注塑成型FRP的力学性能预测的数值模拟

纤维增强复合材料的力学性能和热物理性能强烈地依赖于纤维的取向状态，在注射成型过程中，纤维最终的取向状态依赖于充填过程的速度场，因此最终的产品性质依赖于成型的详细过程。研究发现，注塑成型制品的结构呈层状分布，层的数目依赖于模具几何和成型条件，不过大多数的结构在成型表面为沿流动方向取向，而在中心层为横向排列，有时在制件表面还有一层薄的介于二者之间排列的取向层。本文主要给出在两个简单模型中的纤维取向预测的理论和数值方法，这两个模型分别为：中心浇口圆盘和边浇口长条。     

碳纤维复合材料的注塑成型数学模拟研究

采用Moldflow软件对碳纤维复合材料的注塑成型过程进行模拟,并结合Folgar-tucker模型对脱模后的注塑成型碳纤维复合材料的残余应力、温度、弹性模量、泊松比和热膨胀系数等进行模拟。结果表明,纤维不同位置的取向张量不同,浇口位置和纤维末端的取向程度低于中间部分;无论浇口位置如何改变,纤维取向都会与熔体流动方向趋于相同;皮层的取向张量不会因为浇口位置改变而发生明显变化;碳纤维复合材料的边部区域的残余应力和温度与芯部不同;弹性模量E1和弹性模量G12分布与碳纤维取向呈正相关性;碳纤维取向程度对泊松比和热膨胀系数的影响较小,碳纤维复合材料各区域的泊松比和热膨胀系数分布相对均匀。     

注塑流动过程中的纤维定向计算机模拟

本文基于Hele-Show流动,采用Dinh定向计算模型,运用分层计算方法模拟中等浓度短纤维增强塑料在注塑流动成型过程中纤维的取向状态,以多层的定向描述了制品截面内的整体定向情况。     

电动车箱盖纤维填充取向与浇口位置关系分析

通过Moldflow软件对玻璃纤维增强聚丙烯（PP）复合材料电动车箱盖注射成型塑件的成型过程进行模拟分析;第一步按照常规方法找到最佳浇口位置,确定对比参数, 得到平均玻璃纤维取向值为0.9956;第二步再通过设置不同的浇口位置,得到玻璃纤维在制品中的最佳取向值,最佳浇口位置的平均玻璃纤维取向值为0.9992;根据此最佳浇口位置所得到的拉伸模量云图和泊松比云图的数值可以进一步验证此浇口位置为最佳浇口位置。结果表明,常规方法所分析的最佳浇口位置,不一定是最佳浇口位置,要通过不同的条件进行验证才能得到最佳的结果。     

注射成型纤维增强试样的机械性能模拟

采用Moldflow软件对注射成型纤维增强热塑性塑料的拉伸试样进行模拟研究.详细分析了注塑成型拉伸试样的纤维取向结构及由此引起的机械性能变化.分析表明:试样标距位置的纤维平均取向较好、皮芯结构不明显,标距外的两端部及两过渡位置的纤维平均取向不佳、皮芯结构较为明显;试样的物理性能参数受到取向影响而呈现各向异性.结合纤维取向分析、拉伸模量分析及泊松比分析,对注射法成型拉伸试样的方法进行初步探讨.     

短纤维增强熔体三维充模模拟及制品性能预测

基于气-液-固三相模型,给出了适用于三维流场的纤维质心虚拟速度、纤维平动与取向、动量交换源项的求解公式,建立了描述短纤维增强聚合物熔体充模过程的三维模型。采用同位网格有限体积法和Level Set界面追踪技术,实现了充模过程的三维动态模拟。并且,根据模拟计算出的平均取向角,提出了三维取向短纤维增强复合材料力学性能参数计算的一种简化模型。数值结果表明:三维模拟技术可有效反映注塑成型充模的流动过程和喷泉效应;纤维取向分析可量化显示纤维在型腔中的表层-芯层结构取向;弹性模量计算结果与实验结果吻合较好。     

基于Moldflow复合材料注射压缩成型纤维取向模拟

依据Folgar-Tucker纤维取向模型及广义非牛顿流体本构方程,采用Solidwoks软件创建了复合材料制品的三维模型,将模拟纤维在模腔中的注射压缩成型流动过程导入Moldflow软件中.对比了注射成型与注射压缩成型得到的制品中碳纤维取向程度,并预测复合材料在该取向上的导热性能.研究结果表明,制品厚度、纤维含量是影...     

