bluuebunny/crossref_metadata_2025 huggingface dataset:
Short term flexural creep behavior of wood‐fiber/polypropylene composites
Authors: Park Byung‐Dae , Balatinecz John J.
Published: April 2004

Short term flexural creep tests were conducted to investigate the creep behavior of wood‐fiber polypropylene composites. Three experimental parameters were selected: the addition of a wetting agent, temperature, and wood‐fiber concentration. All creep curves are presented in terms of relative creep as a percentage of instantaneous (initial) strain. The creep power law model was used to accurately fit the creep data. The addition of a wetting agent greatly reduced the creep at high stress, but had little effect at a lower stress level. The extent of relative creep increased with increasing temperature. It was found that the slope of the power law model was directly proportional to the temperature. The addition of wood‐fibers into pure polymer greatly improved the creep resistance of the matrix polymer. The relative creep of the composites decreased with an increase in wood‐fiber concentration. However, the composite showed relatively large creep compared with that of solid wood. It was found that both the time exponent and slope of the power law model were inversely related to wood‐fiber concentration. The flexural modulus of the composites also had an inverse relationship with the time exponent.
The development of glass fiber reinforced polystyrene for pultrusion. I: Process feasibility, dynamic mechanical properties, and postformability
Authors: Chen Chin‐Hsing , Wang Wen‐Si
Published: April 2004

A feasibility study on the pultrusion of a glass fiber reinforced polystyrene (PS) has been conducted using a proprietary method. The styrene prepolymer synthesized in this study was prepared from blends of styrene monomer and benzoyl peroxide (BPO). The process feasibility, dynamic mechanical properties, and postformability of the glass fiber reinforced PS by pultrusion have been investigated. By means of gel permeation chromatography, 1H nuclear magnetic resonance (1H‐NMR), and a Brookfield viscometer, the molecular weight, conversion, and viscosity of the styrene prepolymer were obtained. From the investigations of the long pot life of styrene prepolymer, the high reactivity of styrene prepolymer, and excellent fiber wet‐out, it was found that the PS resin showed excellent process feasibility for pultrusion. The dynamic storage modulus (E') of pultruded glass fiber reinforced PS composites increased with increasing die temperature, filler content, postcuring and glass fiber content, and with decreasing pulling rate. The composite can be postformed by thermoforming under pressure, and mechanical properties of postformed composites can be improved.
The development of glass fiber reinforced polystyrene for pultrusion. II: Effect of processing parameters for optimizing the process
Authors: Chen Chin‐Hsing , Wang Wen‐Si
Published: April 2004

This paper presents a novel process developed to manufacture polystyrene (PS) pultruded composites. The effects of the processing parameters on the mechanical properties (tensile strength, flexural strength, flexural modulus, etc.) of the glass fiber reinforced PS composites by pultrusion have been studied. The processing parameters investigated include die temperature, pulling rate (in‐line speed), postcure temperature and time, filler type and content, and glass fiber content. The optimum die temperature was determined from DSC diagrams, molecular weight, and mechanical properties tests. It was found that the mechanical properties increased with increasing die temperature and glass fiber content, and with decreasing pulling rate. The optimum die temperature, pulling rate, and glass fiber content were determined to be 160–200°C, 20–60 cm/min and 50–60 vol%, respectively. The mechanical properties reached a maximum value at 10 phr kaolin, and then decreased. However, the properties decreased with increasing tale content. The mechanical properties increase at a suitable postcure temperature and time. Furthermore, the properties that decreased as a result of composite degradation after long postcure time are discussed.
Influence of interfacial interactions on the properties of PVC/cellulosic fiber composites
Authors: Matuana Laurent M. , Woodhams Raymond T. , Balatinecz John J. , Park Chul B.
Published: April 2004

The surface properties at the interface between thermoplastic and cellulosic fibers strongly influence the mechanical properties of plastic/cellulosic fiber composites. This paper examines the role of surface acid‐base properties of plasticized PVC and cellulosic fibers on the mechanical properties of the composites. The acid‐base surface characteristics of cellulosic fibers were modified by treating the fibers with γ‐aminopropyltriethoxysilane (A‐1100), dichlorodiethylsilane, phthalic anhydride, and maleated polypropylene. The empirical acid (KA) and base (KD) characteristics (i.e., electron donor/acceptor abilities) of untreated and treated fibers, as well as plasticized PVC, were determined using inverse gas chromatography (IGC) technique. These parameters were used to yield information on the acid‐base pair interactions that were correlated with the tensile and notched Izod impact properties of the composites. Acid‐base pair interactions have been found to be a valuable parameter in the design of surface modification strategies intended to optimize the tensile strength of the composites. By tailoring the acid‐base characteristics of cellulosic fibers and plasticized PVC, a composite with equal tensile strength and greater modulus than unfilled PVC was developed. However, the acid‐base factors did not correlate with tensile modulus, the elongation at break, and the notched Izod impact property of PVC/newsprint fiber composites. Aminosilane has been observed to be a suitable adhesion promoter for PVC/wood composites improving significantly the tensile strength of the composites. Other treatments (dichlorodiethylsilane, phtalic anhydride, and maleated polypropylene) were found to be ineffective, giving similar strength compared to the composites with untreated cellulosic fibers. FTIR spectroscopy results suggested that aminosilane was effective because treated cellulosic fibers can react with PVC to form chemical bonds. The resulting bond between PVC and cellulosic fibers accounts for the effectiveness of aminosilane, when compared with other coupling agents.
Effect of post‐curing on the mechanical properties of carbonized phenolic resins
Authors: Ko Tse‐Hao , Ma Tsu‐Sheng
Published: April 2004

