bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of the steel core of composite squirrel cage rotor on motor performance
Authors: Chang Seung Hwan , Lee Dali Gil
Published: April 2004

Since the critical whirling vibration frequency of high speed built‐In type motor spindle systems is dependent on the rotor mass of the built‐In motor and the spin‐die specific bending modulus, the rotor and the shaft were manufactured using magnetic powder contained epoxy and high modulus carbon fiber epoxy composite, respectively. In order to enhance the magnetic flux of the composite squirrel cage rotor of an AC induction motor, a steel core was inserted into the composite rotor. The motor parameters of the developed composite rotor system were obtained from the no‐load and blocked rotor tests and the effect of thickness of the steel core on the motor performance was investigated. From the magnetic analysis, the optimal steel core size for the dynamic characteristics of the rotor system mounted on the carbon fiber epoxy composite spindle was determined.
Fundamental investigation of cure‐induced microcracking in carbon fiber/bismaleimide cross‐ply laminates
Authors: Lincoln Jason E. , Morgan Roger J. , Shin E. Eugene
Published: April 2004

Transverse microcracks are present in carbon fiber/bismaleimide (BMI) cros: composite laminates composed of 4, 4′‐bismaleimidodiphenylmethane (BMPM)/diallyl bisphenol A (DABPA) matrices after standard cure and fabrication condit and grow in width upon subsequent postcure. This investigation characterizes cure‐induced microcracking in terms of the critical fundamental macroscopic croscopic, and molecular damage mechanisms and thresholds, and a cure cycle modification that prevents microcrack formation under standard processing conditions tions for [0°/90°]s laminates is examined. A unique in‐situ technique is utilized which cure of the laminate is performed inside the chamber of an environim scanning electron microscope (ESEM), allowing for (i) physical observation of microcrack crack growth and formation mechanisms and (ii) characterization of microcracking onset time‐temperature thresholds. The cure cycle modification that prevents microcracking is an extended initial cure time at 177°C prior to higher temperature; cure regimes. Effects of this modification are examined through network structure property‐processing interrelationships by way of (i) dynamic mechanical analysis (DMA), (ii) optical and electron microscopy, (iii) differential scanning calorimetry (DSC), and (iv) our previous work on carbon fiber/bismaleirnide composites. The aforementioned analysis it was concluded that an extended initial cure time 177°C prior to higher temperature cure steps prevents microcracking under standard; fabrication postcure conditions for [0°/90°]s laminates; no microcracking observed until an additional postcure of 6 h at 300°C. This microcrack resist was independent of initial BMPM:DABPA monomer stoichiometry for the monomer ratios examined and associated with an improved fiber‐matrix interface and lower composite residual stress.
Solid state bonding of graphite/thermoset composites via interchain transesterification reaction (ITR)
Authors: López Alfonso , Economy James
Published: April 2004

Thick section composite laminates are expensive and difficult to manufacture because of problems with porosity, large reaction exotherms from epoxies and residual strains. The copolyester thermosets described here can eliminate these problems. Through interchain transesterification reactions, individually cured prepreg plies of graphite reinforced copolyester can be bonded with each other in the solid state. ITR bonding is shown to produce well‐consolidated laminates with less than 2% void volume and mechanical properties comparable to those of current high‐end polymer matrix composites. DMA testing showed the glass transition to begin at 190°C for a 45% fiber volume fraction composite. Tensile testing of 55% fiber volume composites at room temperature showed modulus, strength and elongation to failure averages of 105.4 GPa, 1.02 GPa and 1.0% respectively.
Modification of thermosetting resins and composites through preformed polymer particles: A review
Authors: Hayes Brian S. , Seferis James C.
Published: April 2004

A review is presented that focuses on preformed particle modification of high performance thermosetting resins and composite systems. The modifiers reviewed consist of thermoplastic and rubber preformed particles with no size limitations. Both organic and inorganic preformed polymer particles are considered but not glass or hollow spheres. In this text, preformed particles are defined as those which do not require phase separation and remain in the shape in which they were added to the neat resin or composite. Therefore, these particles may be developed prior to the resin formulation and then added to the thermosetting resin or developed in situ (during resin formulation) before the resin is catalyzed or cured. This technical review of preformed particle modification of thermosetting resins and composite systems summarizes the utilization of these materials and their performance.
The influence of fiber surface modification on the mechanical properties of coir‐polyester composites
Authors: Rout J. , Tripathy S. S. , Misra M. , Mohanty A. K. , Nayak S. K.
Published: April 2004