浇口设计对塑件收缩规律影响的数值模拟

应用Moldflow分析工具,选用PP与ABS两种材料,以侧浇口填充方式,进行了不同浇口位置和尺寸对注塑成型收缩影响的数值模拟。模拟数据采用正交实验方法进行处理,并通过极差分析和贡献率的计算分析了各因素间的作用关系及其对成型收缩的影响规律。结果表明:不论哪种塑件结构,浇口位置变化始终是影响塑件成型收缩的主要因素;而塑件结构及浇口尺寸变化对成型收缩的影响依次减小。     

长玻纤增强聚丙烯极薄注塑试样的结构与性能研究

采用一套型腔尺寸为200 mm×50 mm×1.5 mm的薄壁样片注塑模对40%填充量的长纤维增强聚丙烯树脂(LGFPP)进行了充填试验。研究了在完全充填的条件下注塑成型制品不同位置的纤维含量、长度分布、取向情况以及对其力学性能的影响。结果表明,在成型压力和树脂所受到的剪切速率都要高于常规方法的薄壁注射成型过程中,纤维的长度损失很大;在整个试样中部稳定流动区域的纤维平均长度最长;纤维含量呈现浇口远端最高,浇口处最低的特点;纤维的取向呈现剪切层高,芯层较低的特点;纤维在基体中的含量及取向的综合效应对力学性能有显著影响。     

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。     

Mechanical properties of glass fiber reinforced polypropylene injection molded with a rotation mold

A special mold (Rotation, Compression, and Expansion Mold) was used to impose a controlled shear action during injection molding of short glass fiber reinforced polypropylene discs. This was achieved by superimposing an external rotation to the pressure‐driven advancing flow front during the mold filling stage. Central gated discs were molded with different cavity rotation velocities, inducing distinct levels of fiber orientation through the thickness. The mechanical behavior of the moldings was assessed, in tensile and flexural modes on specimens cut at different locations along the flow path. Complete discs were also tested in four‐point flexural and in impact tests. The respective results are analyzed and discussed in terms of relationships between the developed fiber orientation level and the mechanical properties. The experimental results confirm that mechanical properties of the moldings depend strongly on fiber orientation and can thus be tailored by the imposed rotation during molding. POLYM. ENG. SCI. 46:1598–1607, 2006. © 2006 Society of Plastics Engineers.     

Investigation of fiber orientation states in injection‐compression molded short‐fiber‐reinforced thermoplastics

Injection‐compression molding (ICM) has received increased attention because of its advantages over conventional injection molding (CIM). This article aims to investigate the effects of five dominating ICM processing parameters on fiber orientation in short‐fiber‐reinforced polypropylene (SFR‐PP) parts. A five‐layer structure of fiber orientation is found across the thickness under most conditions in ICM parts. This is quite different from the fiber orientation patterns in CIM parts. The fibers orient orderly along the flow direction in the shell region, whereas most fibers arrange randomly in the skin and the core regions. Additionally, the fiber orientation changes in the width direction, with most fibers arranging orderly along the flow direction at positions near the mold cavity wall. The results also show that the compression force, compression distance, and compression speed play important roles in determining the fiber states. Thicker shell regions, in which most fibers orient remarkably along the flow direction, can be obtained under larger compression force or compression speed. Moreover, the delay time has an obvious effect on the fiber orientation at positions far from the gate. However, the effect of compression time is found to be negligible. POLYM. COMPOS., 31:1899–1908, 2010. © 2010 Society of Plastics Engineers.     

Experimental study and calculations of short glass fiber orientation in a center gated molded disc

Short glass fiber orientation in a center gated molded disc of polyamide is studied using optical microscopy techniques. The very different orientation between the core and the surface of the molding is quantified with an orientation function. The influence of the molding conditions is investigated. A numerical scheme is used for modeling the mold filling with a viscous melted polymer. A computation method is introduced to describe the fiber movement during the flow. The theoretical results are in good agreement with the experimental ones. In particular, the very different orientation between the skin and the core of the disc is well predicted.     

Numerical prediction of residual stresses and birefringence in injection/compression molded center‐gated disk. Part II: Effects of processing conditions

The accompanying paper, Part I, has presented the physical modeling and basic numerical analysis results of the entire injection molding process, in particular with regard to both flow‐induced and thermally‐induced residual stress and birefringence in an injection molded center‐gated disk. The present paper, Part II, investigates the effects of various processing conditions of injection/compression molding process on the residual stress and birefringence. The birefringence is significantly affected by injection melt temperature, packing pressure and packing time. However, the thermally‐induced birefringence in the core region is insignificantly affected by most of the processing conditions. On the other hand, packing pressure, packing time and mold wall temperature affect the thermally‐induced residual stress rather significantly in the shell layer, but insignificantly in the core region. The residual stress in the shell layer is usually compressive, but could be tensile if the packing time is long, packing pressure is large, and the mold temperature is low. The lateral constraint type turns out to play an important role in determining the residual stress in the shell layer. Injection/compression molding has been found to reduce flow‐induced birefringence in comparison with the conventional injection molding process. In particular, mold closing velocity and initial opening thickness for the compression stage of injection/compression molding have significant effects on the flow‐induced birefringence, but not on the thermal residual stress and the thermally‐induced birefringence.     

