bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanical and rheological properties of HDPE/graphite composite with enhanced thermal conductivity
Authors: Wang Qi , Gao Jun , Wang Ru , Hua Zhengkun
Published: April 2004

Having been treated with coupling agent and pan‐milling, graphite is incorporated into HDPE to make a HDPE/graphite composite with enhanced thermal conductivity as well as good mechanical properties and processibility. This paper focuses on the study of mechanical properties, thermal stability and rheological behavior of HDPE/graphite composite. The experimental results show that with increase of the graphite content, Young's modulus of HDPE/graphite increases and the elongation at break and impact strength decrease. However, when the graphite content is 35% in HDPE/graphite, the elongation at break and impact strength still remain 22.4% and 85.8J/m. respectively. Also, the yield strength increases with the increase of the graphite content, and reaches the maximum at 55% graphite content, and reduces afterwards. The crystallization temperature and thermal stability of HDPE/graphite increase with the increase of the graphite content. The melt viscosity of the filled HDPE remains almost unchanged, but the shear sensitivity increases, and the temperature sensitivity decreases with the increase of the graphite content. By optimizing the experimental conditions, a HDPE/graphite composite with fairly good comprehensive properties such as enhanced thermal conductivity and stability, good mechanical properties, and processability could be prepared, which has potential application in the field of heat transfer.
Comparison of mechanical performance and fracture behavior of gelatin composites reinforced with carbon fibers of different fiber architectures
Authors: Wan Y. Z. , Wang Y. L. , Luo H. L. , Dong X. H. , Cheng G. X.
Published: April 2004

Gelatin‐based composites reinforced, respectively, with continuous carbon fibers, short carbon fibers, plain woven carbon fibers, and carbon fiber felt were investigated. Tensile and shear strengths, and their changes with fiber volume fraction (Vf) of these four composites were compared. It was demonstrated that at all fiber levels, the composite containing continuous carbon fibers showed the largest strength, while the composite reinforced with carbon fiber felt exhibited the lowest strength of the four composites. The above results were analyzed by comparing the fracture surfaces of the four composites. SEM confirmed the great differences in fracture surfaces for composites of different fiber architectures. The presence of a large number of pores in the CF/Gel composite was responsible for its lowest strength, and cracks within fiber tows caused the lower strength of the CW/Gel composite when compared to its CL/Gel counterpart. It was suggested that fiber architecture exerted a great effect on composite performance and the effect was dependent on the nature of the matrix material.
Optimal curing for thermoset matrix composites: Thermochemical considerations
Authors: Li Min , Zhu Qi , Geubelle Philippe H. , Tucker Charles L.
Published: April 2004

A design sensitivity analysis is used to optimize the applied wall temperature vs. time in autoclave curing for thermoset matrix composites. The calculation minimizes the cure time and obeys a maximum temperature constraint in the composite. The transient, coupled thermal and cure problem is solved by a finite element method. Design sensitivity information is extracted efficiently from this primal analysis, based on an analytical, direct differentiation approach. The sensitivities are then used with gradient‐based optimization techniques to systematically improve the curing process. The optimal cure cycles for different numbers of temperature dwells may be similar (for a 2 mm thick part) or very different (for a 4 cm thick part), depending on the nature of the problem. In the latter case a large reduction of cure time is obtained when a three‐dwell cure cycle is used, and the optimizer has more flexibility to adjust the cure cycle. This systematic optimization approach provides a powerful and practical means of optimizing composite manufacturing processes.
Factors affecting the joint strength of ultrasonically welded polypropylene composites
Authors: Liu Shih‐Jung , Chang I‐Ta , Hung Shiu‐Wan
Published: April 2004

Ultrasonic welding of thermoplastic composites has become an important process in industry because of its relatively low cost and resultant high quality joints. An experimental study, based on the Taguchi orthogonal array design, is reported on the effect of different processing factors on the joint strength of ultrasonically welded composites, including weld time, weld pressure, amplitude of vibration, hold time, hold pressure, and geometry of energy director. Three materials were used in the study: virgin polypropylene, and 10% and 30% glass‐fiber filled polypropylene composites. Experiments were carried out on a 2000‐Watt ultrasonic welding unit. After welding, the joint strength of the composites was determined by a tensile tester. For the factors selected in the main experiments, weld time, geometry of energy director and amplitude of vibration were found to be the principal factors affecting the joint property of ultrasonically welded thermoplastic composites. Glass‐fiber filled polymers required less energy for successful welding than the non‐filled polymer. The joint strength of welded parts increased with the fiber content in the composites. In addition, a triangular energy director was found to weld parts of the highest strength for virgin polypropylene and 10% glass‐fiber filled polypropylene composites, while a semi‐circular energy director was found to weld the highest strength parts for 30% glass‐fiber filled composites.
Factorial design approach applied to electrically and thermally conductive nylon 6,6
Authors: King Julia A. , Tucker Kenneth W. , Meyers Jeffrey D. , Weber Erik H. , Clingerman Matthew L. , Ambrosius Kip R.
Published: April 2004

