非牛顿流体搅拌流场的数值模拟研究进展

对非牛顿流体搅拌流场数值模拟过程中的控制方程、旋转桨叶的处理以及数值计算方法三个方面进行了综合论述。阐述了广义牛顿流体模型形式简单、计算量低,在非牛顿流体搅拌流场数值模拟过程中应用广泛;黏弹性流体本构方程具有高度的非线性,采用计算流体力学(CFD)方法对其搅拌流场进行数值模拟难度较高,目前仍处于起步阶段;通过合理简化黏弹性流体本构方程以及采用恰当的数值离散方法,有助于在黏弹性流体的搅拌流场数值模拟中取得进展。     

基于Giesekus黏弹性本构的注射成型数值算法研究

针对熔体的黏弹性特征,考虑熔体流动过程中的惯性作用,基于Giesekus模型建立了注射成型中熔体流动的黏弹性理论模型。将黏弹性本构方程整合为含瞬态项、对流项和源项的偏微分方程,基于有限体积法离散,提出了黏弹性本构方程的离散方法。借鉴有限元框架下的黏弹性离散分裂算法（DEVSS）,发展了以有限体积法为基础的黏弹性离散分裂算法（FVM-DEVSS）,开发了三维黏弹性流动的计算程序。用经典充分发展的4∶1收缩流验证方法的有效性,再结合充模流动实验,正确预测了熔体流动前沿、浇口压力及熔接线位置,通过光弹实验结果再次证明了本文方法的有效性。结果表明,本研究所发展的黏弹性算法可以有效表达熔体的黏性和弹性对流动压力的影响,而且能准确预测两股熔体相遇时熔接线的位置及形成过程。此外,本文黏弹性算法有效准确地计算了熔体充模过程中的流动诱导应力。     

多孔SiC中黏弹性流体的流变性数值研究

为研究黏弹性流体在多孔SiC中流变行为,将多孔SiC的骨架建成十四面体结构单元的阵列,利用POLYFLOW计算流体力学软件,黏弹性流体的本构方程采用PTT模型,主要研究黏弹性流体流经多孔SiC的法向应力及剪切应力随松弛时间、多孔介质孔径以及流速变化规律,以及剪切速率的分布特点。黏弹性流体弹性越强,孔道结构对其作用的应力越大,从而使聚合物分子链发生断裂的几率越大。     

聚碳酸酯的应力松弛实验及数据处理分析

以黏弹性力学理论为基础,选用广义Maxwell模型作为聚碳酸酯(PC)黏弹性的力学模型。在120℃温度场下以不同的初始应变进行应力松弛试验,得到应力松弛过程中作用力与时间的实验数据。利用ABAQUS软件拟合得出不同初始应变下的黏弹性模型的prony参数,再结合Origin软件优化得出广义Maxwell黏弹性模型在参考温度为120℃时的普适prony级数参数,来供ABAQUS调用分析,为有限元仿真分析奠定理论基础。     

注塑制品内应力计算的非线性黏弹性本构方程

在聚合物黏弹性理论的基础上,构建了新的注塑制品内应力计算的四元件串联力学模型,并推导了其瞬态黏弹性响应的非线性本构方程,给出了聚合物材料参数弹性模量和黏壶系数的计算公式,并对PS平板注塑制件脱模前的内应力进行了模拟计算。计算结果与固体高聚物的结构和力学性能的相关研究结论相一致,所建计算模型合理可靠。     

PET拉伸吹塑数值模拟采用的本构方程

在PET拉伸吹塑的数值模拟中,采用何种本构方程来反映材料的应力-应变行为对于模拟结果的准确性有着重要的影响.目前所采用的本构方程可分为3类1)将材料的应力-应变行为视为超弹性;2)在数值模拟中采用黏弹性本构方程, 这又可分为微分型与积分型两种;3)采用黏塑性本构方程来描述材料的应力-应变行为.     

弱碱型三元复合驱采出水的流变性变化规律

通过旋转黏度计测试黏弹性和视黏度,研究了三元(碱、表面活性剂、聚合物)复合驱采出水的流变性。结果表明,三元复合驱采出水的黏弹性可用Maxwell线性黏弹性模型描述。其视黏度和黏弹性主要取决于所含聚合物的相对分子质量和含量,并且随聚合物含量的增加而增大。低聚合物含量三元复合驱采出水的视黏度和黏弹性模量之间存在着G=1．6736μ1.8155的关系式。     

O/W膏霜流变性与厚重感关系研究

研究了不同厚重程度指数O/W膏霜的流变学性质,并用非线性共转Jeffreys模型和Maxwell本构方程分别描述其流动曲线和线性黏弹性。结果表明:随着厚重程度指数增大,膏霜的表观黏度、低剪切速率(γ·20 s-1)下的应力值、黏弹性模量等流变学指标均增大。其中,lgη0(共转Jeffreys本构方程中的零剪切黏度)、τ(γ·=10 s-1)、lg G*(γ=1%)与厚重程度指数呈明显的线性关系。流变学指标与厚重程度指数的定量研究可用于预测其厚重程度。     

