短纤维-弹性体复合材料的注射充模

对短纤维-聚氨酯弹性体复合材料的注射充模及纤维取向分布进行了数值模拟和实验研究。结果表明,纤维取向分布主要取决于模腔几何形状、纤维含量和注射工艺条件等因素。在薄壁型腔的扩张流中,短纤维趋于与流线方向垂直,而在剪切流和收敛流中趋于与流线方向一致。纤维取向分布实验结果与数值模拟结果较一致,表明理论模型有一定的实用价值。     

三维取向短纤维增强复合材料弹性模量的计算

基于单取向纤维增强复合材料的力学性能计算模型,借助于纤维取向分布函数及坐标转换,建立了三维取向短纤维增强复合材料弹性模量的数值计算模型。按该模型对短纤维增强树脂基复合材料的弹性模量进行计算,将其结果与同类材料的实验结果比较验证。结果表明,该模型的预测具有较好的准确性。     

短纤维-弹性体复合材料的注射充模Ⅱ.数值模拟和实验研究

对短纤维－聚氨酯弹性体复合材料的注射充模及纤维取向分布进行了数值模拟和实验研究。结果表明,纤维取向分布主要取决于模腔几何形状,纤维含量和注射工艺条件等因素,在薄壁型腔的扩张流中,短纤维趋于与流线方向垂直,而在剪切流和收敛流中趋于与流线方向一致,纤维取向分布实验结果与数值模拟结果较一致,表明理论模型有一定的实用价值。     

短纤维-弹性体复合材料的注射充模I．数学物理模型的建立

研究了短纤维－弹性体复合材料注射充模过程中,流动前锋和上的喷泉效应,固化层及纤维用量与纤维之间相互作用等的影响,建立了薄壁拉伸试样型腔中短纤维－弹性体复合材料注射充模过程及其纤维取向分布的数学物理模型。     

纤维增强塑料的充模流动和纤维取向的耦合仿真模型

分析充模流动、纤维取向耦合仿真的特点,在此基础上提出充模流动、纤维取向耦合仿真模型,可对充填和后充填阶段的可压缩流体的非对称流动,以及由于熔体流动引起的三维纤维取向行为进行统一建模,并且两者相互耦合,在耦合程度上考虑了由于增强纤维存在并且取向引起的熔体流动类型、流变学性质和本构方程的变化.     

短纤维—热塑性聚氨酯弹性体注射充模过程的研究进展

介绍了短纤维－热塑性聚氨酯弹性体（ＳＦ－ＴＰＵ）注射充模过程国内外的研究进展,ＳＦ－ＴＰＵ注射充模过程与通常高聚物有许多相似之处,更有其不同特点。国内外的研究者们对其注射充填过程中的传热、流动、纤维取向与加工条件、模腔几何参数之间的关系进行了研究,但纤维与流体的相互作用、前锋流对纤维取向的影响等,还须进一步研究。     

长方体状注射模腔内纤维取向分布模拟计算

通过数值求解长方体塑料注射模腔中纤维运动的Fokker-Planck方程,得到纤维在塑料熔体中三维取向张量.计算结果表明:模腔界面附近纤维主要沿流动方向取向,模腔对称的中心面附近主要发生厚度方向的取向,而且3个方向取向中,流动方向的纤维取向度最高.此外,考虑了影响纤维取向的工艺因素,如熔体入口温度和模腔壁温、充模时间.其中,充模时间的影响较显著.     

层叠单元流道对纤维取向作用的数值模拟

基于广义非牛顿流体本构方程,建立了纤维增强聚合物三维层叠单元流道注塑成型充填阶段数学模型,采用Moldex3D对短纤维增强复合材料在层叠单元流道中的注塑流动过程进行模拟,研究了层叠单元流道对纤维流动取向的影响。结果表明:入口处的纤维从开放领域进入较窄领域,取向呈随机分布状态;进入流道后,表层纤维取向度迅速提高;在接近流道出口处,纤维取向度降低,在出口截面的两侧和中间部分均出现了随机取向纤维。     

短纤维增强橡胶材料的力学模型

在材料剪切滞后分析与随机顺序吸收法的基础上建立了短纤维增强橡胶材料(SFRC)的理论模型与有限元模型。通过简化将SFRC模型中的三维随机取向纤维降为二维取向,对短纤维增强阻尼材料的弹性模型进行计算与拟合。结果表明,随纤维体积分数的增大,SFRC的模量逐渐增加。当纤维体积分数为2.00%时,材料的弹性模量增加了约1倍,与试验值基本相符合。有限元分析结果与试验结果相吻合,表明该模型在进行SFRC的力学行为分析时具有一定的真实性。当材料应变在300%以内时,有限元模型可以对SFRC的力学行为进行比较准确的描述。     

