Fiber orientation structures and mechanical properties of injection molded short glass fiber reinforced ribbed plates

In this paper we describe a study of the fiber orientation structures present within a model ribbed injection molded plate. The details of the fiber orientation at each chosen location on the injection molded parts were measured using an in-house developed image analysis system, which enabled large areas to be scanned (up to 200 mm²) up to a limit of 1 million fiber images. Two materials were used for these experiments, short glass fiber filled PBT and short glass fiber filled nylon 66. First, a comparison was made between the fiber orientation at an identical position, 28 mm from the injection gate on a transverse rib, on two plates made from glass fiber filled PBT. It was found that the fiber orientation in these two separately manufactured components was virtually identical when comparing the whole scanned area, but the differences became more significant when comparing areas on the length scale of an individual fiber (∼ 200 μm). Second, the fiber orientation at the same position was compared for two plates made using the glass/PBT and glass/nylon 66 materials. The differences for the complete scanned areas were small, confirming that mold geometry plays a crucial role in determining fiber orientation structures, and that matrix properties are secondary. Third, the fiber orientation structures at various positions across one of the glass/PBT plates were examined in greater detail, in particular across a number of the transverse ribs: the chosen ribs were of various widths and heights. Differences in structure were found depending on the local rib geometry. Finally, the effect of the measured fiber orientation structures in determining the mechanical properties of the ribbed plate was investigated using simple modeling schemes. While the stiffness of the rib/web assembly was found to depend on the average fiber orientation of the two parts, the different thermal expansions of the web and the rib, caused by the different fiber orientation in the two regions, led to significant warpage of the rib/web assembly. Polym. Compos. 25:237–254, 2004. © 2004 Society of Plastics Engineers.     

A simplified method to determine the 3D orientation of an injection molded fiber‐filled polymer

In short‐fiber reinforced composites, it is widely accepted that the fiber orientation plays an important role on their overall physical and thermomechanical properties. To predict the properties of such composite materials, a full 3D fiber orientation characterization is required. A variety of destructive and nondestructive techniques have been developed, but all the methods have the same common point that they are very tedious and time consuming. Knowing that the fiber orientation induced by the flow remains mainly in the flow plane, an easier method has been performed for injection molded fiber‐filled polymers. It is based on the simple 2D SEM image analysis of a specific 45°‐oblique section plane. Then, the indetermination of fiber orientation from an ellipse mark analysis does not exist anymore. This novelty also turns out to be much more accurate. To achieve measurements over large composite samples, the method has been fully automated. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Coupling of flow simulation and structural analysis for glass-filled thermoplastics

In the automotive industry, glass-filled thermoplastics are used in air intake manifolds, radiator tanks, and many other parts. Plastic parts have many advantages over metal parts including mass, design flexibility and parts consolidation. However, widespread application of glass-filled thermoplastic materials has been limited in many cases by the inability to accurately predict performance and durability. Fiber-filled injection-molded parts contain complex fiber orientation patterns. This fiber orientation state affects material properties including elastic modulus and strength and part properties including shrinkage and warpage. Tremendous amounts of time and money can be saved if one can predict the moldability and mechanical properties of a part at the design stage. In this work, we present a method where commercially available injection molding and structural analysis software may be coupled together with appropriate material property data to improve prediction of structural performance for parts molded from short glass fiber-filled plastics. In addition, we compare the experimental and predicted performance based on simple equations and complex finite element calculations. Two major conclusions may be drawn from this work. In general, the assumption of geometric nonlinearity must be made. Also, an orthotropic material model is generally more robust and accurate than an isotropic analysis. Polym. Compos. 25:343–354, 2004. © 2004 Society of Plastics Engineers.     