Coir, an important lignocellulosic fiber, can be incorporated in polymers like unsaturated polyester in different ways for achieving desired properties and texture. But its high level of moisture absorption, poor wettability and insufficient adhesion between untreated fiber and the polymer matrix lead to debonding with age. In order to improve the above qualities, adequate surface modification is required. In our present work, fiber surface modification was effected through dewaxing, alkali (5%) treatment, aqueous graft copolymerization of methyl methacrylate (MMA) onto 5% alkali treated coir for different extents using CuSO4 – NaIO4 combination as an initiator system and cyanoexhylation with a view to improve the mechanical performance of coir‐polyester composites. Mechanical properties like tensile strength (PS), flexural strength (ES) and impact strength (IS) of the composites as a function of fiber loading and fiber surface modification have been evaluated. Composites containing z5 wt% of fiber (untreated) improved tensile and flexural strength by 30% and 27% respectively in comparison to neat polyester. The work of fracture (impact strength) of the composite with 25 wt% fiber content was found to be 967 J/m. The elongation at break of the composites exhibits an increase with the introduction of fiber, All types of surface modification result In improved mechanical properties of the composites. Significant improvement in mechanical strength was also observed for composites prepared from 5% PMMA grafted fiber.
Investigation of unsaturated flow in woven, braided and stitched fiber mats during mold‐filling in resin transfer molding
Authors: Slade J. , Pillai K. M. , Advani S. G.
Published: April 2004

In Resin Transfer Molding (RPM), which is a process to manufacture polymer composites, the impregnation of fibrous reinforcement In the form of mats by a thermosetting resin is modeled as the flow of a Newtonian liquid through a single length‐scale porous medium. While this approach is sufficiently accurate for random fiber‐mats, it can lead to appreciable errors when applied to woven, braided, or stitched fiber‐mats that contain two length scales. This work investigates the primary factors governing the isothermal unsaturated flow through such dual‐scale porous media. Two studies were conducted to better understand this phenomenon: the first experimenatally investigated the flow, while the second theoretically modeled the flow and identified important parameters affecting such a flow with the help of dimensionless analysis. In the first study, one‐dimensional constant injection rate experiments were performed using various fiber mats. The unsaturated flow behavior of various mats was characterized using a constant “sink” term in the continuity equation. Results indicated that for a given fiber‐mat, the magnitude of the sink effect was a function of the capillary number. In the second study, a numerical model was developed to describe flow through dual‐scale preforms in which the two flow domains, the inter‐ and intra‐tow regions, were coupled. We identified a dimensionless number called the sink effect index ψ that characterizes the magnitude of liquid absorption by the tows and is a function of the relative resistance to flow in the tow and inter‐tow regions, and the packing density of the tows. The parametric study of this index with the help of numerical simulations reveals its influence on the flow and identifies the distinct transient and steady‐state flow regimes.
Prediction of failure and fracture mechanisms of polymeric composites using finite element analysis. Part 2: Fiber reinforced composites
Authors: Ghassemieh E. , Nassehi V.
Published: April 2004

A robust finite element scheme for the micro‐mechanical modeling of the behavior of fiber reinforced polymeric composites under external loads is developed. The developed model is used to simulate stress distribution throughout the composite domain and to identify the locations where maximum stress concentrations occur. This information is used as a guide to predict dominant failure and crack growth mechanisms in fiber reinforced composites. The differences between continuous fibers, which are susceptible to unidirectional transverse fracture, and short fibers have been demonstrated. To assess the validity and range of applicability of the developed scheme, numerical results obtained by the model are compared with the available experimental data and also with the values found using other methods reported in the literature. These comparisons show that the present finite element scheme can generate meaningful results in the analysis of fiber reinforced composites.
Inferring the degradation of pultruded composites from dynamic nonlinear resonance measurements
Authors: Van Den Abeele K. , Carmeliet J. , Van De Velde K.
Published: April 2004

