Comparative study of weld-line strength for unfilled and glass-filled thermoplastic polyamide-6 materials

The injection molding process is widely accepted for the processing of engineering thermoplastics due to the ease of manufacturing complex designs. Weld-line is a defect occurring in injection molded parts when two flow fronts join each other. At weld-line locations, parts exhibit lower mechanical strength mainly due to inadequate intermolecular diffusion and fiber orientation anisotropy. The present work is aimed at investigating and comparing weld-line strength for unfilled and glass-filled polyamide-6 materials. To achieve this, polyamide-6 unfilled, 30% glass-filled, and 50% glass-filled materials are used to manufacture plaques. The special-purpose mold is designed to obtain plaques with and without weld-lines with help of Moldflow simulations. The specimens for tensile tests are then cut from molded plaques and experimental testing is conducted to evaluate tensile properties. Fractured surfaces of specimens are examined using a scanning electron microscope. The results demonstrated a significant drop in tensile strength and modulus for glass-filled material weld-line specimens when compared to specimens of no weld-line. However, for unfilled specimens, tensile strength and modulus are almost the same for samples with and without weld-line. A reduction in tensile strength of 13%, 49%, and 57% is observed for unfilled, 30% glass-filled, and 50% glass-filled polyamide-6 material respectively.     

Prediction of fiber orientation distribution in injection molded parts using Moldex3D simulation

In the automotive industry, glass‐filled thermoplastics are used in air intake manifolds, radiator tanks, and many other parts. However, widespread application of glass‐filled thermoplastic materials has been limited in many cases by the inability to accurately predict performance and durability. Since a more accurate fiber orientation prediction will lead to more accurate local mechanical property predictions, this work investigated a recently proposed mathematic model of fiber suspension rheology, which considers the anisotropic fiber diffusion and fiber–matrix interaction from a microscopic viewpoint. The new model proved able to predict many details of the fiber orientation distribution and could be applied advantageously as part of the product and manufacturing development processes. POLYM. COMPOS., 35:671–680, 2014. © 2013 Society of Plastics Engineers     

Prediction of fiber orientation in injection molded parts of short-fiber-reinforced thermoplastics

Fiber orientation induced by injection mold filling of short-fiber-reinforced thermoplastics (FRTP) causes anisotropy in material properties and warps molded parts. Predicting fiber orientation is important for part and mold design to produce sound molded parts. A numerical scheme is presented to predict fiber orientation in three-dimensional thin-walled molded parts of FRTP. Folgar and Tucker's orientation equation is used to represent planar orientation behavior of rigid cylindrical fibers in concentrated suspensions. The equation is solved about a distribution function of fiber orientation by using a finite difference method with input of velocity data from a mold filling analysis. The mold filling is assumed to be nonisothermal Hele-Shaw flow of a non-Newtonian fluid and analyzed by using a finite element method. To define a degree of fiber orientation, an orientation parameter is calculated from the distribution function against a typical orientation angle. Computed orientation parameters were compared with measured thermal expansion coefficients for molded square plates of glass-fiber-reinforced polypropylene. A good correlation was found.     

Effect of screw design on fiber damage in extrusion compounding and composite properties

The mechanism of fiber length degradation during twin screw extrusion compounding and methods to reduce it through process and machine design are extremely important in discontinuous fiber reinforced composites. Fiber damage along the screw and the extruder die are determined for three screw designs with different mixing sections. The pellet quality, wet-out, and fiber dispersion in the extruded strands are compared. The fiber orientation distributions in the screw are determined to identify regions of higher fiber interaction. The fiber damage during subsequent injection molding has also been determined. The tensile, flexural, and impact properties of the tensile bars are compared. It is found that the residence time, fill-up, and the intesity of mixing during extrusion compounding have a predominant effect on fiber length degradation. The screw designs were seen to have a greater effect on the fiber damage in the 40 wt% glass-filled polymer than the 30 wt% glass-filled polymer. However, the mechanical properties of the 30 wt% glass-filled polymer showed an increasing trend compared to the 40 wt% glass filled polymer. A screw design that provides a balance of the fiber length, wet-out, and fiber dispersion was noted to give consistent mechanical properties.     

Numerical investigation of three-dimensional fiber suspension flow by using finite volume method

Fiber suspension flow is common in many industrial processes like papermaking and fiber-reinforcing polymer-based material forming. The investigation of the mechanism of fiber suspension flow is of significant importance, since the orientation distribution of fibers directly influences the mechanical and physical properties of the final products. A numerical methodology based on the finite volume method is presented in the study to simulate three-dimensional fiber suspension flow within complex flow field. The evolution of fiber orientation is described using different formulations including FT model and RSC model. The pressure implicit with splitting of operators algorithm is adopted to avoid oscillations in the calculation. A laminate structure of fiber orientation including the shell layer, the transition layer and the core layer along radial direction within a center-gated disk flow channel is predicted through a three-dimensional simulation, which agrees well with Mazahir’s experimental results. The evolution of fiber orientation during the filling process within the complex flow field is further discussed. The mathematical model and numerical method proposed in the study can be successfully adopted to predict fiber suspension flow patterns and hence to reveal the fiber orientation mechanism.     