Injection molding of glass fiber reinforced phenolic composites. 2: Study of the injection molding process

This study of injection molding of glass fiber reinforced phenolic molding compounds examines fiber breakage and fiber orientation with key material and processing variables, such as injection speed, fiber volume fraction, and the extent of resin pre-cure. The fiber orientation, forming discrete skin-core arrangements, is related to the divergent gate to mold geometrical transition, the extent of pre-cure and injection speed functions of the melt viscosity. Transient modifications to the melt viscosity during mold filling produce variations in skin/core structure along the flow path, which are correlated to the mechanical properties of injection moldings. The melting characteristics of the phenolic resin during plasticization impose a severe environment of mechanical attrition on the glass fibers, which is sequentially monitored along the screw, and during subsequent flow through runners and gates of various sizes. Differences found between the processing characteristics of thermosets and thermoplastics raise questions concerning the applicability of thermoplastic injection molding concepts for thermosets.     

Formation mechanism of high-pressure water penetration induced fiber orientation in overflow water-assisted injection molded short glass fiber-reinforced polypropylene

Recently, there has been growing interest in water-assisted injection molding (WAIM) not only for its advantages over gas-assisted molding (GAIM) and conventional injection molding (CIM), but also for its great potential advantages in industrial applications. To understand the formation mechanism of water penetration induced fiber orientation in overflow water-assisted injection molding (OWAIM) parts of short glass fiber-reinforced polypropylene (SGF/PP), in this work, the external fields and water penetration process within the mold cavity were investigated by experiments and numerical simulations. The results showed that the difference of fiber orientation distribution in thickness direction between WAIM moldings and CIM moldings was mainly ascribed to the great external fields generated by water penetration. Besides, fiber orientation depended on the position both across the part thickness and along the flow direction. Especially in the radial direction, fiber orientation varied considerably. The results also showed that the melt temperature is the principal parameter affecting the fiber orientation along the flow direction, and a higher melt temperature significantly facilitated more fibers to be oriented along the flow direction, which is quite different from the results as previously reported in short-shot water-assisted injection molding (SSWAIM). A higher water pressure, shorter water injection delay time, and higher melt temperature significantly induced more fibers to be orderly oriented in OWAIM moldings, which may improve their mechanical performances and broaden their application scope.     

Fiber orientation in injection molding with rotating flow

The development of fiber orientation in injection molding was manipulated by a special molding tool, the RCEM mold, which imposes a rotation action by one of the cavity surfaces during the filling stage. Center‐gated disc moldings were produced from glass fiber reinforced polypropylene with different cavity rotation velocities, inducing distinct distributions and levels of fiber orientation. The morphologies of the moldings were characterized by optical and electronic microscopy. The through‐thickness profiles of fiber orientation were assessed by means of the orientation tensor, and the relationship between the processing thermo‐mechanical environment and the fiber orientation was established. At high rotation velocities, the resulting fiber orientation pattern is mainly controlled by the rotational motion, inducing a much more homogeneous through‐the‐thickness fiber orientation distribution, with a preferential alignment on the circumferential direction. POLYM. ENG. SCI., 2008. © 2007 Society of Plastics Engineers     

The effect of orientation on the mechanical properties of injection molded polystyrene

The deformation and fracture behavior of injection molded plaques have been determined, and the results interpreted in terms of the effect of molecular orientation on the crazing and shear yielding behavior. The molecular orientation was characterized by optical birefringence. A range of injection molding conditions and two mold thicknesses were Used and this resulted in a large variation in the molecular orientation, particularly through the sheet thickness. Tensile tests were made on samples cut at different angles to the injection molding direction. The moldings are considered to consist of a composite of layers of material with different orientation, and the properties of the samples cut from the molding are analyzed in terms of the properties of each layer. Results from material oriented unidirectionally by hot drawing have been used to predict the composite properties, and good agreement has been obtained.     

Effect of polymer properties on the structure of injection-molded parts

In this study, the distributions of both molecular orientation and crystallinity along the flow direction as well as across the thickness direction of injection-molded specimens of poly(ethylene terephthalate) (PET) molded at different mold temperatures were investigated. The degree of molecular orientation at the surface of the specimens was compared with that of other injected materials (polystyrene, high density polyethylene, liquid crystal polymer) showing different thermal, rheological, and crystallization characteristics. It was found that the molecular orientation at the skin layer of the molding increases with the polymer relaxation time, the rigidity of the polymer molecules, and the crystallization rate of the polymer. Moreover, in the case of PET, it was found that the crystallinity at the skin layer and in the core of the molding depends on the mold temperature. For low mold temperatures, near the gate, the maximum of crystallinity was observed at the subskin layer because of the “shear-induced crystallization” generated during the filling stage. On increasing the mold temperature, the maximum of crystallinity was found to shift to the skin layer as a result of the decrease of the thickness of this layer. For low mold temperatures, the variation of the molecular orientation in the thickness direction was found to be much the same as for the crystallinity of the polymer. This result indicates that the shear-induced crystallization process improves the degree of molecular orientation in the flow direction since it inhibits the relaxation process of the polymer molecules.