bluuebunny/crossref_metadata_2025_split huggingface dataset:
Flow‐induced fiber orientation in injection molded fit fiber reinforced polypropylene
Authors: Aurich T. , Mennig G. 
Published: April 2004

AbstractA through experimental study of flax fiber orientation in a plate processed by injection molding is presented. The state of orientation is described by oriental tensors and partly by frequency distribution diagrams. Composite stiffness is predieted by use of a modified classical laminate theory including unidirectional mels and orientation averaging. Comparison of the measured and calculated modulus in tension shows good agreement.
Powder coating of sheet molding compound (SMC) body panels
Authors: Abrams Lisa M. , Castro Jose M. 
Published: April 2004

AbstractSheet Molding Compound (SMC) compression molded parts are prone to porosity. During top coat baking, trapped air in the surface porosity expands and often blows through the paint leaving unacceptable craters in the final finish. The accepted solution to this problem in the SMC industry is to use a coating compound on the SMC part. The coating compound (called in‐mold coating (IMC)) is injected and cured on the SMC molding after its cure is complete, but before removing it from the mold. Another potential solution is to powder coat the parts once they have been de‐molded. While powder coating adds time to the process, it is performed outside of the mold and frees the mold for the next molding cycle earlier than if the IMC process is used. In the present paper, we develop a simplified model for the powder coating of plastic parts. We show how the model can be combined with chemo‐rheological measurements to guide the optimization of the process and material parameters. Although with the powders currently available, the surface appearance is inferior to the one obtained with IMC, this process shows potential.
EVOH/clay nanocomposites produced by melt processing
Authors: Aktzi N. , Nir Y. , Wang D. , Narkis M. , Siegmann A. 
Published: April 2004

AbstractEthylene‐vinyl alcohol copolymer(EVOH)/clay nanocomposites were prepared via a dynamic melt‐intercalation process. The phase morphology and the crystallization behavior of the nanocomposites were investigated, using DSC, DMTA, XRD and SEM. It was found that the treated clay content and dynamic processing time affect the viscosity of the EVOH/clay mixtures: higher clay contents and longer mixing times result in higher torque/viscosity levels. This is due to the increased interaction of the molten polar matrix (EVOH) with the treated organosilicate surface. Under the dynamic high shearing forces, the polymer penetrates the clay agglomerates/aggregates, intercalates within the organoclay galleries, and finally causes delaniination. Thermal analysis of the EVOH/clay nanocomposites showed that the melting temperature, crystallization temperature and heat of fusion of the EVOH matrix, sharply decrease with increasing both, the clay content and processing time. The intercalation level was characterized by X‐ray diffraction (XRD), which verified an increased gallery height. The DMTA spectra showed that longer processing times resulted in higher damping (E″ intensity) levels of the EVOH/clay composites, indicating higher fractions of the EVOH amorphous phase. However, no Tg changes were seen in spite of the high polymer/treated clay interaction levels, which may be attributed to a plasticizing effect of the low molecular weight organic cations.
Optimization of cure kinetics parameter estimation for structural reaction injection molding/resin transfer molding
Authors: Duh Robert J. , Mantell Susan , Vogel Jeffrey H. , Maier Robert S. 
Published: April 2004

AbstractA numerical method is proposed for polymer kinetic parameter estimation of either Structural Reaction Injection Molding (SRIM) or Resin Transfer Molding (RTM). The method simulates either radial flow or axial flow of reactive resins through a fiber preform inside a mold cavity. This method considers a non‐isothermal environment with different inlet boundary conditions. Based on the molding conditions, this method can find the best values of chemical kinetic parameters by comparing the simulated temperature history and the experimental temperature history. Since the kinetic parameters are estimated with the real molding conditions, the simulations using these parameter values can have better agreement with molding data than those parameters which are obtained from idealized conditions such as Differential Scanning Calorimeter (DSC). The optimization approach was verified by estimating kinetics parameters for RTM data available in the literature. Temperatures predicted by the optimized kinetics parameters are compared with experimental data for two different molding conditions: injection of a thermally activated resin into a radial mold under constant pressure flow, and injection of a mix activated resin into a radial mold under constant volume. In both cases, the optimized kinetics parameters fit the temperature data well.
Tensile properties and damage behaviors of glass‐bead‐filled modified polyphenylene oxide under large strain
Authors: Tsui C. P. , Tang C. Y. , Lee T. C. 
Published: April 2004