After curing, phenol‐formaldehyde resins were post‐cured at 160°C, 230°C, and 300°C in air for several hours, and then those post‐cured samples were carbonized at 1000°C. The effect of post‐curing on the physical properties and microstructure of the carbonized phenolic resin is reported in this article. The purpose of post‐curing was to improve the mechanical properties of the carbonized resins. The post‐curing process promoted the crosslinking reaction and the evolution of gases. The cured resin post‐cured at a higher post‐curing temperature (300°C) had a significantly higher weight loss, greater linear shrinkage and lower density than others samples. During carbonization the post‐curing process not only decreased the weight loss but also limited the shrinkage. Post‐curing also promoted the formation of carbon basal planes and the chemical densification in structures of the final carbonized resins. The increase in post‐curing temperature and time had the effect of reducing the linear shrinkage of the resin during carbonization. The TGA thermal analysis showed that the post‐cured resins improved the total weight loss more than 15 wt% over the unpost‐cured resin. The carbonized resins developed from the post‐cured resins had a greater flexural modulus by about 10–50% and improved the linear shrinkage by about 10% over that developed from unpost‐cured resin.
Analysis of an injection/compression liquid composite molding process
Authors: Han Kerang , Ni Jun , Toth James , Lee L. James , Greene Joseph P.
Published: April 2004

The injection/compression liquid composite molding (LCM) process is simulated by using the control/volume finite element method (CV/FEM). The flow in the runner and the fiber‐free areas is simplified by using an equivalent permeability approach. Several molding experiments were conducted using a tub‐shaped mold and the structural reaction injection molding (SRIM) process for a poly(urethane/isocyanurate) matrix and a glass fiber preform. Good agreement is found between the experimental results and the simulation.
A generalized self‐consistent mori‐tanaka scheme for prediction of the effective elastic moduli of hybrid multiphase particulate composites
Authors: Dai L. H. , Huang Z. P. , Wang R.
Published: April 2004

A generalized self‐consistent Mori‐Tanaka method (GSCMTM) is developed in this paper. The method starts with the formulation of the problem of heterogeneous elasticity proposed by Dederichs and Zeller and incorporates the strain equivalence condition of Christensen's generalized self‐consistent method (GSCM) and Hill's interfacial operator theory into the evaluation of the strain concentration tensors of constituents. For a two‐phase composite with spherical inclusions, the effective moduli predicted by GSCMTM coincide with those predicted by the Mori‐Tanaka method (MTM). By a two‐step homogenization technique, GSCMTM was successfully extended to multiphase composites. The effective moduli predicted by GSCMTM for multiphase hybrid particulate composites agree well with the existing theoretical and experimental results and can be expressed in a simple explicit form.
Creep and relaxation behavior of woven glass/epoxy substrates for multilayer circuit board applications
Authors: Shrotriya P. , Sottos N. R.
Published: April 2004

The creep behavior of a common woven glass/epoxy composite substrate for multilayer circuit board applications was characterized using dynamic mechanical analysis (DMA). The creep compliance was measured in both the warp and fill directions of the composite over a temperature range of 30°C to 155°C. The creep compliance of the neat FR‐4 epoxy matrix was also characterized for comparison with the composite response. Master creep curves were obtained for the neat resin and the composite in the warp and fill directions assuming thermorheologically simple behavior and applying the time‐temperature superposition principle. The creep data was fit to a Prony series and then converted to relaxation data in the Laplace domain. Micromechanical models were developed to predict the relaxation behavior of the woven glass/epoxy composite from the elastic properties and the geometry of the glass fabric and relaxation behavior of the neat resin. Model predictions were compared with experimental data.
Anisotropic modeling of isothermal squeezing flow of Glass‐Mat reinforced thermoplastics (GMT)
Authors: Dweib M. A. , Brádaigh C. M. Ó
Published: April 2004

Lubricated isothermal compression molding of Glass‐Mat Thermoplastic (GMT) was carried out using a circular mold on a 100 kN test machine to characterize the rheological parameters for squeezing flows of the material. Flow was found to be anisotropic with the main flow direction perpendicular to the main fiber direction. In‐plane flow of circular specimens was found to follow an elliptical shape, which allows a relationship to be derived between extensional strain rates in the two main in‐plane directions. A transversely isotropic incompressible Newtonian fluid model was successfully applied to interpret the squeezing data parallel and perpendicular to the main flow direction. Longitudinal and transverse extensional viscosities were calculated for two squeezing temperatures, 180°C and 200°C. The results were compared to the standard isotropic power law interpretation, showing the largest anisotropic viscosity to be 20% higher than the isotropic viscosity at low closing speeds and 9.5% higher at fast closing speeds. A very significant difference in the viscosities was found between the two different temperatures as the viscosity at 200°C dropped to about 65% of its value at 180°C. In this work, original material sheets were also confirmed to display anisotropic mechanical properties. The final squeezed specimens were found to have different fiber volume fractions in the same specimen.
Impact behavior of carbon fiber/polyethylene fiber hybrid composite: The effect of surface treatment of polyethylene fiber
Authors: Park Rohchoon , Jang Jyongsik
Published: April 2004