Optimization of fiber prediction model coefficients in injection molding simulation based on micro computed tomography

Fiber‐reinforced thermoplastic for low weight application become increasingly important for many industrial branches. During the injection molding of short fiber‐reinforced thermoplastic parts the fibers become orientated. This orientation is determined on the one hand by the geometry of the part, and on the other hand by the injection molding parameters, and influence the mechanical behavior of the part. The determination of the fiber properties that is, the orientation distribution of the fibers, is therefore of considerable interest. Since a more accurate fiber orientation prediction of the injection molding simulation will lead to a more precise structural simulation the objective of the present work is to achieve a preferably accurate orientation distribution. To describe the orientation distribution of the fibers, the fiber orientation tensor defined by Advani and Tucker (Advani and Tucker, Journal of Rheology, 31, 751 (1987)) was used. To determine the entries of this tensor micro computed tomography scans (μCT‐scans) of an injection‐molded plate, as well as an injection‐molded specimen with different cross section and shape were performed. Injection molding simulation using Autodesk Moldflow Insight were carried out. The residual strain closure (RSC) model was the underlying model to depict the fiber orientation distribution, or rather the orientation tensors. The two model parameters, the fiber interaction coefficient Ci and the scalar factor κ , were adapted by an optimization procedure, in such a way that the orientation distributions of the simulations fit the results of the μCT‐analysis at its best. POLYM. ENG. SCI., 59:E152–E160, 2019. © 2018 Society of Plastics Engineers     

Prediction of fiber orientation in the injection molding of long fiber suspensions

The properties of long glass fiber reinforced parts are highly dependent on the fiber orientation generated during processing. In this research, the orientation of concentrated long glass fibers generated during the filling stage of a center‐gated disk (CGD) mold was simulated. The orientation of the fibers was calculated using both the Folgar‐Tucker model and a recently developed semiflexible Bead‐Rod model. Rheologically consistent model parameters were used in these simulations, as determined from a previously proposed method, using a sliding plate rheometer and newly modified stress theory. The predicted CGD orientations were compared with experimentally measured values obtained from the parts. Both models performed very well when using model parameters consistent with the independent rheological study, and the results provide encouragement for the proposed method. Comparatively, the Folgar‐Tucker model provided slightly better orientation predictions up to 20% of the fill radius, but above 20% the Bead‐Rod model predicted better values of the orientation in both the radial and circumferential directions. The Folgar‐Tucker model, however, provided better orientation values perpendicular to the flow direction. Lastly, both models only qualitatively represented the orientation above 70% of the fill radius where frontal flow effects were suspected to be non‐negligible. The uniqueness of this research rests on a method for obtaining model parameters needed to predict fiber orientation which are independent of the experiments being simulated and a method for handling long semiflexible fiber suspensions. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Molecular orientation distributions during injection molding of liquid crystalline polymers: Ex situ investigation of partially filled moldings

The development of molecular orientation in thermotropic liquid crystalline polymers (TLCPs) during injection molding has been investigated using two‐dimensional wide‐angle X‐ray scattering coordinated with numerical computations employing the Larson–Doi polydomain model. Orientation distributions were measured in “short shot” moldings to characterize structural evolution prior to completion of mold filling, in both thin and thick rectangular plaques. Distinct orientation patterns are observed near the filling front. In particular, strong extension at the melt front results in nearly transverse molecular alignment. Far away from the flow front shear competes with extension to produce complex spatial distributions of orientation. The relative influence of shear is stronger in the thin plaque, producing orientation along the filling direction. Exploiting an analogy between the Larson–Doi model and a fiber orientation model, we test the ability of process simulation tools to predict TLCP orientation distributions during molding. Substantial discrepancies between model predictions and experimental measurements are found near the flow front in partially filled short shots, attributed to the limits of the Hele–Shaw approximation used in the computations. Much of the flow front effect is however “washed out” by subsequent shear flow as mold filling progresses, leading to improved agreement between experiment and corresponding numerical predictions. POLYM. ENG. SCI.,, 2011. © 2011 Society of Plastics Engineers     

Modeling of fiber–polymer coupling for suspensions of mono‐modal fibers

The rheology of suspensions of fibers in polymer solutions is strongly dependent on fiber–fiber and fiber–polymer interactions. To model these interactions and their dependence on the flow and suspension properties, the steady shear viscosity of glass fibers in a polyethylene oxide polymer solution are measured for different fiber volume fractions and aspect‐ratios. The measurements are conducted for well characterized fiber samples that have a uniform and well defined aspect‐ratio and for moderate volume fractions. The results of the experimental study are used to correlate the polymer–fiber coupling factor and the fiber–fiber interaction coefficient using a mathematical model based on a modified FENE‐P (finitely extensible nonlinear elastic) constitutive equation. It was found that both parameters are strongly dependent on the characteristics of the suspension, but also depend on the flow shear rate that determines the degree of fiber orientation. In general, fiber–fiber and polymer–fiber interactions increase with both the aspect‐ratio and the volume fraction and are more important when the fibers are not fully oriented. POLYM. COMPOS., 27:82–91, 2006. © 2005 Society of Plastics Engineers     