AbstractBased on Continuum Damage Mechanics (CDM), a damage model for glass‐bead‐filled modified polyphenylene oxide (GB/PPO) has been proposed to describe its damage behavior at various levels of tensile strain by considering the reduction of effective loading area. Hence, an equation for prediction of effective elastic modulus of the damaged GB/PPO composites in terms of the three principal true strains was derived. The tensile properties and damage behaviors of the GB/PPO composites with different volume percentages of glass beads were investigated using standard tensile tests and load‐unload tests, respectively. The addition of glass beads increases Young's modulus of PPO but has a weakening effect on its tensile strength. A maximum value of tensile work to break and tensile strain at break was found when 5 vol% of glass beads with a mean diameter of 11 μm was blended with PPO. These results were justified through microscopic examination of the fracture surfaces of the tensile specimens by using a scanning electron microscope (SEM). In‐situ observations of the strain damage processes were made through the SEM equipped with a tensile stage to determine the strain at fully debonding of glass beads. The volumetric strain of GB/PPO composites increases because of microcavitation during strain damage. In general, the prediction for the effective elastic modulus of the damaged GB/PPO composites at different true strains is slightly higher than the experimental results. The damage evolution rates after fully debonding of glass beads from the matrix are close to those predicted by the proposed damage model.
Fatigue behavior of textile composite materials subjected to tension‐tension loads
Authors: Gowayed Yasser , Fan Hong 
Published: April 2004

AbstractA model was constructed to evaluate the fatigue behavior of textile composite materials under tension‐tension loads. First, traditional FEA was used to evaluate the stiffness reduction and energy release rate due to crack propagation. Results obtained from this study were coupled with data on strength degradation of impregnated yarns under fatigue loading. Second, stiffness and strength degradation were integrated within a hybrid finite element analysis model, which uses a geometric description of textile composites. An iterative loading procedure was used to apply load and distribute stresses on a unit cell of the textile composites for each fatigue load cycle. Crack initiation and propagation were monitored during each hybrid FE load cycle ana strength and stiffness were accordingly degraded. Finally, results obtained from the analytical model were compared to experimental data for 3D angle interlock carbon/epoxy woven composites and showed a good agreement.
Durability study of a polymeric composite material for structural applications
Authors: Al‐Haik M. S. , Garmestani H. 
Published: April 2004

AbstractAn experimental study was carried out to investigate the mechanical behavior of a structural carbon based composite for infrastructure industry. Creep and load relaxation experiments were conducted to investigate the rate sensitivity behavior for a temperature range of 20–60°C. The results show that the mechanical properties were degraded under elevated temperature conditions. A threshold stress was measured, at any given temperature, below which no observable strain rate is detected. Results show that load relaxation experiment can be used as an effective tool to study durability and long‐time creep behavior. The load relaxation test methodology for the prediction of model parameters was found to be more time and cost efficient than traditional long‐time creep tests.
The prediction of permeability for an epoxy/E‐glass composite using optical coherence tomographic images
Authors: Dunkers Joy P. , Phelan Frederick R. , Zimba Carl G. , Flynn Kathleen M. , Sanders Daniel P. , Peterson Richard C. , Parnas Richard S. , Li Xingde , Fujimoto James G. 
Published: April 2004

AbstractKnowledge of the permeability tensor in liquid composite molding is important for process optimization. Unfortunately, experimental determination of permeability is difficult and time consuming. Numerical calculation of permeability from a model reinforcement can circumvent experimentation. However, permeability predictions often rely on a model reinforcement that does not accurately mimic the actual microstructure. A rapid, nondestructive technique called optical coherence tomography (OCT) can image the microstructure of a composite in minutes. Actual microstructural information can be then used to improve the accuracy of the model and therefore the predicted permeability. Additionally, the influence on fiber volume fraction and microstructural variability on permeability can be systematically studied.In this work, binary images were generated from the low contrast OCT data through image de‐noising, contrast enhancement and feature recognition. The resulting data were input to a lattice‐Boltzmann model for permeability prediction. The influence of the fiber volume fraction, tow surface area, average mean free channel path, and variable microstructure are discussed in terms of their individual and synergistic effects on permeability. The calculated axial and transverse permeabilities from the images show very good agreement with the experimental values.
Hydrodynamically induced preform deformation
Authors: Parnas Richard S. , Schultheisz Carl R. , Ranganathan Sridhar 
Published: April 2004

AbstractLarge pressure gradients developed in high‐speed liquid composite molding may produce hydrodynamically induced preform deformation. Such deformation away from the mold wall is expected to open new flow channels, creating edge effects and rendering mold filling calculations based on Darcy's law inaccurate. A simple model is proposed to assess the conditions where preform deformation is expected to play a dominant role during mold filling. The model includes preform material properties such as stiffness, permeability, and clamping pressure, as well as the process injection pressure and the mold geometry. The utility of the model is illustrated for two reinforcement materials, a random mat and a 3‐dimensional woven fabric.
Critical issues in model verification for the resin transfer molding process
Authors: Calhoun D. R. , Yalvaç S. , Wetters D. G. , Raeck C. A. 
Published: April 2004