Hybrid composites were prepared by adding one or two plies of polyethylene (PE) fabric to the bottom side of four‐ply carbon fiber/vinylester composites. The effect of the surface treatment of PE fiber on the impact properties of carbon fiber/PE fiber hybrid composites was investigated using oxygen plasma, γ‐MPS, and γ‐MPS‐modified polybutadiene (PB/γ‐MPS) as surface modifiers. Carbon fiber/vinylester composite exhibited brittle failure with cross‐shaped crack at the back side. The addition of PE fabric on the bottom side resulted in a change of the impact behavior of hybrid composites. After hybridization, the absorption of much impact energy was attributed to a considerable degree of plastic deformation in PE plies and the delamination at the interface between carbon and PE layer. However, the surface treatment of PE fiber reduced the impact energy of composites with restriction of deformation at the interface between the carbon and the PE layer. Moreover, the addition of a treated PE layer decreased the degree of deformation with a dagger‐shaped deformation zone at the back side. The extent of the deformation area had a significant effect on the impact energy of the hybrid composites.
Effect of carbon fabric type on the mechanical performance of 2D carbon/carbon composites
Authors: Ko Tse‐Hao , Kuo Wen‐Shyong
Published: April 2004

A stabilized PAN fabric was carbonized and graphitized from 800°C to 2500°C. Two‐dimensional (2D) carbon/carbon composites were made using the stabilized PAN fabric, carbonized fabrics, and a resol‐type phenol‐formaldehyde resin. These composites were heat‐treated from 600°C to 2500°C. The influence of different heat‐treated fabrics and heat treatment on the fracture and flexural strength of these composites was also studied. The composite reinforced with higher heat‐treated fabrics showed a lower weight loss than that with lower heat‐treated fabrics. When the composites were graphitized at 2500°C, the loss was 49.7 wt% for the composite made with stabilized PAN fabric and 26 wt% for that with carbonized fabric at 2500°C. Those composites also have a higher density than composites produced by other methods. Composites made with stabilized PAN fabric exhibited a strong bonding in the fiber/matrix during pyrolysis. This composite showed catastrophic fracture and a smooth fracture surface with no fiber pullout. Composites made with higher carbonized fabrics exhibited a weak interface bonding. These composites showed a pseudo‐plastic fracture pattern with fiber pullout during pyrolysis. Composites made with carbonized fabrics at 2000°C and 2500°C showed the highest flexural strength at the prolysis temperature of 1000°C. Composites made with carbonized fabric at 1300°C showed the highest flexural strength above 1500°C to 2500°C. The composite made with stabilized PAN fabric exhibited the lowest flexural strength during pyrolysis.
Dynamic mechanical properties of spherical inclusions in polymer composite: A self‐consistent approach considering morphology
Authors: Shaterzadeh M. , Gauthier C. , Gerard J. F. , Mai C. , Perez J.
Published: April 2004

In this work, the dynamic mechanical behavior of epoxy/A‐glass bead composites is investigated considering the influence of the volume fraction of the beads and their surface treatments. The main differences between the different samples are observed in the rubbery modulus plateau. The “Self‐Consistent Scheme” is used to calculate the effective shear modulus of the composite with spherical inclusions, i.e., a macroscopically isotropic polymer medium containing spheres. The 3‐phase model first introduced by Christensen and Lo accurately predicts results for the composite with treated glass beads (sizing agent), but fails for the other one (untreated surface). For the latter composite, other related models (4‐phase models) are also applied without satisfactory results. Then, the 3‐phase model is applied in successive steps to account for the specific distribution of glass.
Moisture absorption effect on adhesive filled bonded joints
Authors: Ouddane M. , Boukhili R.
Published: April 2004

The effect of filler type and content on the performance and durability of adhesive bonded joints upon exposure to damp heat (water immersion) has been investigated using concurrently step lap shear and thermo mechanical analysis (TMA) experiments. A TMA based approach is developed in order to predict the strength of the bonded constructions. Two types of fillers were used in order to achieve the objectives: glass beads (GB) and alumina ceramic powder (ACP). It is shown that ACP filled adhesives have higher strength retention than GB filled ones. It is also demonstrated that valuable information can be extracted from TMA measurements. Generally, the increase of the coefficient of thermal expansion (CTE) of the bonded joints is found to be in agreement with the decrease of the step lap joint strengths after exposure. The increase of the CTE of the bonded joints resulting from exposure to hot water seems to increase the stresses, which in turn affect the overall strength. Similarly, bulk adhesive results show that GB filled systems are more susceptible to water than ACP filled ones, which confirms the decrease in strength of GB filled bonded constructions.
Crystallinity of isothermally and nonisothermally crystallized poly(ether ether ketone) composites
Authors: Chen Ming , Chung Chia‐Ting
Published: April 2004