Increasing the thermal and electrical conductivity of typically insulating polymers, such as nylon 6,6, opens new markets. A thermally conductive resin can be used for heat sink applications. An electrically conductive resin can be used in static dissipative and Electromagnetic Interference/Radio Frequency Interference shielding applications. This research focused on performing compounding runs followed by injection molding and testing (tensile properties, volumetric electrical resistivity, and through‐plane thermal conductivity) of carbon filled nylon 6,6. The four carbon fillers investigated included a PAN‐based carbon fiber (milled, 200μ long), an electrically conductive carbon black, vapor grown graphitic nanotubes, and Thermocarb (high quality synthetic milled graphite). Formulations were produced and tested that contained varying amounts of a single carbon filler. Combinations of fillers were also investigated via conducting half of a 24 factorial design. It was determined that Thermocarb has the largest effect on the thermal conductivity. Increasing Thermocarb increases thermal conductivity. For conductive resins containing only a single filler type, nanotubes caused the electrical resistivity (ER) to decrease the most. For the half fraction factorial design formulations that contain at least one filler type at the higher level, the ER of the conductive resin ranged from 0.1 to 0.3 ohm‐cm.
The effect of temperature and loading rate on the mode II interlaminar fracture properties of a carbon fiber reinforced phenolic
Authors: Berger L. , Cantwell W. J.
Published: April 2004

The combined effect of varying loading rate and test temperature on the mode II Interlaminar fracture properties of a carbon fiber reinforced phenolic resin has been investigated. End notch flexure tests at room temperature have shown that this composite offers a relatively modest value of GIIcNL at non‐linearity and that its interlaminar fracture toughness decreases with increasing loading rate. As the test temperature is increased, the quasistatic value of GIIcNL increases steadily and the reduction in GIIcNL with loading rate becomes less dramatic. At temperatures approaching the glass transition temperature of the phenolic matrix, the interlaminar fracture toughness of the composite begins to increase sharply with crosshead displacement rate. A more detailed understanding of the effect of varying the test conditions on the failure mechanisms occurring at the crack tip of these interlaminar fracture specimens has been achieved using the double end notch flexure (DENF) geometry.
Electrostatic discharge properties of knitted copper wire/glass fiber fabric reinforced polypropylene composites
Authors: Cheng K. B. , Ramakrishna S. , Lee K. C.
Published: April 2004

This paper presents a study on the development conductive knitted fabric reinforced thermoplastic composites, with the intention to use them in electrostatic discharge applications. Conductive knitted fabric composites are made using polypropylene as the matrix material, glass fibers as the reinforcement, and copper wires as the conductive fillers. To facilitate knitting of stiff copper wires and glass fibers, uncommingled yarns comprising copper wires, glass fibers, and polypropylene fibers are produced using a hollow spindle spinning method. Several kinds of conductive composite laminates are made by changing the fabric knit structure, stitch density, and the composition of yarns. The electrostatic discharge (ESD) attenuation of various laminates is measured at voltage potentials 8kV and 12 kV. The variations of ESD properties of composite laminates with the fabric knit structure, stitch density, and the amount of copper are described.
Microwave and conventional curing of thick‐section thermoset composite laminates: Experiment and simulation
Authors: Thostenson Erik T. , Chou Tsu‐Wei
Published: April 2004

In conventional processing, thermal gradients cause differential curing of thick laminates and undesirable outside‐in solidification. To reduce thermal gradients, thick laminates are processed at lower cure temperatures and heated with slow heating rates, resulting in excessive cure times. Microwaves can transmit energy volumetrically and instantaneously through direct interaction of materials with applied electromagnetic fields. The more efficient energy transfer of microwaves can alleviate the problems associated with differential curing, and the preferred inside‐out solidification can be obtained. In this work, both microwave curing and thermal curing of 24.5 mm (1 inch) thick‐section glass/epoxy laminates are investigated through the development of a numerical process simulation and conducting experiments in processing thick laminates in a conventional autoclave and a microwave furnace. Outside‐in curing of the autoclave‐processed laminate resulted in visible matrix cracks, while cracks were not visible in the microwave‐processed laminate. Both numerical and experimental results show that volumetric heating due to microwaves promotes an inside‐out cure and can dramatically reduce the overall processing time.
Continuous carbon fiber polymer‐matrix composites and their joints, studied by electrical measurements
Authors: Chung D. D. L.
Published: April 2004

Continuous carbon fiber polymer‐matrix composites and their Joints, as studied by DC electrical measurements, are reviewed. The resistance gives information on the microstructure and allows the self‐sensing of strain, damage and temperature. In the case of composites with dissimilar fibers in adjacent laminae, the Seebeck effect allows temperature sensing, using the interface between laminae as a thermocouple junction. The resistance in the through‐thickness direction can be apparently negative, due to entropy‐driven electron backflow. The longitudinal resistance allows sensing of the glass transition and melting of the thermoplastic polymer matrix. The quality of composite‐composite joints obtained by adhesion or fastening, and of composite‐concrete joints obtained by adhesion, is revealed by resistance measurements.
Interface effects in elastomers reinforced by modified precipitated silica
Authors: Alberola N. D. , Benzarti K. , Bas C. , Bomal Y.
Published: April 2004