The Chemical resistance of pultruded polyester composites to various chemical immersion solutions is investigated as a function of the exposure time, and the observations from static tests are compared with the results from nonlinear dynamic vibration experiments. The mechanical properties were measured according to ASTM standards, both in flexural and tensile tests. Barcol hardness and sorption measurements provide complemntary information. In addition, a novel nondestructive (NDE) method, called Single Mode Nonlinear Resonance Acoustic Spectroscopy (SIMONRAS), was applied to measure the linear and nonlinear dynamical properties of the samples as a funtion of exposure time. This new NDE method focuses on the strain amplitude dependence of the resonance frequency while driving a sample at relatively low excitation levels. The obtained relative frequency shift is a measure of the internal microstructural properties of the material. The correlation between this nonlinearity parameter and the mechanical properties is extremely good, which implies that the SIMONRAS technique can be applied to predict the chemo‐mechanical degradation of composites in a nondestructive manner.
Mechanical properties and morphology of flax fiber reinforced melamine‐formaldehyde composites
Authors: Hagstrand P.‐O. , Oksman K.
Published: April 2004

The mechanical performance of natural fiber reinforced polymers is often limited owing to a weak fiber‐matrix interface. In contrast, melamine‐formaldehyde (MF) resins are well known to have a strong adhesion to most cellulose containing materials. In this Paper, nonwoven flax fiber mat reinforced and particulate filled MF composites processed by compression molding are studied and compared to a similar MF composite reinforced with glass fibers. Using flax instead of glass fibers has a somewhat negative effect on tensile performance. However, the difference is relatively small, and if density and material cost are taken into account, flax fibers become competitive. Tensile damage is quantified from the stiffness reduction during cyclic straining. Compared to glass fibers, flax fibers generate a material with a considerably lower damage rate. From scanning electron microscopy (SEM), it is found that microcracking takes place mainly in the fiber cell walls and not at the fiber‐matrix interface. This suggests that the fiber‐matrix adhesion is high. The materials are also compared using dynamic mechanical thermal analysis (DMTA) and water absorption measurements.
A thermoviscoelastic analysis of process‐induced internal stresses in thermoplastic matrix composites
Authors: Sunderland Paul , Yu Wonjae , Månson Jan‐Anders
Published: April 2004

A numerical tool for predicting the evolution of internal and residual stresses during the processing of thermoplastic matrix composites has been developed. Based on a finite element formulation, the model accounts for the anisotropy, vis‐coelasticity and heterogeneity of the materials and represents mechanisms of both stress generation and stress relaxation. The viscoelastic properties are described by a linear thermoviscoelastic formulation. The model allows the buildup of stresses during processing to be monitored, in particular when the material is cooling through its transition temperatures, and enables the prediction of stress release and the resulting part waipage on demolding. Its use is demonstrated for unidirectional and crossply polyetherimide/glass fiber (PEI/GF) laminates processed by compression molding, and the influence of cooling conditions on stress levels is shown.
Extrusion conditions and properties of vapor grown carbon fiber reinforced polypropylene
Authors: Kuriger Rex J. , Alam M. Khairul
Published: April 2004

Vapor grown carbon fiber (VGCF) is a new and inexpensive carbon fiber produced by vapor deposition of hydrocarbons on metal catalysts. The ability to fabricate VGCF reinforced thermoplastic composites by extrusion provides the potential to exploit VGCF into new commercial markets. This study investigates the extrusion conditions and properties of VGCF reinforced polypropylene. Extrusion was carried out using a Leistritz twin‐screw extruder. Polypropylene reinforced with 0% to 12.5% volume fraction VGCF was extruded successfully at temperatures ranging from 215°C to 250°C. The extrusion pressure increased and the flow rate decreased as the percentage of fiber was increased. Increases in tensile strength and modulus were observed by the addition of VGCF. However, the void content of the composite samples increased with fiber content.
Dynamic stress/strain response of the interphase in polymer matrix composites
Authors: Tanoglu M. , McKnight S. H. , Palmese G. R. , Gillespie J. W.
Published: April 2004