PEEK/carbon fiber composites were prepared by a modified diaphragm forming machine under vacuum. The study of the degree of crystallinity versus the differential scanning calorimetry (DSC) heating rate indicated that 50°C/min was an optimal heating rate to suppress the reorganization of the specimens crystallized between 315°C and 255°C and to avoid superheating the specimens. A high volume of fibers constrained the spherulitic growth by an impingement mechanism, which depressed the crystallization rate and reduced the crystallinity. Thus the crystallization was still in process even after 240 min annealing at 300°C. The effect of the cooling rate on the degree of crystallinity was simulated and investigated in DSC at a heating rate of 50°C/min. The results indicated that the cooling rates ranging from 1°C/min to 100°C/min could be divided into five regions that were associated with a high volume of fiber and the crystallization regime. A Time‐Temperature‐Transformation diagram superposed on the Continuous‐Cooling‐Transformation curves allows us to predict the amount of crystallization in different regimes. The data points for the DSC method deviated from the prediction at the cooling rates above 60°C/min because of the recrystallization during DSC heating scans.
Toughening of carbon fiber/thermoset composite by the morphology spectrum concept
Authors: Kim Yu‐Seung , Kim Sung‐Chul
Published: April 2004

Morphology spectrum toughening, a novel technique for toughening brittle carbon fiber/thermoset composites, was applied to a polyetherimide‐modified carbon fiber/dicyanate composite. Composites were prepared by inserting a polyetherimide film between the prepregs of carbon fabric impregnated by dicyanate alone, and by controlling both the relative rates of dissolution of the polyetherimide and the polymerization of the dicyanate by adding zinc stearate catalyst. A composite with 13 wt% polyetherimide afforded a mode I interlaminar fracture toughness of 1.4 kJ/m2, almost 1.8 times higher than that of a control composite containing same composition of polyetherimide. Two effects were observed. First, a thermoplastic continuous morphology formed in the center interply zone, where the concentration of polyetherimide was high, provided good fracture toughness. Second, a thermosetting continuous morphology formed in the fiber‐rich zone, where the concentration of polyetherimide was low, maintained good interfacial shear strength between the fiber and the matrix.
Investigation of the role of transverse flow in co‐injection resin transfer molding
Authors: Gillio Emanuele F. , Advani Suresh G. , Gillespie John W. , Fink Bruce K.
Published: April 2004

A co‐injection resin transfer molding (CIRTM) process has been developed at the University of Delaware's Center for Composite Materials in collaboration with the U.S. Army Research Laboratory. It enables two or more resins to be simultaneously injected into a mold filled with a stationary fiber preform. This process allows for the manufacturing of co‐cured multi‐layer, multi‐resin structures in a single processing step. A separation layer is used to provide resin compatibility during cure and to control resin mixing. Scaling issues relating the role of transverse permeability in resin mixing are investigated. This study presents two different approaches taken to understand the causes of transverse flow and to quantify the amount of transverse flow that occurs during processing. The first approach, a one‐dimensional model, explains the important parameters that govern resin flow in CIRTM. The second approach is based on an existing finite element code that is modified to allow for the injection of multiple resins. The total amount of transverse flow was quantified using the finite element code. This research shows that the CIRTM process requires a totally impermeable separation layer if CIRTM is used to manufacture large parts and/or if the resins injected have significantly different viscosities.
An a priori grid permutation for isothermal flow models
Authors: Freese Colin E. , Walsh Shawn M.
Published: April 2004

Mesh permutations are used to enhance the computational efficiency of an implicit finite element based scheme for modeling isothermal incompressible viscous flow through a permeable medium. A new software implementation of the implicit algorithm permits a realization of these potential savings and is discussed in some detail. The efficiency of the modeling application is shown to be particularly sensitive to the ordering of the grid nodes. An a priori arrangement of nodes approximating the order of their activation (fill) during the actual simulation is indicated. A new ordering procedure is proposed to achieve this task. The algorithm utilizes both geometric relationships and modeling parameters and demonstrates predictive capabilities analogous to the actual flow simulation while requiring a fraction of the computational resources. Examples are used to verify and quantify the efficiency projections and to investigate the apparent contradictory objectives of the proposed grid permutation with those of the more familiar profile or bandwith minimization procedures.
Product design with glass fiber reinforced polymer blends, with potential applications in recycling
Authors: Xanthos M. , Narh K. A.
Published: April 2004