The contributions of the so‐called “interface effects” on the overall viscoelastic behavior of SBR reinforced by precipitated silica modified by model sizing agents are evaluated by using micromechanical models in a reverse mode. According to the nature of the coupling agent, two kinds of “interface effects” can be distinguished: (i) an overall change in the viscoelastic behavior of the polymer matrix, when the sizing agent is a chemical promotor acting as additional ties of the SBR network, and (ii) the formation of an actual mesophase, when direct interactions between SBR chains and silica could occur, as for example, when the coating agent of silica is an organosilane based on short aliphatic chains. With increasing the length of the aliphatic chains of the coating agent (LOS agent), some a plasticisizing effect of the polymer is detected by DSC. It can affect either the entire polymer matrix or a confined region at the close vicinity of silica aggregates. According to this assumption, the bimodal viscoelastic behavior of the LOS‐mesophase revealed by the modeling indicates that in addition to a local plasticisizing effect induced by this agent, some direct interactions could occur between silica surface and SBR constraining the mobility of rubber molecules.
Strain rate effect in the single‐fiber‐fragmentation test
Authors: Gong X. J. , Arthur J. A. , Penn L. S.
Published: April 2004

The single fiber fragmentation test (SFVU) has been widely used to characterize the interface it fiber‐reinforced polymers. The purpose of the work reported here was to determine the effect of strain rate on the fiber fragment lengths obtained in the SFFT. Three materials systems were used to make single‐fiber‐composite specimens: E‐glass fiber/polycarbonate matrix, AS4‐carbon fiber/polycarbonate matrix, and AS4‐carbon fiber/polycarbonate matrix. The fiber‐matrix adhesion in all three systems is based on physisorption rather than chemisorption. Each system was tested at strain rates ranging over four orders of magnitude. Results are reported in terms of fragment length, the dependent variable in this study, which is inversely related to the quality of the Interface. It was expected that the fragment length would show a systematic decrease with Increasing strain rate, but the expected trend was not found. Although the polycarbonate matrix exhibited rate‐dependent viscoelastic behavior typical of amorphous polymers below Tg, the fragment length at saturation did not show a statistically significant variation with strain rate for any of the three materials systems. A major contributor to the lack of observed effect was the inherent random variability associated with the SFFT; random variability in average fragment length was equal or greater than the 19% effect of rate predicted for ideal elastic systems with no debonding at the interface. In addition, considerable interfacial debonding occurred during the SFFT, not surprising for Interfaces based on physisorption alone. Debonding Interferes with transfer of applied load from matrix to fiber, and would thus interfere with transfer of the effect of rate from matrix to fiber. A tensile Impact test developed previously was also performed on single‐fiber composite specimens made from the same three materials systems. The results of the Impact tests differed from those obtained at controlled strain‐rates for only two of the materials systems.
Estimating the residual fatigue lifetimes of impact‐damaged composites using thermoelastic stress analysis
Authors: Horn Gavin P. , Mackin Thomas J. , Kurath Peter
Published: April 2004

A new experimental method is presented for quantifying impact damage and estimating the remaining fatigue lifetime of impact damaged polymer matrix composite materials. The procedure is demonstrated using composites of glass fiber reinforced polyurethane produced by injection molding and structural reaction injection molding. Thermoelastic stress analysis (TSA) was used to quantify the stress concentration associated with impact‐damage in test samples of each composite. Following impact and TSA imaging, the samples were fatigued to failure over a range of stress amplitudes. The TSA‐derived stress concentration factors were used to determine a modified stress amplitude that collapsed the impact‐fatigue data onto a master stress‐life curve. This approach provides a quantitative measure of impact damage and a practical methodology for estimating the residual fatigue lifetime of impact; damaged composites.
A model for the consolidation of warp‐knitted reinforced laminates
Authors: Rozant O. , Michaud V. , Bourban P.‐E. , Månson J.‐A. E.
Published: April 2004

A model for the consolidation of thermoplastic composites reinforced with a warp‐knitted fabric was developed. The evolution of void content during composite consolidation achieved via film stacking was related to the processing parameters and the material properties. Since the knitting process results in local variations of fiber volume fractions even within a tow, the flow mechanisms are not identical to those occurring in homogeneously dispersed fibers. Two different types of micro‐scale porosities were determined and a unit cell geometry was proposed for modeling. The reduction of the effective pressure due to the gas entrapment was also accounted for. Predictions of the variation of the void content as a function of time, pressure and temperature were compared to experimental data. As a good correlation was found between experiments and predictions, this approach can thus be applied to the consolidation of textile reinforcements in which the tows are locally compressed.
Effect of compatibilizer on the structure‐property relationships of kenaf‐fiber/polypropylene composites
Authors: Feng Daan , Caulfield D. F. , Sanadi A. R.
Published: April 2004