Practical use of the statistically modified laminate model for injection moldings. Part 1: Method and verification

The fibers in injection molded FRP provide the material's strength and stiffness; however, they also supply many of the problems. Preferential orientation of fibers during molding can reduce strength and stiffness below expected values in critical directions, or induce warpage in thin walled sections. Makers of short fiber reinforced injection molded products typically use computer aided engineering packages to optimize product performance and manufacturing variables. However, the reliability of the fiber orientation simulation can be limited, and the method is not easily understood, making an assessment of accuracy for a given situation difficult. In addition, the structural module of flow analysis packages is often a basic package with many features missing. This paper presents a structural analysis system for injection molded parts made of short fiber reinforced plastics. A full-featured commercial structural analysis code is interfaced with a flow analysis program using a practical material model that takes into account the effects of local fiber orientation. The system is completely open to the user, and can be modified as required.     

The role of the interaction coefficient in the prediction of the fiber orientation in planar injection moldings

The mechanical properties of injection molded parts in glass reinforced materials are sensitive to processing. A successful design requires a good estimate of the product performance before production. Its performance is strongly affected by the fiber orientation field set up during processing. The fiber orientation pattern is complex and varies three‐dimensionally in the moldings. Some commercial simulation programs already allow the prediction of the fiber orientation induced during the flow by the associated stress field. The results from the simulations are dependent on a parameter accounting for the interactions between fibers during the flow, known as the fiber interaction coefficient. In this paper the effectiveness of the interaction parameter on controlling the predicted patterns of the fiber orientation is studied. This is done by comparing and analyzing the experimental data and the corresponding predictions.     

Process induces fiber orientation: Numerical simulation with experimental verification

The performance of short fiber molded composite structures is determined uniquely by the properties of the molding material and the process induced fiber orientation. Consequently, the capability to accurately predict the fiber orientation distribution is of fundamental importance in computer-aided mold design. Methodology for the numerical prediction of fiber orientation during the mold-fill process is presented for a short glass fiber thermoset (57 percent phenolic resin, 10 percent calcium carbonate filler, and 33 percent glass fiber by volume). On the basis of a finite element flow characterization, Jeffery's orientation equation is numerically integrated along streamlines to calculate fiber orientation. Correlation of experimental and numerical results for an end-gated bar with a molded-in hole is reasonably good.     

Numerical simulation of three‐dimensional fiber orientation in injection molding including fountain flow effect

It is essential to predict the nature of flow field inside mold and flow‐induced variation of fiber orientation for effective design of short fiber reinforced plastic parts. In this investigation, numerical simulations of flow field and three‐dimensional fiber orientation were carried out in special consideration of fountain flow effect. Fiber orientation distribution was described using the second‐order orientation tensor. Fiber interaction was modeled using the interaction coefficient C_I. Three closure approximations, hybrid, modified hybrid, and closure equation for C_I=0, were selected for determination of the fiber orientation. The fiber orientation routine was incorporated into a previously developed program of injection mold filling (CAMPmold), which was based on the fixed‐grid finite element/finite difference method assuming the Hele‐Shaw flow. For consideration of the fountain flow effect, simplified deformation behavior of fountain flow was employed to obtain the initial condition for fiber orientation in the flow front region. Comparisons with experimental results available in the literature were made for film‐gated strip and centergated disk cavities. It was found that the orientation components near the wall were were accurately predicted by considering the fountain flow effect. Test simulations were also carried out for the filling analysis of a practical part, and it was shown that the currently developed numerical algorithm can be effectively used for the prediction of fiber orientation distribution in complex parts.     

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.     

Simulation of foaming in reaction injection molding

Blowing agents are often used in the reaction injection molding process to compensate for the shrinkage that occurs upon polymerization, thereby creating a structural foam part. Controlling the thickness of the solid skin and foamed core is essential to achieve the intended mechanical properties of the molded part. A numerical model was developed to predict the foaming behavior in reaction injection molding. This algorithm employs a novel primitive cell construction to enable it to analyze complex rectangular geometries, including inserts, with a two-dimensional, finite difference solution method. The analysis was applied to foaming of polyurethane in a rectangular cavity. The predicted skin thickness was found to be in good agreement with actual structural foam parts. Foaming as a function of cavity thickness was also treated. The algorithm Is useful for understanding and interpreting nonlinear phenomena of rapid, exothermic polymerizations such as foam formation adjacent to the mold wall or around a metal insert. The results can be used to formulate design guidelines for achieving desired skin/core thicknesses as a function of design, material, and process parameters.     

A model to predict the strength of short fiber composites

The material properties of short fiber composites, such as modulus, strength and thermal expansion, are greatly dependent on the fiber orientation state in the composite. Although the orientation pattern is often quite complex, models that allow its prediction have been successfully applied in combination with micromechanical models to calculate moduli and thermal properties. This paper describes the derivation of a model to predict the strength of short fiber composites with arbitrary fiber orientation and fiber length distribution based on classical (micro-) mechanical theories. The predictions are in good agreement with data measured on short fiber composites with different fiber contents.     