长玻璃纤维增强热塑性塑料纤维取向模型

通过对纤维取向模型演化发展的综述,阐述了长玻璃纤维增强热塑性塑料（LFRTs）纤维取向模型的基本理论思想和基于工程应用的表达式。纤维取向模型的演化始于Folgar-Tucker基本模型,继而向各向异性和演化阻滞两个方向改进,并最终形成了预测LFRTs纤维取向的ARD-RSC模型和iARD-RPR模型。基于长玻璃纤维增强聚丙烯注塑样条中玻璃纤维取向的CT扫描实测结果,研究了两个模型的预测准确性。     

Experimental investigation and numerical simulation of granite powder filled polymer composites for wind turbine blade: A comparative analysis

This paper describes the mechanical, thermo‐mechanical, and thermal behavior of unfilled E‐glass fiber (10–50 wt%) reinforced polymer (GFRP) composites and granite powder filled (8–24 wt%) GFRP composite in different weight percentages, respectively. The void fraction of unfilled glass epoxy composite is decreased from 7.71% to 3.17% with the increase in fiber loading from 10 to 50 wt%. However, void fraction for granite powder filled GFRP composites show reverse in trend. The granite powder addition in glass‐epoxy composites show significant improvement in hardness (37–47 Hv), impact strength (31.56–37.2 kJ/m²), and stress intensity factor (by 14.29% for crack length of 5 mm) of the composites. The thermo‐mechanical analyses also show strong correlation with the mechanical performance of the composites. The minimum difference of 0.17 GPa in storage and flexural moduli are observed for unfilled 20 wt% glass epoxy composite; whereas, maximum difference of 0.71 GPa is recorded for unfilled 50 wt% glass epoxy composite. Moreover, the numerical and experimentally measured thermal conductivity of unfilled and granite powder filled epoxy composites are within the lower and upper bound values. Hence, a successful attempt is presented for mechanical analysis of full scale model by finite element analysis. The results show that finite element analysis predicted reasonably actual stress value and tip deflection of wind turbine blade. POLYM. COMPOS., 38:1335–1352, 2017. © 2015 Society of Plastics Engineers     

Effects of fiber aggregates on the transverse mechanical behavior of commingled PP–glass fiber composites

In previous articles, mechanical models were proposed to predict the reinforcement effect of polymers by particulates as well as unidirectional fibers over wide ranges of volume fraction of fillers and temperatures. On the basis of image analyses and the definition of representative morphological motifs, these models are able to predict the viscoelastic properties of quasi‐isotropic and unidirectional composites or to extract the behavior of a phase, such as the interphase in filled rubbers or the transcrystalline phase in semicrystalline polymers. In this work, based on a 2D image processing, this approach is extended to predict the viscoelastic properties of commingled PP–glass fiber composites. It is shown that fiber aggregates, composed of fibers and surrounding polymer, might be considered as the reinforcing phase. In addition, the different failure modes of these composites are separated as a function of the volume fraction of fillers or temperature. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3466–3476, 2006     

Fiber orientation in divergent/convergent flows in expansion and compression injection molding

This study compares the fiber orientation patterns of short glass fiber‐reinforced polypropylene developed in conventional and nonconventional injection molding, the latter using a special mold, RCEM (rotation, compression, and expansion mold). This mold allows for a wide variety of operating modes during mold filling, which leads to a great versatility in obtaining different fiber orientation patterns. By incorporating through‐thickness convergent and divergent flows during the filling stage (compression and expansion modes, respectively), the fiber orientation can be tailored. These linear dynamics can be superimposed with a simultaneous rotational movement of one of the mold surfaces. These combined actions induce a high fiber orientation transversely to the radial flow direction, this effect being more pronounced in the expansion mode. POLYM. COMPOS. 27:539–551, 2006. © 2006 Society of Plastics Engineers     

Properties enhancement of short glass fiber‐reinforced thermoplastics via sandwich injection molding