The interphases of various sized E‐glass‐fiber/epoxy‐amine systems were tested at displacement rates in the range of 230 to 2450 fxm/sec using a new experimental technique (dynamic micro‐debonding technique). The fiber systems include unsized, epoxy‐amine compatible sized, and epoxy‐amine incompatible sized glass fibers. A data reduction scheme was developed to relate the force vs. displacement response obtained from the dynamic micro‐debonding technique to interphase shear stress/strain response. The stress/strain curves and interphase shear modulus values were obtained from these composite systems under average shear strain rates (ASSR) in the range of 215–3278 (1/s). The results showed that the magnitude of the interphase shear modulus was sizing and strain rate dependent. In all cases, the shear modulus was found to be more compliant than the bulk matrix. The two sized fiber systems exhibited the highest strain rate sensitivity, with modulus increasing about threefold over the range studied. In addition, the rate dependent behavior of the model interphase materials were determined using the dynamic mechanical analysis (DMA) technique. The model interphase materials closely resemble the interphase that forms on unsized and compatible sized fibers. Master curves relating the flexural storage modulus to strain rate were constructed based on the time‐temperature superposition principle from DMA frequency sweep measurements. The DMA measured results are consistent with the dynamic micro‐debonding test results, providing confidence in the test method as a reliable technique for characterizing the high strain rate properties of the interphase in composites.
Studies on the preparation and mechanical properties of esthetic polymeric dental restoratives using silane treated silica microfiller via freeze‐drying
Authors: Kim Ohyoung , Shim W. Jaewoo
Published: April 2004

Polymeric dental restorative composites were prepared using silica filler where the surface was treated with γ‐methacryloxypropyltrimethoxysilane and decanted solvents by the freeze‐drying method. This treatment improved the miscibility of the filler with 2,2′‐bis‐[4‐(methacryloxy‐2‐hydrbxypropoxy)‐phenyl]‐propane/triethyl‐eneglycoldimethacrylate resin matrix and enhanced the esthetic properties of the composite. Diametral tensile strength (DTS) and flexural strength (FS) of the dental composite were measured, and the effect of drying methods in the surface treatment of filler on the mechanical properties of the composite was also investigated. Dental restorative composites prepared by the freeze‐drying method showed substantially higher DTS and FS values than those prepared by the conventional heat‐drying method. This resulted in increasing the loading percentage of filler in the resin matrix, and thereby, DTS values were increased dramatically. Dispersion of silica filler in the resin matrix and surface characteristics were examined by scanning electron microscopy. Various esthetic grades of dental composites were successfully prepared using iron oxide pigments, and its Hunter L. a. b. values of vita color‐shade were also investigated.
Flow‐induced fiber orientation in injection molded fit fiber reinforced polypropylene
Authors: Aurich T. , Mennig G.
Published: April 2004

A 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

Sheet 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

Ethylene‐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

A 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

Based 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

A 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

An 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

Knowledge 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

Large 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

This 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

Continuous 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

This 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

This 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

The 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

In 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

To 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

The 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

The 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

This 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.
Multilayer plug flow modeling of the fast stamping process for a polypropylene/glass fiber composite
Authors: Leterrier Y. , G'Sell C.
Published: April 2004

The isothermal compression at 200°C of a polypropylene/glass fiber composite was investigated in both axisymmetric and unidirectional flows. The overall stress/strain behavior at various compression strain rates was recorded and the induced orientation of the fibers is investigated. It is shown that, in the high speed range, the macroscopic flow process controlled by both the viscous extension and the relative sliding of parallel fibrous layers. The evolution of the compression force is modeled as the sum of a viscous resistance and an interlaminar friction.
Physico‐Chemical and micromechanical analysis of the interface in a poly(phenylene sulfide)/glass fiber composite—a microbond study
Authors: Gonon L. , Momtaz A. , Van Hoyweghen D. , Chabert B. , Gérard J.‐F. , Gaertner R.
Published: April 2004

The glass fiber/PPS composite has excellent thermal and chemical properties. The main disadvantage of the composite is its poor mechanical resistance to impact. To improve this property, the fibers were coated with a new type of sizing. The equired characteristics for this sizing is to create strong interactions between the PPS matrix and the glass fiber surface. The ability of the sizings to improve the glass/PPS adhesion has been assessed by the microbond technique. An inconvenience of this technique is the difficulty in defining a parameter that is characteristic of the interfacial adhesion. The objective of this publication is to demonstrate that a plastic flow of the PPS matrix around the fiber leads to a uniform shear strength. The adhesion between these two materials can therefore be obtained by the mean interfacial shear strength.
Structuring of binary PP/PA‐6 blends and ternary PP/PA‐6/GF blends
Authors: Benderly D. , Siegmann A. , Narkis M.
Published: April 2004