AbstractThis study investigates the components of a constant injection rate resin transfer molding system and discusses critical issues of each component from an experimental view. Also included are temperature and pressure data of independently designed mold flow experiments performed at The Dow Chemical Company. The experiments in this study included isothermal one‐dimensional flow with line gating and end venting, isothermal two‐dimensional flow with converging flow and center venting, and two different resin systems. Accurate and precise permeability measurements of the fiber preform continue to be the core of the issue. Deformation, contour, or overlap of the fiber preform can cause minor variation in local permeability, which, when compared with the bulk permeability, can vary the injection pressures up to an order of magnitude. Further, local dimensional changes in the fiber preform (i.e., overlap, contour, or edge‐effect) can form a channel for racetracking of the resin during injection. The inability to accurately predict a priori the extent of racetracking reduces modeling efforts to a demonstration of the flow trend.
Permeability measurement and flow simulation through fiber reinforcement
Authors: Gauvin R. , Trochu F. , Lemenn Y. , Diallo L. 
Published: April 2004

AbstractContinuous fiber reinforced polymer composites can be produced by the injection of a reactive fluid into a mold with preplaced reinforcement. Mold filling modeling softwares such as our RTMFLOT software are being developed to help design and production engineers meet their requirements for part production. The utilization of accurate permeability values is an absolute necessity for relevant mold filling simulation. This paper presents permeability results for several reinforcements. Experimental techniques being used to measure the permeability are also discussed. Several points are highlighted and suggestions are made to help the investigator in the search for reliable permeability data.
Sheet extrusion of microcomposites based on thermotropic liquid crystalline polymers and polypropylene
Authors: Handlos A. A. , Baird D. G. 
Published: April 2004

AbstractThis work is concerned with the extrusion of sheets from pellets of polypropylene (PP) containing pregenerated microfibrils of thermotropic liquid crystal polymers (TLCPs), referred to as microcomposites. The TLCPs used were HX6000 and Vectra A950. The microcomposites are produced by drawing strands of PP and TLCPs generated by means of a novel mixing technique and pelletizing the strands. The work was undertaken in an effort to improve on the properties for in situ composites in which the TLCP fibrils are generated in contractions in the die and the subsequent drawing step. In situ composites usually exhibit highly anisotropic mechanical properties and the properties do not reflect the full reinforcing potential of the TLCP fibers. Factors affecting the mechanical properties of the composite sheets considered include the effect of in situ composite strand properties and TLCP concentration. In addition, the properties of the extruded sheets are compared to those of microcomposites processed by means of injection molding. It is shown that the sheets produced using microcomposites have a good balance between the machine and transverse direction properties (ratios of these properties ranging from 0.8 to 1.2) and those properties compare well to those obtained by processing microcomposites in injection molding. The tensile modulus of the composite sheets increases with increasing in situ composite strand modulus. The moduli of the 20 wt% Vectra A950 and HX6000 composites are about equal to the modulus of 20 wt% glass reinforced PP (about 2.1 GPa), while the tensile strength of the TLCP reinforced composites is 28% lower than that of the glass reinforced PP. Furthermore, it is shown that the tensile modulus of the 10 wt% TLCP composites approach the predictions of composite theory, while at 20 and 30 wt% TLCP negative deviations from the predictions of composite theory are seen. Finally, it is concluded that the properties of the sheets produced through the extrusion of microcomposites may be further improved by improving the modulus of in situ composite strands and reducing the TLCP fiber diameter.
Modeling of void formation and removal in liquid composite molding. Part I: Wettability analysis
Authors: Patel N. , Lee L. James 
Published: April 2004

AbstractThis two‐part paper focuses on the characterization and simulation of two important molding defects in liquid composite molding—poor wetting and void formation. Part I analyzes resin‐fiber wettability. This involved characterization of various liquids/resins and fiber filaments/fiber mats by using wicking test and capillary pressure measurement. Methodology to quantify capillary pressurewettability relationships was developed. It was found that the Leverett J function can correlate capillary pressure‐saturation relationships for fiber reinforcements with various porosities and fiber architecture.
Modeling of void formation and removal in liquid composite molding. Part II: Model development and implementation
Authors: Patel N. , Lee L. James 
Published: April 2004

AbstractThe objective of this Part II is to model void formation and their removal in LCM. From the micro‐scale flow pattern and void formation mechanisms observed by flow visualization, a phenomenological model based on the multi‐phase Darcy's law was developed to simulate the void formation during LCM mold filling. Results from Part I were used to determine several important parameters of the model. The model was able to predict macro‐void fractions with flow rates and liquid properties. A criterion for the movement of trapped voids was also developed.
Bulge forming of braided thermoplastic composite tubes under axial compression and internal pressure
Authors: Manabe Ken‐Ichi , Ozaki Jun‐Ichi 
Published: April 2004