This paper addresses the issue of compositional variation in multiphase, multi‐component polymer mixtures equivalent to those found in commingled waste streams, such as those obtained from reclamation/recycling operations of post‐consumer containers. By using virgin resins, the effects of variations in the composition of matrices containing high density polyethylene (HDPE) as the major phase on the properties of composites containing varying amounts of glass fiber and different adhesion promoters are studied. The results obtained on injection molded thin‐section parts indicate that it is possible, through the addition of glass fibers and in the presence of suitable adhesion promoters, to obtain enhanced and reproducible properties with relatively little dependence on matrix composition. Preliminary structural and flow analyses were performed with commercial software on different types of plastic parts that could be eventually molded from actual mixed waste plastics suitably modified through glass reinforcement. Experimentally generated rheological and mechanical property data on HDPE based blends containing 20 wt% glass fibers and different adhesion promoters were used for the simulation. Issues concerned with injection molding and product performance of glass‐fiber reinforced blends are discussed.
Effects of rate and temperature on fracture behavior of TPX (poly‐4‐methyl‐1‐pentene) polymer
Authors: Ye Lin , Yuan Chao‐Ting , Mai Yiu‐Wing
Published: April 2004

The fracture behavior of TPX (poly‐4‐methyl‐1‐pentene) polymer was studied using compact tension (CT) and single‐edge‐notch bending (SENB) specimens. Effects of crosshead rate and environmental temperature (−40°C to 160°C) on fracture behavior were investigated. Fractographic analyses were conducted after fracture tests using scanning electron microscopy (SEM). The results showed that the fracture behavior of the TPX polymer was highly dependent on crosshead rate and temperature. Unstable‐stable transition of crack growth and stiky‐slip behavior were observed for both low and high crosshead rates when the environmental temperature was increased.
Injectin molding of short fiber reinforced thermoplastics in a center‐gated mold
Authors: Larsen Å.
Published: April 2004

We have studied injection molding of a rectangular box using short fiber reinforced polypropylene. The fiber orientation distribution and the local stiffness properties in radial and transverse directions have been measured in the bottom plane. The deduced orientation tensors are compared with predictions of a commercial computer code. Discrepancies are related to approximations made in the calculations and effects not accounted for by the present modeling approach. In the calculations the fiber interaction coefficient was varied seeking to fit experiments. We comment on the out‐of‐plane components of the orientation tensor, the relative thickness of skin and core layers, and the radial dependence of the fiber orientation in each layer. Values of the components of the 4th‐order orientation tensor calculated from the measured orientation distribution are used to compare different closure approximations referred in the literature. Anisotropy in the stiffness properties, calculated form the measured fiber orientation, agree well with measurements.
Structure and mechanical properties of fast cooled and annealed poly(phenylene sulfide)/Vectra A blends
Authors: Ruiz De Gauna B. E. , Gaztelumendi M. , Nazábal J.
Published: April 2004

Poly(phenylene sulfide) (PPS)/Vectra A blends were directly injection molded and obtained throughout the composition range both as molded, low crystallinity, and annealed highly crystalline materials. The blends were immiscible, but, contrary to an earlier work on PPS/Vectra A blends, they showed a clear fibrous morphology that was a consequence of the higher viscosity of the matrix compared with that of the Vectra A at the shear strain rate used. The mechanical properties of the annealed blends showed that when highly crystalline materials are sought, annealing post‐cold molding is a valid alternative to molding at high mold temperatures. The fracture properties of the as‐molded blends, such as ductility and tensile strength, were higher than in annealed blends, as a consequence of the higher deformability of the less crystalline structure. The presence of the LCP in the as‐molded low‐crystallinity PPS blends counteracts their intrinsic lower stiffness by means of a faster stiffness increase when Vectra A was added, compared with that which took place in annealed blends. These facts rendered the as‐molded PPS/Vectra A blends alternative materials to the usual highly crystalline ones.
Processing conditions and compatibilizing effects on reinforcement of polypropylene‐liquid crystalline polymer blends
Authors: Farasoglou P. , Kontou E. , Spathis G. , Gomez Ribelles J. L. , Gallego Ferrer G.
Published: April 2004

The effect of the processing conditions in respect to the presence of maleic anhydride‐grafted polypropylene on the thermomechanical properties of two series of polyropylene‐liquid crystalline polymer blends has been studied. Two types of Liquid Crystalline Polymers (LCPs) which were copolyesters, namely Vectra A and Vectra B have been used. A systematic study of processing conditions such as die temperature, speed of mixing, and speed of elongation, as well as the presence of compatibilizer, has been made. The blends were tested in terms of tensile experiments and dynamic mechanical analysis. The experimental data were connected with interesting remarks about the morphology of the materials, and this analysis has been supported with Scanning Electron Microscopy (SEM) micrographs.
Pulling tension monitoring during the melt impregnation of glass roving
Authors: Bates P. J. , Charrier J. M.
Published: April 2004

The force required to pull a 2400 tex glass roving through a melt impregnation compounding process was studied. Pulling force was continuously measured by suspending the double belt puller in a sling held stationary by a force transducer. Process variables such as roving pulling speed, number of cylindrical pins, pin diameter, and melt temperature were studied using polymide 66 and polypropylene polymers. The results suggest that the tension build‐up in the roving is caused by a combination of two effects: viscous shear stresses in a thin polymer‐rich layer between the roving and the pin, as well as frictional forces caused by roving contact with the pin. A simple mathematical model is developed and used to adequately describe the experimental results.
A machine system for the rapid production of composite structures
Authors: Brown Jessica H. , Colton Jonathan S.
Published: April 2004