Morphological development under shear flow conditions for binary polypropylene (PP)‐polyamide‐6 (PA‐6) and ternary PP‐PA‐6‐glass fiber blends has been investigated. The shear viscosity was determined at several temperatures, and the blend morphology was investigated as a function of shear rate and temperature. Blend morphology perpendicular and parallel to the flow direction was examined to give a complete description of the structuring of the polymer blend during flow. For blends containing a PA‐6 matrix, the glass fiber (GF) and minor PP phase are separately dispersed within the matrix, and the morphological development during flow is similar for binary and ternary blends. However, for blends containing a PP matrix, the GF are mainly encapsulated by the minor PA‐6 phase. This encapsulated morphology reduces the effective amount of PA‐6 dispersed within the matrix, and the development of an “interlayer slip” morphology, typical of PP/PA‐6 blends, is reduced. These differing ternary blend structures have implications for the shear viscosity, and its correspondence to a rule of mixtures prediction. For PA‐6–rich blends, the actual viscosity is lower than the predicted, owing to slippage between the PP dispersed phase and the PA‐6 matrix. However, in PP‐rich ternary blends, the experimental viscosity data matches a modified rule of mixtures prediction. The addition of PA‐6 to a PP/GF system does not increase the amount of “slippage” sites, owing to the encapsulated morphology. Therefore, the shear viscosity is not reduced by PP‐PA‐6 slippage.
Stress distribution around inclusions, interaction, and mechanical properties of particulate‐filled composites
Authors: Pukánszky Béla , Vörös György
Published: April 2004

Stress analysis was carried out to determine the stress distribution around particles in particulate‐filled composites. The effect of interacting stress fields was also taken into account. At large filler contents, interacting stress fields compensate for the effect of stress concentration. The solutions were introduced into the Von Mises criterion for yielding. The composition dependence of tensile yield stress was determined by using different boundary conditions and averaging techniques. An analytical expression was derived that predicts particle size and adhesion dependence of the yield stress. The analysis shows that large particles and weak interaction lead to debonding. In the case of strong adhesion, the dominating micromechanical deformation process is the shear yielding of the matrix. In such cases, particle size dependence can be explained with the effect of interfacial interactions, which lead to the formation of an interphase. The dominating deformation mechanism is determined by particle characteristics and adhesion of the components. The predictions of the analysis are in good agreement with experimental observations.
A comparison of short glass fiber reinforced polypropylene plates made by conventional injection molding and using shear controlled injection molding
Authors: Hine P. J. , Duckett R. A. , Ward I. M. , Allan P. S. , Bevis M. J.
Published: April 2004

This paper describes a comparison of the fiber orientation structures and resulting elastic properties of samples of short glass fiber filled polypropylene made by conventional injection molding and by the SCORIM (Shear Controlled Orientation in Injection Molding) process developed at The University of Brunel. The 3D fiber orientation distributions of the composites were measured using a unique transputer based image analysis system developed at The University of Leeds. The mechanical properties of the samples were characterized using an ultrasonic velocity technique, which allows a full set of elastic constants to be determined for each material. The link between fiber orientation distributions and measured elastic properties was then investigated using theoretical models developed in this laboratory.
Crack growth and fracture behavior of fabric reinforced polymer composites
Authors: Chellappa V. , Jang B. Z.
Published: April 2004

The objective of this study is to understand and characterize crack deflection and sub‐crack growth in fabric laminate composites. The theory of crack digression based on the Cook‐Gordon mechanism of crack blunting and the criterion developed by Kendall were used to study the crack propagation phenomenon. A simple approach has been developed to evaluate the cohesive and adhesive fracture energies, which play a vital role in the study of strength and toughness of the fabric laminate composites. The effects of strain rate and quasi‐static crack velocity on these energy values were identified. This study explored the possibility of selftoughening in an otherwise brittle composite system. Two competing mechanisms have been identified that control crack propagation in fabric laminate composites.