Integrated simulation to predict warpage of injection molded parts

Injection molding analysis programs were developed for CAE (Computer Aided Engineering) in injection molding of thermoplastics. The programs consist of mold cooling, polymer filling-packing-cooling, fiber orientation, material properties and stress analyses. These programs are integrated to predict warpage of molded parts by using a common geometric model of three dimensional thinwalled molded parts. The warpage is predicted from temperature difference between upper and lower surfaces, temperature distribution, flow induced shear stress, shrinkage, and anisotropic mechanical properties caused by fiber orientation in the integrated simulation. The integrated simulation was applied to predicting warpage of a 4-ribbed square plate of glass fiber reinforced polypropylene for examination of its validity. Predicted saddle-like warpage was in good agreement with experimental one.     

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     

PEG-PLA-PCL based electrospun yarns with curcumin control release property as suture

This work presents an interesting method using an electrospinning process to fabricate suture yarns loaded with curcumin to achieve reasonable mechanical properties as well as tunable drug release behavior. Different structures including different yarn counts and twists as well as core-sheath structures were used to adjust drug release properties along with improving the yarn's mechanical properties. The core parts were made of polycaprolactone and the sheath parts were made of polyethylene glycol, polylactic acid, and polycaprolactone. Drugs can be incorporated in both parts based on the required condition and application. Electrospun yarns were compared using both structural properties and their drug release profiles as metrics. The results of comparing drug release profiles of six electrospun yarns with different yarn counts and twists showed that yarns with finer fiber diameters in the core part have more drug release as well as more initial release. Overall evaluations showed that core-sheath drugloaded yarn with appropriate physical and mechanical properties can be a useful material as a drug delivery system to the site of damaged tissue. It can also be concluded that the amount and duration of drug release can be controlled using the structural parameters of electrospun yarns as an engineering tool for designing suture yarns with required properties.     

Digital light processing of wollastonite-diopside glass-ceramic complex structures

In this work, the possibility of shaping a glass-filled photosensitive polymer resin with Digital Light Processing (DLP) into a complex 3D structure and transforming it subsequently into a bioactive glass-ceramic scaffold was investigated. The influence of the printing conditions and the heat-treatment was studied using a 41?vol% glass-filled acrylated polymer resin. Scaffolds with designed architecture were turned into a wollastonite-diopside glass-ceramic at 1100?°C. They completely maintained their shape, exhibited no viscous flow and showed a homogenous linear shrinkage of around 25%. At 83?vol% porosity structures with Kelvin cell design exhibited a compressive strength exceeding 3?MPa, demonstrating that the material is suitable for the fabrication of bioceramic scaffolds for bone tissue engineering applications.     

Influence of the cooling conditions on the temperature and crystallinity profiles generated in a sisal fiber reinforced-polycaprolactone/starch molded part

In this work, we performed the simulation of the temperature and relative degree of crystallinity developed across the thickness of a sisal fiber reinforced-polycaprolactone/starch (30%SF-PCL/S) molded part under different cooling conditions. The non-isothermal kinetic model of Kamal and Chu (13) was used to predict the degree of crystallinity profiles. In order to obtain the temperature profiles, the energy equation was solved by treating the composite as a continuum using mass averaged physical properties. The results indicated that for cooling at a constant wall temperature, gradient-less crystallinity profiles for a wall temperature of 283 K and thicknesses lower than 10 mm are obtained. On the other hand, when cooling at a constant cooling rate, paired degree of crystallinity pieces can be obtained only for thicknesses lower than 2 mm. The continuum numerical approach used herein has the ability of predicting the optimal cooling cycle for manufacturing thick and crystallinity gradient-less SF-PCL/S parts. Polym. Compos. 25:461–469, 2004. © 2004 Society of Plastics Engineers.     

多尺度联合仿真在汽车注塑零件减量化设计中的应用研究

为提高复合材料注塑件的仿真准确性,基于多尺度联合仿真方法,以汽车发动机正时链条导轨为例,根据导轨纤维配向以及结构应力分布情况,设计了导轨减量化结构,在保证整体应力水平在安全范围内的同时,最大应力降低了12％,质量减轻了4％,实现了汽车发动机正时链条导轨的减量化设计.     

Time–temperature superposition principle applied to a kenaf‐fiber/high‐density polyethylene composite

The time–temperature superposition principle was applied to the viscoelastic properties of a kenaf‐fiber/high‐density polyethylene (HDPE) composite, and its validity was tested. With a composite of 50% kenaf fibers, 48% HDPE, and 2% compatibilizer, frequency scans from a dynamic mechanical analyzer were performed in the range of 0.1–10 Hz at five different temperatures. Twelve‐minute creep tests were also performed at the same temperatures. Creep data were modeled with a simple two‐parameter power‐law model. Frequency isotherms were shifted horizontally and vertically along the frequency axis, and master curves were constructed. The resulting master curves were compared with an extrapolated creep model and a 24‐h creep test. The results indicated that the composite material was thermorheologically complex, and a single horizontal shift was not adequate to predict the long‐term performance of the material. This information will be useful for the eventual development of an engineering methodology for creep necessary for the design of structural building products from these composites. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1995–2004, 2005