Although lignocellulosic, fiber‐thermoplastics composites have been used for several decades, recent economic and environmental advantages have resulted in significant commercial interest in the use of these fibers for several applications. Kenaf is a fast growing annual growth plant that is harvested for its bast fibers. These fibers have excellent specific properties and have potential to be outstanding reinforcing fillers in plastics. This paper reports the structure‐property relationships of kenaf fiber reinforced polypropylene (PP) and its impact copolymers. The use of maleated polypropylenes (MAPP) is important to improve the compatibility between the fiber and matrix. A significant improvement in impact strengths was observed when the MAPP was used in the composites. Results also indicate that the impact copolymer blends with coupling agent have better high temperature moduli and lower creep compliance than the uncoupled systems. The coupling agent also changes the crystallization and melting behavior of these blends. Because of the better adhesion between the polymer molecules and kenaf fibers, the coupled samples have more restricted molecules than the uncoupled blends. As a result, the crystallization of the coupled high molecular weight blends is slower than the uncoupled blends, resulting in a lower crystallization temperature (Tc) and reduced crystallinity. For the lower molecular weight blends, the coupling agent enhances the crystallization of polymer matrix and results in a higher crystallization temperature and increased crystallinity of the coupled blend. The coupled blends also have more defects in the polymer crystals, and the crystallinity of coupled blends is also lower than the uncoupled blends. This could explain the lower melting temperatures of the coupled samples as compared to uncoupled samples.
Jute felt composite from lignin modified phenolic resin
Authors: Sarkar Sanjay , Adhikari Basudam
Published: April 2004

Raw and dewaxed jute felt composites were prepared with resol and lignin modified phenol formaldehyde resin. Four different types of lignin modified resins were used by replacing phenol with lignin. The lignin modified resins were prepared from purified lignin obtained from paper industry waste black liquor. To investigate bonding between jute and resin, IR spectroscopy of jute felts and composites was carried out. The thermal stability of the composites was assessed by DSC and TGA. It was found that the lignin resin jute composite is thermally more stable than resol composite. XRD of jute felt and composite shows that the crystallinity of the jute fiber increases after composite preparation. The lignin resin composites were tested for water absorption and thickness swelling, and it was found that the results are comparable with those of resol jute composite. Composites prepared from lignin phenol formaldehyde resin with 50% phenol replacement has shown 75% tensile strength retention to that of pure resol jute composite.
Improved model of orthotropic closure approximation for flow induced fiber orientation
Authors: Chung Du Hwan , Kwon Tai Hun
Published: April 2004

We developed improved models (called ORW and ORW3) of existing “orthotropic fitted” closure approximations (ORF or ORL) for use with a wide range of fiber‐fiber interaction coefficients. Closure approximation refers to the approximation of a higher order tensor in terms of a lower order tensor. Principal values of the 4th order tensor are assumed in terms of polynomial expansions of the eigenvalues of the 2nd order tensor. Unknown parameters are determined by a least‐square fitting technique with assumed exact solutions. Flow data for the optimal fitting were designed to cover the entire domain of the orientation triangle as uniformly as possible to eliminate non‐physical oscillation. Shear/biaxial stretching combined flow turns out to play an important role in covering the orientation triangle, thereby increasing the accuracy of fiber orientation prediction. When tested for a variety of flow cases, neither ORW nor ORW3 shows any of the non‐physical oscillatory behaviors that ORF and ORL frequently suffer from.
Role of vacuum pressure and port locations on flow front control for liquid composite molding process
Authors: Hsiao Kuang‐Ting , Gillespie John W. , Advani Suresh G. , Fink Bruce K.
Published: April 2004

In this paper, the influence of air pressure gradients at the flow front, due to presence of two air vents under different vacuum pressures, is investigated for Liquid Composites Molding (LCM) Processes such as Resin Transfer Molding (RTM) and Vacuum Assisted Resin Transfer Molding (VARTM). An analytical mode introduced to predict the pressure distribution. It is suggested that the air press variation along the flow front can be used to control the flow front progress during the injection molding processes. The parametric studies identify a simple relationship that captures the most important process physics, which in prat can be implemented for flow front control.
A process performance index and its application to optimization of the rtm process
Authors: Jiang Shunliang , Zhang Chuck , Wang Ben
Published: April 2004

Resin transfer molding (RTM) is a promising manufacturing process for hig formance composite materials. However, the fact that RTM process design has traditionally been an expensive, time‐consuming trial‐and‐error procedure has p ited its wide application base. This paper proposes a solution to that problem—a simulation‐based optimum process design scheme for RTM. This scheme ei engineers to determine the optimum locations of injection gates and vents so both process efficiency and high part quality can be ensured. Essential to this mum process design scheme is a process performance index, which is defined respect to the major factors influencing RTM process efficiency and part quality This index is then used as the objective function for the RTM process design optimization model. Gate and vent locations are the process design parameters optimized. All data is obtained by running an RTM simulation program, and th netic algorithm (GA) is employed to carry out the optimization procedure for design parameters. It is found that constant pressure optimization will yi process with a short flow path, whereas constant flow optimization will yield process with smooth and vent‐oriented flow pattern. Although there is no dry factor in the objective function, it is interesting to note that both constant pres and constant flow optimization procedures result in process designs with a mil mum probability of dry spot formation. This study finds that, in general, cons flow optimization should be employed if injection pressure is not a major cone otherwise, constant pressure optimization should be used. Two case studies presented to illustrate the efficacy of this approach.
Delamination characteristics of multi‐directional carbon fiber/epoxy composites under high pressure
Authors: Rhee Kyong Yop , Oh Hwan Sup , Jang Seung Ho , Park Soo‐Jin
Published: April 2004