聚苯乙烯/CO2发泡体系的气泡生长过程模拟

以聚苯乙烯/CO2发泡体系为研究对象,利用细胞模型推导出了基于牛顿流体本构方程、幂律流体本构方程、dewitt黏弹性本构方程3种本构方程的气泡生长数学模型,通过比较分析得出了最适合该发泡体系的气泡生长模型,并研究了熔体弹性和非牛顿性质等物性参数对气泡生长过程的影响。结果表明,dewitt模型能更加准确地反映实际的气泡生长的过程;聚合物熔体弹性在生长初期对气泡生长有明显的促进作用;聚合物熔体的非牛顿性质对于气泡生长全过程都有影响。     

单螺杆挤出过程熔体输送段数值模拟方法

综述了应用于螺杆挤出成型过程熔体输送段数值模拟的各种计算方法，根据挤出过程聚合物流场控制方程，介绍了几种有代表性的聚合物本构关系，包括线性黏弹性和非线性黏弹性本构方程。概述了有限差分法、有限元法、有限体积法和边界元法等数值计算方法的特点和应用范围，并针对聚合物熔体流动模拟中的迭代收敛性和稳定性、耦合和解耦合、高Weissenberg数等问题进行了讨论，指出应该根据研究目的和实际情况选择适宜的本构方程和数值方法。     

Transient modeling of viscosity

Capillary and parallel plate rheological characterization was conducted for a low‐density polyethylene. In contrast with conventional rheological analysis, steady conditions were not assumed. Transient data, with time steps between 0.0001 and 0.2 s, were analyzed with a nonlinear, viscoelastic constitutive model in which the relaxation time was modeled as a function of the applied stress. The fit model explained more than 99% of the observed transient variation in the capillary and parallel plate rheometers. The model coefficients for the capillary and parallel plate were compared directly to conventional linear viscoelastic analysis of the same parallel plate data. The results indicate that the described constitutive model closely predicts the observed viscoelastic behavior of the polymer melt tested in the parallel plate rheometer. Furthermore, the results indicate that the relaxation spectrum modeled with the transient analysis of the capillary rheological data correlate closely to the results predicted by the same transient analysis of parallel plate rheological data. The conclusion is that described constitutive modeling describes the viscoelastic behavior in both capillary and parallel plate rheometers. Moreover, the analysis and results suggest that the viscoelastic behavior of the polymer melt is a significant factor during the rheological characterization and the modeling of the transient response should be taken into consideration during rheological analysis to provide high fidelity models. POLYM. ENG. SCI., 57:1110–1118, 2017. © 2017 Society of Plastics Engineers     

System identification and modeling of viscoelastic behavior from capillary melt rheological data

An investigation was conducted to identify and characterize the relaxation spectrum of polymer melts from transient capillary rheological data. System identification techniques using an iterative prediction‐error minimization (PEM) method were applied to isolate the viscoelastic melt response from the apparatus dynamics. Parameters for linear time invariant (LTI) models of varying complexity were estimated using capillary rheology data across a range of temperatures and shear rates using the principle of time‐temperature superposition. Melt capillary rheology data for polystyrene was found to exhibit viscoleastic behavior. Subsequently, three viscoelastic constitutive models were then implemented and their model coefficients directly fit using optimization techniques. The implemented methods provided useful relaxation behavior from melt capillary rheology data while also explaining much of the residual error in the purely viscous response as traditionally fit to the Cross‐WLF model. POLYM. ENG. SCI., 54:2824–2838, 2014. © 2014 Society of Plastics Engineers     

PE-LD棚膜专用树脂的流变性能研究

选取了几种典型的低密度聚乙烯（PE-LD）棚膜专用树脂,综合转矩流变仪、毛细管流变仪、熔体拉伸流变仪、旋转流变仪等多种流变测量技术研究了其剪切和拉伸流变性能。结果表明,2100和1810D树脂的支化程度更高,加工负荷低,熔体剪切敏感性更高,树脂的加工性能更好;同时,2100树脂的熔体强度更高,应变硬化效应明显,有利于膜泡稳定性;动态流变试验结果显示,长松弛时间分子链提供了熔体强度与应变硬化,宽分布松弛谱赋予了树脂的良好加工性能,2100与1810D树脂的综合性能更佳。     

茂金属聚乙烯蜡对PE共混体系流变行为的影响

用毛细管流变仪研究了茂金属聚乙烯蜡改性聚乙烯共混体系的流变行为，探讨了茂金属聚乙烯蜡用量对共混体系熔体流变行为、熔体黏度、非牛顿指数和流动活化能的影响。结果表明：茂金属聚乙烯蜡对LLDPE／LDPE流动黏度降低明显，增加用量可使黏度逐渐降低；而对MPE／LLDPE／LDPE共混体系流动行为的影响比较复杂，在低剪切应力下黏度随茂金属聚乙烯蜡用量增加而逐渐降低，而在高剪切应力下黏度先增后减；茂金属聚乙烯蜡与MPE／LLDPE／LPDPE的相容性好于LLDPE／LDPE共混体系。     

Finite element modeling of the flow of a rubber compound through an axisymmetric die using the CEF viscoelastic constitutive equation