This article demonstrates using sandwich injection molding in order to improve the mechanical properties of short glass fiber‐reinforced thermoplastic parts by investigating the effect of fiber orientation, phase separation, and fiber attrition compared to conventional injection molding. In the present case, the effect of short glass fiber content (varying from 0–40 wt%) within the skin and core materials were studied. The results show that the mechanical properties strongly depend not only on the fiber concentration, but also on the fiber orientation and the fiber length distribution inside the injection‐molded part. Slight discrepancies in the findings can be assumed to be due to fiber breakage occurring during the mode of processing. POLYM. COMPOS., 26:823–831, 2005. © 2005 Society of Plastics Engineers     

HDPE reinforced with glass fibers: Rheology,tensile properties,stress relaxation,and orientation of fibers

Glass fiber‐reinforced high‐density polyethylene of varying concentrations was mixed with ethylene copolymer and maleic anhydride‐grafted polypropylene (coupling agents) separately. The viscosity, tensile strength, and stress relaxation properties of the composites were investigated. The orientation and anisotropy of glass fibers were studied using micro computed tomography scanner. It was found out that the orientation and anisotropy of fiber are strongly affected by the increase in glass fiber concentration. POLYM. COMPOS., 35:2159–2169, 2014. © 2014 Society of Plastics Engineers     

Two‐dimensional long‐flexible fiber simulation in simple shear flow

Long‐flexible fiber orientation under the influence of a flow field is an important engineering problem. One can encounter this problem in many fields. For example in fiber reinforced thermoplastics produced in both injection and compression molding, fiber orientation affect final part properties. Fiber orientation models are constructed for short fibers in a simple shear flow case and though this case is important it is not the general case. In this work we extract rotational friction coefficients from Jeffery's model, create a general case long‐flexible fiber orientation model, and apply it in a simple shear flow. POLYM. COMPOS., 37:2425–2433, 2016. © 2015 Society of Plastics Engineers     

Applications of a fiber orientation prediction algorithm for compression molded parts with multiple charges

An application of a finite element simulation of mold filling and predication of fiber orientation in fiber filled compression molded parts is presented. Three-dimensional thin-walled geometries are considered. Following a simulation of the filling process, a set of transort equations are solved to predict the locally planar orientation of short fiber composites. The final orientation states throughout the part provide the necessary information to obtain a locally orthotropic mechanical model of the composite. A sheet molding compound part with a multiple charge pattern is used to illustrate the generality of the algorithms developed for compression flow, fiber orientation, and property predications. Derivations of the orthotropic mechanical properties obtained from the fiber orientation results are outlined.     

Prediction of fiber orientation in a rotating compressing and expanding mold

In the rotating/compressing/expanding mold (RCEM), one mold wall can expand, compress, and rotate during injection molding, thus offering opportunities to control the thermomechanical history of a polymer and its microstructure. A computer simulation of flow and fiber orientation in RCEM was developed. The predictive model extends the generalized Hele‐Shaw formulation to account for compression/expansion and rotation of the mold wall, and uses the Folgar–Tucker model for fiber orientation predictions. A 20% GF polypropylene was molded under various molding conditions. The predicted fiber orientation distributions were compared with experiments. The model compares favorably with experiments, provided that the fiber orientation equation is modified by a strain‐reduction factor that slows the transient development of fiber alignment. The effect of fountain flow on orientation must also be included to correctly predict fiber orientation near the mold walls, mainly for the case of stationary and linear motions of the mold surface. Compression or expansion of the mold has only a small effect on fiber orientation, but rotation of the mold dramatically changes the orientation, causing fibers to align in the tangential direction across the entire thickness of the molding. This rotation action perturbs the fountain flow and becomes the dominant factor affecting fiber alignment across the entire cavity thickness. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers.     

Mechanical properties of injection molded long fiber polypropylene composites,Part 1: Tensile and flexural properties

Innovative polymers and composites are broadening the range of applications and commercial production of thermoplastics. Long fiber‐reinforced thermoplastics have received much attention due to their processability by conventional technologies. This study describes the development of long fiber reinforced polypropylene (LFPP) composites and the effect of fiber length and compatibilizer content on their mechanical properties. LFPP pellets of different sizes were prepared by extrusion process using a specially designed radial impregnation die and these pellets were injection molded to develop LFPP composites. Maleic‐anhydride grafted polypropylene (MA‐g‐PP) was chosen as a compatibilizer and its content was optimized by determining the interfacial properties through fiber pullout test. Critical fiber length was calculated using interfacial shear strength. Fiber length distributions were analyzed using profile projector and image analyzer software system. Fiber aspect ratio of more than 100 was achieved after injection molding. The results of the tensile and flexural properties of injection molded long glass fiber reinforced polypropylene with a glass fiber volume fraction of 0.18 are presented. It was found that the differences in pellet sizes improve the mechanical properties by 3–8%. Efforts are made to theoretically predict the tensile strength and modulus using the Kelly‐Tyson and Halpin‐Tsai model, respectively. POLYM. COMPOS., 28:259–266, 2007. © 2007 Society of Plastic Engineers     