It was shown in a previous study that for unidirectional (0‐deg) graphite/epoxy composites, the fracture toughness under hydrostatic pressure increased 38% as hydrostatic pressure increased from 0.1 MPa to 200 MPa. This work investigates the compressive delamination behavior of multi‐directional graphite/epoxy laminated composites subjected to various hydrostatic pressures. Compressive delamination tests were performed under four hydrostatic pressure levels: 0.1, 100, 200, and 300 MPa Eighty‐eight‐ply dog‐bone type specimens with a single delamination at the center of the specimen were used. The stacking sequence applied was [0°/±45°/90°]lls. The compliance and fracture load were determined from load‐displacement curves as a function of hydrostatic pressure.

The results show that the compliance decreases with increasing pressure while fracture load increases with increasing pressure. The compressive delamination toughness, Gc, was determined from the compliance method as a function of applied hydrostatic pressure. The results also show that Gc is significantly affected by hydrostatic pressure and increases from 2.11 kJ/m2 to 3.04 kJ/m2 (44% increase) as hydrostatic pressure increased from 0.1 MPa to 300 MPa. Visual examination of the fractured surface revealed that the increase of Gc is due to the suppression of micro‐cracks With increasing pressure. It was also found from SEM examination of delaminated surface that the Gc increase is due to more epoxy adhering to the fibers and more plastic deformation of epoxy material as applied hydrostatic pressure increases.
Interfacial adhesion in jute‐polyolefin composites
Authors: Tripathy S. S. , Levita G. , Di Landro L.
Published: April 2004

The interfacial adhesion between four different forms of jute fibers (sliver, bleached, mercerized and untreated) and polyolefinic matrices (LDPE and PP) was studied, as a critical factor affecting the mechanical behavior of these composites. The fiber‐matrix adhesion was estimated by means of the critical fiber length (lc) and the stress transfer ability parameter (τ); such parameters were obtained by Single Fiber Composite (SFC) tests. Tests were carried out to evaluate the mean tensile strength of the fibers, the mean critical fiber lengths and the stress transfer ability parameter for every fiber‐matrix combination, according to Weibull's statistical method. Thermal‐mechanical characterization of the fibers was also carried out to evaluate the resistance to processing conditions. A limited degradation of strength was observed, which, however, does not preclude the use of jute fibers as reinforcing means in polyolefin based composites. It was found that the adhesion was better in PP‐jute composites than in LDPE‐jute composites. In both cases the results showed that the sliver jute and the untreated jute had better adhesion to both matrices than had the bleached and the mercerized fibers. With both matrices the interface adhesion was in the order: mercerized < bleached < untreated = sliver.
Dynamics of binder displacement in liquid molding
Authors: Chen Jinglei , Backes Douglas , Jayaraman K.
Published: April 2004

This paper provides experimental data and an analytical description for mass transfer of soluble thermoplastic binder from a fiber preform to the resin during nonisothermal filling in liquid molding processes. The variation of binder concentration in resin during fill and the viscosity variation must be determined and controlled. This is because of the consequences for wet‐out, preform deformation, development of “fingering” flow patterns and nonuniformities in molded parts. Experimental binder washout curves have been obtained from random continuous glass mat preforms with a range of flow lengths, into a vinyl ester resin. An experimental method developed in this work was then used to estimate from such washout curves the binder concentration profiles within resin at the end of fill for the entire preform. Thus binder concentrations in the resin at the end of fill are seen to vary from 1 to 5 wt%. This range of binder concentrations yields a viscosity increase of more than two‐fold within the mold. A model has been developed and tested for the resin viscosity that takes into account three factors—binder dissolution, temperature variations, and a small amount of cure. This relation has been incorporated into a process model for one‐dimensional flow in a heated mold. Two parameters for the mass transfer coefficient relation were estimated from a run at a reference mold wall temperature. The model then provided good estimates over a range of mold wall temperatures, for binder concentration profiles as well as temperature profiles during filling, that match with experimental data to within 10%. Hence the model describes the interaction between nonisothermal effects and binder dissolution effects well. Calculations with this model thus provide quick estimates of viscosity variation under various process conditions. Design guidelines based on the predicted viscosity variation have also been developed for operating conditions in resin transfer molding.
In‐plane permeability determination for simulation of liquid composite molding of complex shapes
Authors: Rudd C. D. , Long A. C. , McGeehin P. , Smith P.
Published: April 2004