注射成型纤维取向模拟及实验验证

通过实验分析了短纤维增强复合材料注射成型标准试样中的纤维取向分布,并与Moldflow模拟结果进行了对比.结果表明,注塑试样标定段具有分层取向结构,表层沿流动方向取向强烈,过渡层取向程度下降,但仍为平面取向,芯层则表现为三维取向分布.Moldflow模拟结果与实验结果对比表明,模拟结果高估了芯层的取向程度.     

Rheological behavior and fiber orientation in slit flow of fiber reinforced thermoplastics

The flow behavior and fiber orientation in slit flow of a short fiber reinforced thermoplastic composite melt are investigated. A slit die with adjustable gap and interchangeable entrance geometries was designed and built. The slit die is fed by a single screw extruder. The bulk viscosity is calculated from the axial pressure profiles measured using three flush mounted pressure transducers. The effect of entrance geometry and gap dimensions on the fiber orientation and bulk flow behavior is specifically considered. A skin-core composite fiber orientation is observed in the thickness direction. Fibers are oriented in the flow direction and parallel to the walls in the skin region irrespective of the entrance geometry. Different fiber orientation distributions in the core region can be realized by using different entrance geometries. However, the changes in the core fiber orientation are not fully reflected by the measured viscosities, due to highly oriented skin layer. Exit pressures obtained by extrapolation of linear pressure profiles are found to be all positive, but dependent on the die geometry and entrance conditions, even for the unfilled melts.     

高纤维含量的短切碳纤维增强尼龙流变行为研究

以40%高纤维含量的短切碳纤维增强尼龙(PA66/SCF(40%))复合材料为研究对象,采用高压毛细管流变仪对其挤出料粒进行稳态流变试验,并采用扫描电子显微镜(SEM)观察其注塑试样拉伸断面表观形貌,深入研究了高纤维含量下短切碳纤维增强尼龙的流变行为。结果表明,随着表观剪切速率增加,材料挤出过程中总压力降不断增加;随着温度增加,总压力降逐渐减小;PA66/SCF(40%)复合材料为假塑性流体,存在剪切变稀行为,在较高剪切速率下,纤维沿流动方向发生取向;材料挤出胀大比与弹性回复有关,挤出胀大比随剪切速率增加而增加,随温度增加而减小。     

微型气液固三相等温微分浆态床反应器的优化

针对气液固三相浆态床催化反应中,传递、反应、催化剂的原位表征均比较复杂的问题,为了有利于气、固相均匀分散于液相和反应温度在反应器中实现等温,通过对气液固三相反应工艺特性和反应器性能要求的分析,对微型气液固三相浆态床反应器进行了优化。根据微型浆态床对气液固三相反应分析的要求,采用图像法研究了分布器为G1、G2、G3,砂板直径为2、2.5、3 cm反应器中的流体力学性能特征,考察了气体流速、温度、反应器直径及气体分布器对气含率、气泡尺寸、气泡上升速率以及气泡分布的影响,并进行流体动力学模拟计算,确定了微型浆态床反应器的直径为2 cm,气体分布器为G3砂板的反应器结构,该反应器可以应用于反应过程中间态及液体产物生成过程的测试。     

Hydrostatically extruded glass fiber reinforced polyoxymethylene. II: Modeling the elastic properties

This paper describes an investigation into modeling the elastic properties of hydrostatically extruded short glass fiber reinforced polyoxymethylene (POM). The starting material for the extrusion was randomly arranged short glass fibers (25 wt%, average length 150 μm) in an isotropic POM matrix. Extrusion was carried out through a reducing conical die at 15°C below the melting point of the matrix phase (hence the composite was extruded in the solid state), such that after extrusion, preferential alignment along the extrusion direction was developed for both the fibers and for the crystalline fraction of the polymer matrix. The elastic properties of samples, made over a range of extrusion ratios, were measured using the ultrasonic immersion method, a technique that allows a complete set of elastic constants to be determined for a composite. Theoretical predictions for the elastic properties of the oriented extrudates were generated by combining a modification to the theory of Wilczynski to allow for the fibers' being surrounded by an oriented matrix phase, together with the aggregate model of Ward to model the effects of partial orientation of the fiber oriented matrix units.     

