. Yield strain, elastic, and plastic strain all initially increase with temperature, but PCTFE shows a decrease with temperature starting at about 100°C, thus behaving like a glassy amorphous polymer in this region.     

Estimating time and temperature dependent yield stress of cement paste using oscillatory rheology and genetic algorithms

A controlled shear stress–shear rate rheometer was used to determine the viscoelastic behavior of cement paste incorporating various superplasticizers and subjected to prolonged mixing at high temperature. At a low applied shear stress range, the oscillatory shear strain/stress curve of cement paste was characteristic of a linear elastic solid; while the higher stress range was characteristic of a viscous liquid exhibiting a linear strain increase with increasing applied shear stress. The transition from solid-like to liquid-like behavior occurred over a very narrow stress increment. This transition stress corresponded to the yield stress parameter estimated from conventional flow curves using the Bingham model. The yield stress from oscillatory shear stress tests was estimated using the intersection between the viscous part of the oscillatory shear strain/stress curve and the oscillatory shear stress axis. In this study, equations describing the variation of shear strain versus shear stress beyond the solid–fluid transition for cement pastes incorporating various superplasticizers at different ambient temperatures and mixing times were developed using genetic algorithms (GA). The yield stress of cement pastes was subsequently predicted using the developed equations by calculating the stress corresponding to zero strain. A sensitivity analysis was performed to evaluate the effects of the mixing time, ambient temperature, and superplasticizer dosage on the calculated yield stress. It is shown that the computed yield stress values compare well with corresponding experimental data measured using oscillatory rheology.     

Thermal and strain rate sensitive compressive behavior of polycarbonate polymer - experimental and constitutive analysis

The mechanical behavior of polycarbonate (PC) polymer was investigated under the effect of various temperatures and strain rates. Characterization of polymer was carried out through uniaxial compression tests and split Hopkinson pressure bar (SHPB) dynamic tests for low and high strain rates respectively. The experiments were performed for strain rates varying from 10 ^?3 to 10³ and temperature range of 213 to 393 K. By conducting these experiments, the true stress–strain (SS) curves were obtained at different temperatures and strain rates. The results from experiments reveal that the stress–strain behavior of polycarbonates is different at lower and higher strain rates. At higher strain rate, the polymer yields at higher yield stress compared to that at low strain rate. At lower strain rate, the yield stress of the polymer increases with the increase in strain rate while it decreases significantly with the increase of temperature. Likewise, initial elastic modulus, yield and flow stress increase with the increase in strain rate while decreases with the increase in temperature. The yield stress increases significantly for low temperature and higher strain rates. On the basis of experimental findings, a phenomenological constitutive model was employed to capture the mechanical behavior of polymer under temperature and loading rate variations. The model predicted the yield stress of polymer at varying strain rate and temperature also it successfully predicted the compressive behavior of polymer under entire range of deformation.     

模外装饰贴膜材料力学性能研究

以对聚甲基丙烯酸甲酯（PMMA）为膜外装饰贴膜材料,对其进行不同温度和不同拉伸速度的高温单向拉伸实验,得到相应条件下PMMA的真实应力真实应变曲线,分别计算出不同温度和不同应变速率的DSGZ本构模型系数,将DSGZ模型的理论预测曲线与其拉伸实验数据曲线进行对比分析。结果表明,在同一温度下,随着应变速率的增大,其真实应力、拉伸比和屈服强度也相应地增大;在同一应变速率下,随着温度的逐渐升高,PMMA的应变软化和屈服现象随之减弱直至消失,其真实应力也明显减小;DSGZ模型的预测曲线与其实验数据曲线基本一致,DSGZ能够较真实地反映PMMA的力学性能。     

Time and temperature effects on the tensile yield properties of polypropylene

Tensile tests were made on polypropylene films as a function of aging temperature from 80 to 130°C at a strain rate of 5 cm min^-1. Polypropylene films aged at 60 and 100°C and at time intervals up to 180 min were also stretched at the same strain rate. The yield stress and initial modulus were found to be linear functions of temperature, extrapolating to a zero value close to the thermodynamic melting point of the polymer (170°C). The work of yield, the plastic and yield strains also decreased with increase in aging temperature but the elastic strain increased. The plastic strain, yield strain, yield stress, and initial modulus for the 60°C aged film had larger values than the corresponding values for the 100°C aged film at equivalent time intervals and all properties decreased with increasing log time of aging. These decreases in properties were explained in terms of decrease in the density (crystallinity) of aged PP films. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 625–633, 1997     

Dynamical Flow Properties of Single Crystals of Sapphire, I

The tensile deformation of sapphire was studied as a function of the temperature and of the strain rate. The ranges of the two variables were approximately 1200° to 1700°C and 10⁻³ to 10⁻¹in. per in. per minute. The work showed the existence of a relatively sharp temperature transition between completely brittle fracture and massive plastic flow, the specific transition temperature being sensitively related to the strain rate. For the limits of the rate range used, the transition temperature increased from approximately 1270° to 1520°c. In going through a range of only a few degrees of temperature near the transition, it was possible to obtain either no plastic flow on the low-temperature side or a relatively large amount of the order of a 100% extension on the high-temperature side. The stress-strain relation for plastic flow was found to be characterized by a pronounced yield-point drop; i.e., the stress required to initiate macroscopic flow was approximately double that required for subsequent flow. The magnitudes of both the upper and lower yield stresses were temperature sensitive and both decreased approximately exponentially with increasing temperature for a given strain rate. An inverse dependency of a similar kind was found for the effect of strain rate under conditions of isothermal testing. On the other hand, the fracture stress before yielding was found to be essentially independent of both temperature and strain rate, lying in a scatter band of approximately 16,000 to 20,000 psi. As the testing temperature at a given strain rate was lowered, the plastic yield stress therefore rose sharply. The transition temperature between ductile and brittle behavior was interpreted to correspond to the temperature at which the upper yield stress equaled the fracture stress. Since the lower yield stress was only half the upper yield stress, extensive flow then became possible whenever the transition temperature for yielding was exceeded.     

Rate-dependence of yielding in ethylene-methacrylic acid copolymers

It is well known that reducing the crystal thickness of polyethylene, by copolymerization with an α-olefin, decreases the yield stress. By contrast, incorporation of methacrylic acid (MAA) - also a noncrystallizable comonomer - results in a marked increase of the yield stress at room temperature at typical strain rates. We show that, in addition to crystal plasticity, one must consider the active mechanical relaxations to understand this phenomenon. For ethylene-methacrylic acid copolymers, the α and β relaxations are important over the range of conditions probed in this study, and the increase in the β relaxation (glass transition) temperature with MAA content is identified as the source of this peculiar behavior. The yield stress of these materials is adequately described by a model combining thermal nucleation of dislocations in the crystals with a Ree-Eyring dependence for yielding in the amorphous phase, all with physically reasonable parameter values. Yield stress master curves may be created from data taken at various temperatures and strain rates, and are presented herein for low-density polyethylene and five ethylene-methacrylic acid copolymers of varying MAA content.