Process simulation forms an important part of the design loop for parts manufactured by liquid composite molding. Critical to this is the determination of accurate permeability data. While constitutive models and test methods for determination of in‐plane permeability of mats and fabrics exist, these do not take account of the effects of changes in fiber architecture during preform manufacture. The deformation behavior of mats and fabrics is reviewed, leading to fiber architecture predictions based upon deformed geometry. Existing models are applied to estimate the distribution of in‐plane permeabilities within the preform based upon the predicted fiber architecture. The predictions are compared with test results for pre‐stretched and pre‐sheared reinforcements, and the method is demonstrated for two prototype automotive parts.
Heat transfer and reaction issues in liquid composite molding
Authors: Tucker Charles L.
Published: April 2004

This paper surveys current issues in the modeling of heat transfer and chemical reaction in resin transfer molding and structural reaction injection molding. The discussion is organized around four steps of modeling: incorporating the physical phenomena into a model, gathering material data, analyzing the model to provide physical understanding, and solving the model for relevant cases. The local volume averaging approach is summarized as a method for deriving appropriate balance equations. The resulting equations are analyzed using dimensional analysis, and analytical solutions are presented for several special cases. These include steady heat transfer for small and large Graetz numbers, and a transient solution for heat transfer during filling at large Graetz numbers. This latter solution explains why preheating the fibers does not heat the resin uniformly. Numerical solution methods are discussed, with emphasis on upwinding techniques for hyperbolic problems. The paper concludes with a summary of research achievements and needs.
Consolidation and cure simulations for laminated composites
Authors: Young Wen‐Bin
Published: April 2004

Fiber reinforced polymer composites have been increasingly used in various structural components. One of the important processes for fabricating high performance laminated composites is autoclave assisted prepreg lay‐up. Since the quality of laminated composites is largely affected by the cure cycle, selection of the cure cycle for each particular application is important and must be optimized. Thus, some fundamental model of the consolidation and cure processes is necessary to properly select the suitable parameters for each application. This study used the viscoelastic solid model for the consolidation of the laminate. In addition, variations of permeability and thermal properties caused by the change of the fiber volume content during the consolidation process were also included. Simulated thickness variations of epoxy continuous carbon fiber prepreg (AS4/3501‐6 from Hercules) laminate under consolidation were compared to the experimental results to test the model. Based on the model analysis, one can predict the pressure, velocity, and laminate thickness during the consolidation process, which can be used to properly select the cure cycle for applications of laminated composites.
A new curvature‐driven delamination test for measuring the mode II toughness of composites
Authors: Matsumoto D. S. , Vallance M. A. , Gifford S. K.
Published: April 2004

The measurement of the delamination toughness of composites requires fracture tests with well‐characterized geometries. Because the delamination toughness is frequently used as a material selection parameter, it is necessary to differentiate between experimental artifacts, data scatter, and changes in the mechanism of delamination. This new Curvature‐Driven Delamination (CDD) test for Mode II provides a direct, steady‐state measurement of the pure Mode II delamination toughness without the compliance calculations inherent in other delamination test protocols. Like the Wedge‐Driven Delamination (WDD) test for Mode I, the CDD Mode II test measures the toughness at controlled crack growth rates. The CDD Mode II test correlates well with the results of the established End‐Notch Flexure (ENF) Mode II test but is not subject to the geometric instabilities of that test. Changes in the delamination mechanism are easily observed by the direct, continuous measurement of the toughness in the CDD Mode II test.
Experimental verification of models for induction heating of continuous‐carbon‐fiber composites
Authors: Fink Bruce K. , McCullough Roy L. , Gillespie John W.
Published: April 2004

Heating of continuous‐carbon‐fiber‐reinforced polymers (CFRPs) by the application of an alternating magnetic field has been shown to be due to dielectric losses in the polymer. Models that predict thermal generation in these composites are input to a finite element heat transfer analysis, providing the predicted transient thermal profile in the plane of the laminate. The validity of the global thermal generation model is established through an experimental test matrix in which various specimen configurations are evaluated and compared with theoretical predictions of transient surface temperatures.
Mold filling analysis in resin transfer molding
Authors: Calhoun Daryl R. , Yalvaç Selim , Wetters Derrick G. , Wu Cheng‐Hsien , Wang T. James , Tsai J. Stephen , Lee L. James
Published: April 2004

This study is a comparison of independently designed mold flow experiments performed at The Dow Chemical Company with simulations from a computer code developed at The Ohio State University. The experiments used in the validation study included isothermal 1‐dimensional flow with line gating and end venting, isothermal 2‐dimensional flow with converging flow and center venting, and two different resin systems. The simulation results were compared with experimental pressure and temperature readings and fill times. It was found that simulated fill times could be predicted within experimental error and pressure distributions could be predicted with the application of a scaling factor.
Sensor system for monitoring impregnation and cure during resin transfer molding
Authors: Schwab Scott D. , Levy Ram L. , Glover Gregg G.
Published: April 2004