A rapid manufacturing process for thermosetting materials was developed to produce composite structures in a manner similar to rapid prototyping. The machine system builds the part layer by layer with continuous curing and consolidation, making traditional curing methods unnecessary. Each part layer, which has been prestaged to provide a desired degree of cure, moves under a heat gun and a roller for curing and consolidation. The heat gun initiates the cure in the part layer, partially curing it and making it tacky enough for the next layer to stick to it when it goes through the consolidation process. The cure continues to advance as each layer is placed. Testing was performed by fabricating three‐layer parts and performing tests on single strips of towpreg to determine how temperature and time affect the degree of cure. The material was IM7 carbon fiber/977‐3 epoxy towpreg, prestaged in a tunnel oven to an approximate 30% degree of cure. Hot air temperatures of 150 – 380°C (302 – 716°F), roller forces of 236 – 472 N (53 – 106 Ibf), table speeds of 13 – 38 mm/sec (0.5 – 1.5 in/sec), and times of exposure to hot air of 5, 10, and 20 seconds were used. The results showed that the machine system can continuously cure and consolidate parts. The cure was advanced to any level up to 100% degree of cure with an air temperature of 380°C. Parts were produced with layers well stuck together. Within the limitations of the experiments, temperature was determined to be the most significant factor affecting degree of cure. With the correct processing conditions, the machine system has the capability to produce well‐consolidated, high quality parts without using traditional curing methods. The design of the machine system allows for the addition of components for the fabrication of arbitrarily shaped parts and for different curing methods.
Experimental analysis and numerical modeling of flow channel effects in resin transfer molding
Authors: Bickerton S. , Advani S. G. , Mohan R. V. , Shires D. R.
Published: April 2004

Composite manufacturing by Liquid Composite Molding (LCM) processes such as Resin Transfer Molding involve the impregnation of a net‐shape fiber reinforcing perform a mold cavity by a polymeric resin. The success of the process and part manufacture depends on the complete impregnation of the dry fiber preform. Race tracking refers to the common phenomenon occurring near corners, bends, airgaps and other geometrical complexities involving sharp curvatures within a mold cavity creating fiber free and highly porous regions. These regions provide paths of low flow resistance to the resin filling the mold, and may drastically affect flow front advancement, injection and mold pressures. While racetracking has traditionally been viewed as an unwanted effect, pre‐determined racetracking due to flow channels can be used to enhance the mold filling process. Advantages obtained through controlled use of racetracking include, reduction of injection and mold pressures required to fill a mold, for constant flow rate injection, or shorter mold filling times for constant pressure injection. Flow channels may also allow for the resin to be channeled to areas of the mold that need to be filled early in the process. Modeling and integration of the flow channel effects in the available LCM flow simulations based on Darcian flow equations require the determination of equivalent permeabilities to define the resistance to flow through well‐defined flow channels. These permeabilities can then be applied directly within existing LCM flow simulations. The present work experimentally investigates mold filling during resin transfer molding in the presence of flow channels within a simple mold configuration. Experimental flow frot and pressure data measurements are employed to experimentally validate and demonstrate the positive effect of flow channels. Transient flow progression and pressure data obtained during the experiments are employed to investigate and validate the analytical predictions of equivalent permeability for a rectangular flow channel. Both experimental data and numerical simulations are presented to validate and characterize the equivalent permeability model and approach, while demonstrating the role of flow channels in reducing the injection and mold pressures and redistributing the flow.
Effect of stacking sequence on the compressive performance of impacted aramid fiber/glass fiber hybrid composite
Authors: Park Rohchoon , Jang Jyongsik
Published: April 2004

Aramid fiber/glass fiber hybrid composites were prepared to examine the compressive performance of impacted composites. The effect of stacking sequence and surface treatment on compression after impact (CAI) performance of three‐layer hybrid composites was investigated with respect to delamination area. As the impact velocity increased, the laminates exhibited a significant reduction of compressive strength owing to larger delamination area within laminate. The surface treatment aramid fiber reduced the delamination area and enhanced the resistance to buckling. The strength reduction of laminate AAA was considerable because of wide delaminated region, whereas the residual strength of laminate GGG was not affected by impact energy because the laminate absorbed most of impact energy through formation of fiber cracks rather than delamination. Considering stacking sequence, the laminate GAG and GAA exhibited an energy threshold due to insensitivity to impact damage. As a result, the residual performance of composite was primarily dominated by delamination extent rather than fiber cracks.
Modeling compression molding of all‐thermoplastic honeycomb core sandwich components. Part A: Model development
Authors: åkermo Malin , Tomas åström B.
Published: April 2004