This work is devoted to the simulation of the flow of a high viscosity NR/SBR rubber compound through the die of a single screw extruder with axisymmetric geometry. An in-house developed computer code based on the use of continuous penalty finite element method was employed. Three constitutive equations including two generalized Newtonian models namely; power-law and Carreau and an explicit viscoelastic model named CEF (Criminale-Ericksen-Fillbey) were used to reflect the rheological behavior of the material. Using the parameters of the rheological models determined by a slit die rheometry technique, the flow of the compound was simulated through the die and results were compared with experimentally measured mass flow rates. It is shown that for high viscosity rubber compounds the use of generalized Newtonian models which do not take the normal stress in simple shear flow into consideration gives rise to significant errors in prediction of mass flow rates. On the other hand, comparing the simulations results using the CEF equation with experimental data revealed that this model is the best compromise between generalized Newtonian and full viscoelastic models which need high computational costs and effort. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Experimental investigation of the influence of molecular weight distribution on the rheological properties of polypropylene melts

An experimental study of steady shear and elongational flow Theological properties of a series of polypropylene melts of varying molecular weight and distribution is reported. Broadening the molecular weight distribution increases the non-Newtonian character of the shear viscosity function and increases the principal normal stress differences at fixed shear stress. The behavior is compared to earlier rheological property-molecular weight studies. Correlations are developed for these properties in terms of molecular structure. Elongational flow studies indicate that for commercial and broader molecular weight distribution samples, ready failure by neck development occurs and the elongational viscosity appears to decrease with increasing elongation rate. For narrower molecular weight distribution samples, the elongational viscosity is an increasing function of elongation rate, The implication of these experimental results to viscoelastic fluid constitutive equations and polymer melt processing is developed.     

高熔体强度聚丙烯/低密度聚乙烯共混体系的挤出发泡行为研究

利用熔体流动速率测试仪和转矩流变仪对不同比例的高熔体强度聚丙烯(HMSPP)/低密度聚乙烯(PELD)共混体系的流变行为进行研究,并对共混体系的流变数据进行分析.随后采用超临界CO2作为发泡剂进行了HMSPP/PE-LD共混体系的挤出发泡研究,并通过真密度计和扫描电子显微镜表征了发泡材料的表观密度和泡体结构参数.结果表...     

Melt Rheological Properties of Silver-Powder-Filled Polypropylene Composites

The melt rheological properties of titanate coupling-agent-treated particulate silver powder (varying from 0 to 5.6 vol% of Ag) were investigated. The effect of filler concentration on shear stress, shear rate, melt viscosity, and melt elasticity parameters were determined by using a piston-type capillary rheometer. The study shows that the materials follow a power law in viscous behavior over the entire range of shear rates and temperatures investigated. The melt viscosity decreases with filler content up to 4.1% and increases with a further increase in filler content. Interestingly, the viscosity of the composition was lower than that of unfilled polypropylene. The melt elasticity decreases with an increase in Ag content in the composites up to 4.1%; beyond that, it increases. The effect of temperature on the viscoelastic properties of filled polypropylene was also investigated.     

Non-linear viscoelastic behavior and damping factor of polypropylene/clay nanocomposites

The non-linear viscoelastic properties of pure polypropylene and its clay nanocomposites are studied to establish structure–property relationship in conjunction with clay concentrations. First, flow birefringence is performed through a slit-die to obtain centerline principal stress difference during elongational flow for clay nanocomposites. The centerline stress profile of clay nanocomposite reveals additional viscoelastic nature even at low silicate concentrations, while similar short-time chain relaxation is observed. The effects of higher clay concentrations are further examined during the simple shearing flow to consider damping properties of the clay nanocomposites. The step strain, dynamic shear and steady shear are performed. All the samples show time-strain separable melt flow behavior adequately demonstrated through Wagner’s exponential damping function. The damping coefficient is found to be strongly dependent on clay percentage revealing viscoelastic differences therein. We have also used a time-strain separable Kaye-Bernstein Kearsley Zapas (K-BKZ) type constitutive equation to predict steady shear stress. The suggested constitutive model satisfies simple shear at lower fractions of clay while the damping function behaves similar to pure polymer thought to result from the absence of filler–filler interactions and chain length degradation. The unusual rheological behavior for maximum clay concentration studied is explained on experimental as well as theoretical basis. Thus, the results of this investigation would improve the theoretical understanding of possible molecular orientations at different clay concentrations during elongational and shearing flows.     

方柱绕流中聚乙烯熔体流变行为的数值模拟

采用了DCPP和S-MDCPP两种模型分别描述低密度聚乙烯熔体的本构行为。在迭代分步算法中引入了改进的有限增量微积分(FIC)法,并采用离散的弹性黏性应力分裂技术(DEVSS)/迎风流线(SU)法解决黏弹性流动分析中的对流占优问题。讨论了S-MDCPP模型预测的速度、压力及主链拉伸分布随Weissenberg(Wi)数的变化。结果表明,两种模型预测的速度、主应力差等色条纹和主链拉伸分布吻合较好;随Wi的增大,速度及压力均增大。