In the resin transfer molding (RTM) fabrication of composites, knowledge of the position of a moving resin front during impregnation is important for process optimization. We describe here a simple, inexpensive, multi‐point sensor system based on DC conductometry for determination of resin position in an RTM mold. This Resin Position Sensor (RPS) system consists of a matrix of small sensors embedded in the RTM tool, whose combined output can be used to produce a resin flow pattern at any given time after the start of impregnation. As it cures, the resin resistance increases and the sensor can then function as a cure monitor. A large, 24‐sensor RTM tool was fabricated for demonstration of the RPS. Flow contour maps generated from sensor data during impregnation of both E‐glass and carbon fiber preforms are shown.
Modeling the deformation of thermoformable random fiber reinforcements during preform manufacture
Authors: Long A. C. , Rudd C. D. , Middleton V.
Published: April 2004

Liquid molding processes have been identified by the automotive and aerospace industries as having potential for structural and semistructural applications. Of the several obstacles to their more widespread use, the major drawback is the lack of an automated and reliable technology for producing reinforcement preforms. Current preform technology is usually based on the forming of continuous fiber mats or fabrics between matched molds. This can result in defects within the fiber structure including wrinkling, thinning, and, in extreme cases, tearing. To understand and eliminate these defects, it is necessary to develop a simulation of the preforming process. This paper is aimed at developing a mathematical model of the deformation of thermoformable continuous filament random mat. The analysis presented is based on plasticity theory, suitably modified to describe the behavior of fiber reinforcements. This is demonstrated for the stretch‐forming of reinforcement using arbitrary axisymmetric punch and die profiles. Experimental work is included to demonstrate the effect of varying a range of process parameters, including rate of forming, reinforcement temperature, and stack thickness. The Validity of the model is demonstrated for a number of punch geometries.
Charaterization of UHMWPE fiber/matrix adhesion by dynamic mechanical spectrometry
Authors: Arnold J. J. , Zamora M. P. , Brennan A. B.
Published: April 2004

The tensile and dynamic mechanical properties of polystyrene and a poly(styrene‐co‐buty1 acrylate‐co‐cyclohexy1 methacrylate) statistical terpolymer (terpolymer) reinforced by randomly oriented, discontinuous ultra‐high molecular weight polyethylene (UHMWPE) fibers are presented in terms of the fiber/matrix interfacial properties. Using a thermomechanical block model based on the parallel rule of mixtures, the adhesion characteristics of poly(butyl acrylate) (PBA) and poly(cyclohexyl methacrylate) (PCHM) grafted, plasma treated, and untreated fibers were determined. The model successfully predicts the tan δ response of the composites including peak height variations and the development of additional loss dispersions associated with the interphase. Moreover, the model yields a fiber reinforcement efficiency factor, K, which gives a quantitative measure of adhesion. The contact angle of PBA and PCHM grafted high density polyethylene (HDPE) films are also included and are compared to the contact angle of plasma treated fibers. The results indicate that PBA and PCHM grafts enhance adhesion through polymer graft/matrix interactions, not simply by improved wetting.
Time‐implicit fixed and deforming grid solutions for compression mold filling
Authors: Chen Y. F. , Voller V. R. , Stelson K. A.
Published: April 2004

A general governing equation for tracking the filling free surface during compression molding is derived. From this equation, with appropriate choice of parameters, a time‐implicit fixed grid solution and a time‐implicit deforming grid solution are obtained. Numerical results of several test problems reveal that both solutions reach the same level of accuracy. The fixed grid scheme, however, is more robust and can solve problem with complex geometrical features.
The modulus of shear‐induced fibers from a thermotropic liquid crystalline polymer in a thermoplastic matrix
Authors: Yi Xiao Su , Shi Fang , Michaeli Walter
Published: April 2004

A morphological study was performed to determine the volume fraction and the aspect ratio of shear‐induced fibers from a thermotropic liquid crystalline polymer (LCP) in a polycarbonate (PC) matrix. A set of micromechanical models was then applied to estimate the elastic modulus of LCP fibers (Eƒ) in a LCP(20 wt%)/PC blend. The dependence of the composite modulus (Et) of the blend on sample dimensions was predicted. The effects of different injection molding conditions on fiber aspect ratio, Et and Eƒ, were examined.
Effects of thermal history on mechanical behavior of PEEK and its short‐fiber composites
Authors: Sarasua J. R. , Remiro P. M. , Pouyet J.
Published: April 2004

The effect of crystallinity differences induced by mold wall temperature and annealing on mechanical behavior is evaluated for poly(etheretherketone) (PEEK) resin and its composites. The systems investigated were neat PEEK, glass fiber (GF) reinforced PEEK, and carbon fiber (CF) reinforced PEEK. Both composite systems were reinforced with 10, 20, and 30 wt% fiber. The degree of crystallinity (Xc) of PEEK was found to increase by processing at higher mold temperatures, by annealing, and by fiber length reductions, which appears to indicate the ability of short fibers to nucleate the crystallization of PEEK under favorable thermal conditions. Improvements in Young's modulus and strength together with ductility reductions are generally obtained as crystallinity increases in both neat PEEK and its composites. The contribution of crystallinity to mechanical behavior is significant only for neat PEEK and PEEK reinforced by 10% fiber. SEM micrographs reveal that this is due to a change in failure mode. When PEEK is reinforced by carbon fibers or by 20–30% glass fibers, a macroscopic brittle mode of failure is observed irrespective of matrix crystallinity, and mechanical behavior is principally determined by the nature and content of the reinforcing fibers.
Analysis of pultrusion processing of composites of unsaturated polyester resin with glass fibers
Authors: Moschiar S. M. , Reboredo M. M. , Kenny J. M. , Vázquez A.
Published: April 2004