The compression molding process is studied with the aim of modeling the instantaneous degree of face‐core bonding in all‐thermoplastic sandwich components during molding. The theory of bonding is briefly discussed and it is concluded that for most thermoplastic materials, processing is performed at temperatures where full bond strength is seemingly immmediately established at positions in full face core contact. A two‐dimensional model is developed to predict increase in contact area due to flow of melted core material during molding. Further, heat transfer during processing is modeled in order to determine the extent of melted core material. The two models are coupled into one process model and a numerical example is presented illustrating the predicted behavior of polypropylene‐based sandwich components in compresion molding. The process model suggests that the face‐core bond strength may be significantly increased through flow of the melted core wall.
Compression after impact (CAI) strength of concrete cylinders reinforced by non‐adhesive filament wound composites
Authors: Tai Nyan‐Hwa , Liu Hsien‐Kuang , Chen Zhi‐Cheng
Published: April 2004

Concrete cylinders reinforced by filament wound composites were fabricated, and the compressive strength of the composite/concrete cylinders was tested after low‐energy impact. In this study, a glass fiber woven cloth wrapping method and a filament winding technique were adopted to wrap the concrete cylinder. In order to investigate the influence of composite/concrete interfacial bonding on the compression after impact (CAI) strength, aluminum foil was introduced into the composite/concrete interface; thus, the compressive behavior of the composite/concrete system with or without inserting the aluminum foil was compared. The effects of aluminum foil in the curing process were also revealed. Based upon the results of this study, the placement of aluminum foil can significantly enhance the compressive strength of the composite/concrete cylinder. The CAI strength depicts that the winding angle used in the filament winding process can significantly influence the reinforcing effects. Among the tested cylinders, the FWIC (defined in the text) [902/±60/902] cylinder shows the highest CAI strength—129.4 MPa—which is 4.5 times higher than the impacted concrete cylinder and 4.1 times higher than the pure concrete cylinder. Fracture mode was also investigated on the cylinder reinforced by the composites wound with different winding angles. The placement of aluminum foil reduces shear stress transfer across the composite/concrete interface, which affects not only the impact response but also the compressive strength.
Carbon fiber reinforced phenolic Resin/Silica ceramer composites—processing, mechanical and thermal properties
Authors: Lin Jia‐Min , Ma Chen‐Chi M. , Tai Nyan‐Hwa , Chang Wen‐Chi , Tsai Chuan‐Chung
Published: April 2004

Phenolic/silica ceramers were prepared by the sol‐gel method. Carbon fiber reinforced phenolic/silica ceramer composites with high thermal resistance were fabricated. Tetraethyl orthosilicate (TEOS) was used as a monomer for sol‐gel system. Different ratios of the sol‐gel solutoins and phenolic resins were adopted and the resulting ceramers were used as matrices for carbon fiber reinforced composites. The mechanical and thermal properties of the fabricated composites were studied. The results show that the incorporation of inorganic ingredients into the phenolic resins will increase the thermal resistance of the fabricated composites but not affect the flexural strength of the carbon fiber reinforced phenolic/silica ceramer composites up to 60 wt%. The morphologies of the ceramer matrices were examined by SEM. SiO2 particles from at the gaps between fibers for higher inorganic contents.
Impact behavior of a short glass fiber reinforced thermoplastic polyurethane
Authors: Jancar J.
Published: April 2004

The temperature dependence of critical strain energy release rate (Gc′) and standardized Charpy notched impact strength (CNIS) were measured for a thermoplastic polyurethane (TPUR) reinforced with 30 wt% of short glass fibers (SGF) over a temperature interval ranging from −150°C 23°C (RT) at two strain rates, 70 and 150 s−1, respectively. Fractographic observation of fracture planes was used to qualitatively assess the fracture modes and mechanisms. Adhesion between the reinforcement and the matrix was excellent and the integrity of the fiber‐matrix interfacial contact was relatively insensitive to exposure to hydrolysis during the immersion in boiling water for 100 hours. At temperatures above −30°C, there was a large extent of plastic deformation in the vicinity of crack planes while at temperatures below −50°C, the extent of plastic deformation was substantially reduced. This resulted in a change in the major energy dissipation mechanism and led to a decrease of both CNIS and Gc′ values for SGF/TPUR composites. It was suggested that the plastic deformation of TPUR matrix in the immediate vicinity of glass fibers was the primary source of energy dissipation at temperatures above −30°C, while the friction and fiber pull‐out was the main dissipative process below −50°C. Over the whole temperature interval investigated, greater Gc′ values were obtained at higher strain rate of 150 s−1, without any significant change in the fractographic patterns observed on the fracture planes. The CNIS/Gc′ ratio, used to assess suitability of CNIS for comparison of materials, changed with temperature substantially suggesting that the functional dependences of CNIS and Gc′ on temperature differ substantially. Hence, CNIS data do not provide a reliable base for material selection and for design purposes in this case.
Interfacial stress transfer in nylon‐6/E‐Glass microcomposites: Effect of temperature and strain rate
Authors: Pegoretti Alessandro , Fambri Luca , Migliaresi Claudio
Published: April 2004