Influence of fiber orientation and fiber content on properties of sisal‐jute‐glass fiber‐reinforced polyester composites

The incorporation of natural fibers with polymer matrix composites (PMCs) has increasing applications in many fields of engineering due to the growing concerns regarding the environmental impact and energy crisis. The objective of this work is to examine the effect of fiber orientation and fiber content on properties of sisal‐jute‐glass fiber‐reinforced polyester composites. In this experimental study, sisal‐jute‐glass fiber‐reinforced polyester composites are prepared with fiber orientations of 0° and 90° and fiber volume of sisal‐jute‐glass fibers are in the ratio of 40:0:60, 0:40:60, and 20:20:60 respectively, and the experiments were conducted. The results indicated that the hybrid composites had shown better performance and the fiber orientation and fiber content play major role in strength and water absorption properties. The morphological properties, internal structure, cracks, and fiber pull out of the fractured specimen during testing are also investigated by using scanning electron microscopy (SEM) analysis. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42968.     

Evaluation of processing effects in injection‐molded amorphous and crystalline thermoplastics using an excimer laser

The ablation behavior of amorphous [polystyrene (PS), polycarbonate (PC)] and crystalline [PET, glass‐filled poly(butylene terephthalate) (PBT)] polymers by 248‐nm KrF excimer laser irradiation were investigated for different injection‐molding conditions, namely, injection flow rate, injection pressure, and mold temperature, as a possible method for evaluating processing effects in the specimens. For this purpose, dumbbell‐shaped samples were injection‐molded under different sets of processing conditions, and weight loss measurements were carried out for the different injection‐molding conditions. Some of the crystalline (PET) samples were annealed at different annealing times and temperatures. For PET, the weight loss decreased with increasing mold temperature and remained insensitive to injection flow rate. Annealing time and temperature significantly reduced weight loss in PET. For PBT, the weight loss due to laser ablation decreased with increasing material packing due to pressure, and it also showed some sensitivity to flow rate variation. The major effect was seen with glass‐filled PBT samples. The weight loss decreased drastically with increasing glass fiber content. Laser ablation allowed us to observe process‐induced fiber orientation by scanning electron microscopy in PBT samples. For PS and PC, the weight loss increased with increasing injection flow rate and mold temperature and decreased with increasing injection pressure. The position near the gate showed higher ablation than the position at the end for all the conditions. A decrease in the material orientation with injection speed and mold temperature led to an increase in the weight loss, whereas an increase in the injection pressure, and consequently orientation, led to a lower weight loss for PS and PC. Higher residual stress samples showed higher weight losses. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 2006     

Comparison of the guarded‐heat‐flow and transient‐plane‐source methods for carbon‐filled nylon 6,6 composites: Experiments and modeling

In this study, two different carbons (synthetic graphite particles and carbon fiber) were added to nylon 6,6, and the resulting composites were tested for thermal conductivity. The first goal of this work was to compare through‐plane thermal conductivity results from the guarded‐heat‐flow method and the transient‐plane‐source method. The results showed that both test methods gave similar through‐plane thermal conductivity results for composites containing 10–40 wt % synthetic graphite and for composites containing 5–40 wt % carbon fiber. The advantages of using the transient‐plane‐source method were that the in‐plane thermal conductivity was also measured and the experimental time was shorter than that of the guarded‐heat‐flow method. The second goal of this work was to develop and use a detailed finite‐element analysis to model heat transfer within a carbon‐filled nylon 6,6 composite sample for the transient‐plane‐source method and compare these results to actual experimental results. The results showed that the finite‐element model compared well with the actual experimental data. The finite‐element model could be used in the future as a design tool to predict the dynamic thermal response of different composite materials for many applications. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006