An analysis of the principal processing variables of pultrusion of a thermosetting matrix composite is presented. A fundamental study of the changes of temperature, degree of reaction, and resin viscosity is performed through the application of transfer phenomena principles. Moreover, the development of pressure in the die and the required pulling force are modeled and compared with experimental results reported previously by other authors on the pultrusion of unsaturated polyester matrix‐glass fiber composites. The modeling approach discussed here integrates several sub‐models, reported previously, to obtain a complete description of the basic aspects of the pultrusion process. The application of the mathematical model allows a better understanding of the relationship between processing conditions and material behavior leading to the determination of the processing window for a given system.
Recyclability of a glass fiber poly(butylene terephthalate) composite
Authors: Chu J. , Sullivan J. L.
Published: April 2004

The recyclability of a fiber‐reinforced poly(butylene terephthalate) (PET) composite has been studied. After treatment with a suitable silane, processed regrind composites are successfully recycled, with mechanical properties as good as a comparable, commercial composite. The three processing techniques investigated are injection molding, extrusion compression molding and compression molding. As expected, processing technique and processing parameters are important in determining the mechanical properties of the molded regrind. Our results show that injection‐ and extrusion‐compression‐molded regrind composites have good fiber bundle dispersion and fiber alignment, resulting in tensile properties better than the compression‐molded samples. On the other hand, compression‐molded samples, which show random fiber orientation and low fiber bundle dispersion, have lower tensile properties, but better impact strength than injection‐ and extrusioncompression‐molded composites.
Mechanical and physical properties of isothermally aged carbon fiber‐epoxy composites
Authors: Chifu A. F. , Iroh J. O.
Published: April 2004

Isothermal aging of continuous carbon fiber‐epoxy resin composites containing epoxy resin derived from diglycidyl ether of bisphenol‐A (DGEBA) and methylene dianiline (MDA) and 64 vol% of carbon fibers with orientation angles of 0°, 45°, 90° and crossply fibers was performed in vacuum, air and nitrogen atmosphere. The impact strength of the 45° ply composites increased from 149 kJ/m2 to 15.5 × 102 kJ/m2 after isothermal aging in vacuum at 200°C for 13 h. The interlaminar shear strength (ILSS) of the 90° ply composites increased from 3 to 4 MPa after isothermal aging at 184°C for 336 h in nitrogen atmosphere. The flexural strength of the 90° ply composites, however, remained unchanged (∼80 MPa) after isothermal aging in nitrogen at 184°C for 336 h. The impact strength of the 90 degree ply composites decreased by 20% (∼15 kJ/m2 to 12 kJ/m2) and 80% (∼15 kJ/m2 to 3 kJ/m2) after isothermal aging in nitrogen atmosphere at 184°C for 336 h and in air at 200°C for 336 h, respectively.
Tough low profile additives in sheet molding compound
Authors: Chan‐Park Mary B. , McGarry Frederick J.
Published: April 2004

Thermosetting polyester in a sheet molding compound (SMC) shrinks by 7 to 10% and causes fiber show‐through and poor surface quality. Adding certain thermoplastics results in zero shrinkage and smooth surfaces; these are called low‐profile additives (LPA). Poly(vinyl acetate) (PVAc), a highly effective LPA, decreases the fracture energy from 66.3 to 35.1 J/m2 when present as 14 wt% of the matrix, even though the PVAc is tough. It produces a nodular three dimensional network; the crosslinked polyester nodules are interconnected by weak polyester bridges and the PVAc forms a thin coating on each nodule. The macroscopic crosslinking shrinkage is offset by void formation in the PVAc phase. Crack follows the void structure and cleaves the bridges between the nodules. Low matrix fracture toughness leads to high microcracking and early gross failure of the SMC. This paper presents alternative low profile additives that give excellent low profile effect with improved matrix fracture energy and SMC strength. Commercially available styrene‐butadiene block copolymers were studied. These are less polar and form discrete cavitated domains of a few 100 μm in the solid polyester matrix. With this morphology, good low profile and toughening usually are contradictory, since the former requires small LPA particles for smooth surfaces and the latter requires large particles for crack bridging by the rubber. However, a good compromise was found in Epoxidized Kraton D1300X (a 50% diblock and 50% triblock copolymer of styrene and butadiene) with the compatibilizer Ricon 131MA17 (a maleic anhydride‐polybutadiene adduct). This produces a low profile effect equivalent to PVAc, but with a higher matrix fracture energy of 70.7 J/m2 and higher matrix modulus. With the epoxidized rubber, the flexural strength of the SMC increases by 13% over that with PVAc, with no sacrifice of the modulus or strain‐to‐failure.