Short fiber reinforced thermoplastics. I. Rheological properties of glass fiber reinforced Noryl

An experimental study on the flow behavior of glass fiber reinforced Noryl (a commercial poly(phenyleneoxide)/polystyrene blend) using a capillary rheometer is described. The effect of fiber concentration on shear viscosity and die swell was studied at various temperatures. Breakage of glass fibers during flow through the rheometer is discussed; it was found that the average fiber length (about 230 μm) was not significiantly altered, except at the highest shear rate (575 s⁻¹) studied. The incorporation of short fibers into thermoplastic polymer melts increases their viscosity without changing the basic rheological character-shear rate dependency. No discernible viscosity changes were measured by incorporating 10 weight percent fibers, and upon further increase of fiber concentration from 20 to 30 weight percent no appreciable increase in viscosity was noted. It is shown that short glass fibers cause a large reduction in extrudate swell. The presence of voids and fiber orientation contribute to the decrease of the die swell, an effect greater than expected from volumetric considerations alone.     

The mechanical properties of oriented discontinuous fiber-reinforced thermoplastics. I. Unidirectional fiber orientation

The mechanical properties of a series of thermoplastics reinforced with unidirectionally oriented short fibers are reported. Both organic and inorganic fiber reinforcements were used in fiber volume fractions of 0.10 to 0.50. A number of these composites were found to have excellent strength and stiffness properties combined with good toughness and low density. The dependence of composite properties on the properties of the constituent materials is discussed. Fiber efficiency factors for strength and modulus are presented and models for predicting composite mechanical behavior are reviewed.     

Tribological behavior of short‐fiber‐reinforced polyimide composites under dry‐sliding and water‐lubricated conditions

Polyimide composites reinforced with short‐cut fibers such as carbon, glass, and quartz fibers were fabricated by the polymerization of monomer reactants process. The mechanical properties of the composites with different fiber contents were evaluated. The friction and wear properties of the polyimide and its composites were investigated under dry‐sliding and water‐lubricated conditions. The results indicated that the short‐carbon‐fiber‐reinforced polyimide composites had better tensile and flexural strengths and improved tribological properties in comparison with glass‐fiber‐ and quartz‐fiber‐reinforced polyimide composites. The incorporation of short carbon fibers into the polyimide contributed to decreases in the friction coefficient and wear rate under both dry and water‐lubricated conditions and especially under water lubrication because of the boundary lubrication effect of water. The polyimide and its composites were characterized by plastic deformation, microcracking, and spalling under both dry and water‐lubricated conditions, which were significantly abated under the water‐lubricated condition. The glass and quartz fibers were easily abraded and broken; the broken fibers transferred to the mating metal surface and increased the surface roughness of mating stainless steel, which led to the wear rate increasing for the glass‐fiber‐ and quartz‐fiber‐reinforced polyimide composites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Description and modeling of fiber orientation in injection molding of fiber reinforced thermoplastics

As mechanical properties of short fiber reinforced thermoplastic injected components depend on flow induced fiber orientation, there is considerable interest in validating and improving models which link the flow field and fiber orientations to mechanical properties. The present paper concerns firstly the observation and quantification of fiber orientation in a rectangular plaque with adjustable thickness and molded with 30 and 50 wt% short fiber reinforced polyarylamide. An automated 2D optical technique has been used to determine fiber orientations. A classical skin (with orientation parallel to the flow)-core (with orientation perpendicular) structure is observed for thick plaques (thickness greater than 3 mm) but the core region is fragmentary for thickness less than 1.7 mm. It is shown that the gate design and different levels of fiber interactions, due to different fiber concentrations, are responsible for these observations. Secondly, computer simulations of flow and fiber orientation are shown. The agreement with the actual data is good, except in the case of the core for thin plaques. The limitations that have to be resolved come not only from the standard fiber orientation equations, but also from the flow kinematics computation.     

Modulus of short carbon and glass fiber reinforced composites

A theoretical model for a short fiber reinforced composite is proposed. The composite is assumed to consist of an aggregate of sub-units, each sub-unit possessing the elastic properties of a reinforced composite in which the fibers are continuous and fully aligned. The elastic constants of a partially oriented composite are then calculated by the Voigt and Reuss averaging procedures, giving upper and lower bounds respectively for the composite modulus. Comparison is made with experimental data for such composites. The measured modulus of glass and carbon fiber composites is found to be given by the Reuss or lower bound, to a good approximation compared with the difference between the bounds, for fiber orientations ranging from almost isotropic to highly aligned.