In this study, the interfacial properties between E‐glass fibers with different commercial sizings have been investigated on model composites with a nylon‐6 matrix. In particular, the fiber critical length was measured by means of the single‐fiber fragmentation test over a wide range of temperatures (from 25 to 175°C) and strain rates (from 0.0008 to 4 min−1). The general trend observed is that the fiber critical aspect ratio increases as the temperature increases and it decreases as strain rate is increased. The fiber critical aspect ratio for unsized fibers resulted to be reasonably well linearly related to the square root of the fiber to matrix modulus ratio. This results is in accordance with the Cox's shear‐lag theoretical model and the Termonia's numerical simulations. Sized fibers display an higher deviation from the theoretical prevision probably because of the presence of interphases whose properties are different from the bulk matrix. As a consequence, the interfacial shear strength values resulted to be dependent on the fiber sizing. In particular, the fibers coated with an epoxy sizing showed a superior thermal stability of the fiber matrix‐interface with respect to the unsized or nylon compatible sized fibers.
Interface modification and characterization in three‐component polymer blends
Authors: Fisher I. , Zoldan J. , Siegmann A. , Narkis M.
Published: April 2004

The effect of interface characteristics on the properties of three‐component polymer blends comprising PP/EVOH/mica and PP/EVOH/glass beads (GB) was investigated (polypropylene‐PP, ethylene‐vinylalcohol‐EVOH). The systems selected are based on the binary PP/EVOH immiscible blend representing a semi‐crystalline apolar polymer (PP) and a semi‐crystalline highly polar copolymer (EVOH), where PP serves as the matrix. A series of the binary and three‐component blends with varying compositions was chosen to study the effect of the molding procedure, i.e. compression versus injection molding. The structures observed by SEM analysis consisted of the filler particles engulfed by the EVOH phase, with some of the minor EVOH component dispersed within the PP matrix. The effects of silane treatment (GB/EVOH interface) and compatibilization, using a maleated‐PP compatibilizer (PP/EVOH interface), were studied in relation to the generated structured and properties. The compatibilizer was added in a unique procedure by which the encapsulated GB/EVOH structures were preserved. The characterization methods used included morphology by Scanning Electron Microscopy, thermal properties and crystallization behavior by Differential Scanning Calorimetry, mechanical properties by tensile testing, and dynamic characteristics by Dynamic Mechanical Thermal Analysis. The work has shown that structure‐performance relationships in the three‐component blends can be varied and controlled.
Mechanical properties of glass fiber/organic fiber mixed–mat reinforced thermoplastic composites
Authors: Kitano T. , Haghani E. , Tanegashima T. , Saha P.
Published: April 2004

The purpose of this study is to investigate the influence of different types of fibers on the mechanical properties of hybrid composite materials. Long and short glass fibers (GF) and different types of organic fibers, viz. aramid fiber, DuPont Kevlar‐49 (KF), liquid crystalline polymer (LCP), and vinylon (VF) in hybrid composites, were used to reinforced the high density polyethylene (HDPE) matrix. The long fiber hybrid composites were prepared in a “fiber separating and flying machine,” while the short fiber hybrid composites were prepared in an “elastic extruder.” The total amount of fibers used in both long and short fiber hybrid composites was fixed at 20 vol%. The influence of fiber content, length, and mixing ratio on mechanical properties, such as tensile, bending, Izod and high rate impact strength, as well as viscoelastic propertics in the solid state, was studied. Fracture surfaces of the materials were also examined using a scanning electron microscopy.
Swirl mat– and long discontinuous fiber mat–reinforced polypropylene composites—status and future trends
Authors: Karger‐Kocsis J.
Published: April 2004

Polypropylene (PP) composites with glass and natural fiber mat reinforcement (GMT‐PP and NMT‐PP, respectively) are widely used in different applications, competing with metallic sheets and thermoset polymer composites. Their production occurs via melt impregnation, slurry deposition and various textile architecturing processes that lead to either consolidated or non‐consolidated preforms. These preforms are then converted into final parts by hot pressing. The “traditional” GMT‐PP composites are nowadays faced with a great challenge because of the introduction of long fiber reinforced thermoplastic (LFT) composites produced on‐ or off‐line. This paper gives a brief survey on the manufacturing, processing, properties and application of GMT and GMT‐like systems and it concludes by describing some of the future trends, especially in the fields of material and process developments.
Stamping of continuous fiber thermoplastic composites
Authors: Chen Julie , Sherwood James A. , Buso Patricia , Chow Samuel , Lussier Darin
Published: April 2004

Despite demonstrated success in low volume aerospace and defense applications, structural composites remain at the periphery of high volume industries such as construction, automotive, and consumer goods because of long cycle times. Stamping provides a means of making composite sheet products at rates ten to a hundred times faster than any existing continuous fiber processes. However, to make composites stamping a viable process, one must understand how the combination of fabric architecture, tool design, and process conditions interact to produce a part free of wrinkling and tearing. In this paper, the effect of temperature, stamping rate, and boundary constraints on the material deformation is presented. The focus of this study is a co‐mingled glass/polypropylene fabric, in the form of a layer of unidirectional yarns held together by stitches. The results show that temperature variations have the greatest effect on deformation. In addition, a finite element model of parallel strips with linear constraints was shown to successfully simulate the sliding deformation or draw‐in of the stitched unidirectional material.