AbstractIn this study, the bulge forming of fiber reinforced thermoplastic (FRTP) composite braided tubes was studied as a new forming technique utilizing fiber orientation rearrangement (the trellis effect) at temperatures near the matrix melting point. It is shown that free bulge forming with the trellis effect can easily result in high expansion without buckling only by axial compression. This is when the stress of the matrix is small enough to rearrange the fiber orientation of the braid. To improve the surface quality and dimensional accuracy, bulge forming with closed dies and internal pressure was also examined experimentally. The appropriate conditions for axial penetration and internal pressure are established. The kinematics of braid is also considered, and calculations from the model are evaluated from experiments. In addition, the kinematic state of braid after deformation is simulated by calculation from the geometric braid model. It is found that the “normalized profile” of the bulged tube does not change during the process and the thickness of the matrix depends on changing fiber orientation.
Material characterization for flow modeling in structural reaction injection molding
Authors: Chick J. P. , Rudd C. D. , Van Leeuwen P. A. , Frenay T. I. 
Published: April 2004

AbstractTo support mold filling studies in liquid composite molding, a chemorheological model has been developed that describes the viscosity of an amine‐cured epoxy resin of the type used in structural RIM. The model predictions are compared with results from Monte Carlo network simulations and DSC data. The viscosity model is then used to estimate the principal in‐plane permeabilities of fiber reinforcements using data taken directly from an SRIM process. The experimental method, based on a radial solution to Darcy's law, yields both the wetting and wetted permeabilities. The method has been demonstrated for two plane random reinforcements and indicates negligible difference between wetted and wetting permeabilities at the flow rates considered. The results compare favorably with existing data from radial and rectilinear flow bench rigs.
Concurrent methods for permeability measurement in resin transfer molding
Authors: Ferland Pierre , Guittard Dominique , Trochu François 
Published: April 2004

AbstractThe numerical simulation of the resin transfer molding process (RTM) requires knowledge of the physical properties of the fibrous material. In particular, the resistance to the resin flow is measured by the permeability of the preform in the mathematical model of Darcy's law. A concurrent method for low‐cost permeability estimation is proposed. The method uses a rectangular mold for the numerical determination of the principal permeabilities. The experimental data include a built‐in correlation with Darcy's law and allow an estimation of both experimental and numerical errors. Since the experimental procedure can introduce a significant uncertainty on the estimated permeability, practical considerations are pointed out and some relevant parameters such as the minimum injected length and maximum injection pressure are introduced to increase the reliability of permeability measurements.
Experimental investigation of flow‐induced microvoids during impregnation of unidirectional stitched fiberglass mat
Authors: Rohatgi V. , Patel N. , Lee L. James 
Published: April 2004

AbstractThe complexity of the resin injection step in liquid composite molding (LCM) processes, such as resin transfer molding (RTM) and structural reaction injection molding (SRIM), often results in flow‐induced defects such as poor fiber wetting and void formation. These defects have a deleterious effect on the mechanical properties of composites. In this work, high resolution video‐assisted microscopy was used for in situ observation of flow‐induced interstitial voids or microvoids formed inside the fiber tows during mold filling. Flow visualization experiments were carried out with different liquids to better understand the microscale flow behavior that led to the formation of microvoids for flow both along and normal to the fiber tows. Microvoid formation was correlated to the modified capillary number, Ca#* = μν/γcos(θ). The study revealed that for axial flow, microvoids were formed at Ca#* > 10−3. For transverse flow, microvoids were formed at an even lower capillary number. ∼ 10−4. Once formed, microvoids were difficult to purge and remained trapped even after bleeding the liquid at much higher flow rates than those at which they were formed.
Simulation of the effects of thermal history on the morphology of thermoplastic composites
Authors: Deporter J. K. , Baird D. G. 
Published: April 2004

AbstractThis paper concerns the simulation of the development of the degree of crystallinity and the size of spherulites that arise during the cooling of a slab of a semicrystalline polymer reinforced with long, continuous carbon fibers. This situation is commonly found during the processing of semicrystalline thermoplastic composites. Whereas published attempts at simulating this process have treated the composite as a continuum, and thereby used mass averaged physical properties (such as thermal conductivity, density, and specific heat), we use a quasicontinuum approach in which we consider the properties of the matrix and fiber separately. Once a temperature distribution is calculated using the continuum approach, the finite element method is applied locally at various points in the slab to calculate the degree of crystallinity and the size of the developing spherulites. This is done by using the Avrami equation and the Hoffman and Lauritzen radial growth equation. The degree of crystallinity and the spherulite size are predicted as a function of fiber spacing and packing geometry, and the predictions are in good agreement with experimental results obtained on poly(phenylene sulfide)/carbon fiber composites. The advantages of our approach over the continuum approach is that a relatively accurate prediction of the spherulite size is possible owing to constraints imposed by the fiber on the spherulitic growth.