bluuebunny/crossref_metadata_2025 huggingface dataset:
Structural properties and mechanical behavior of injection molded composites of polypropylene and sisal fiber
Authors: Xie X. L. , Li R. K. Y. , Tjong S. C. , Mai Y.‐W.
Published: April 2004

Composites based on isotactic polypropylene (PP) and sisal fiber (SF) were prepared by melt mixing and injection molding. The melt mixing characteristics, thermal properties, morphology, crystalline structure, and mechanical behavior of the PP/SF composites were systematically investigated. The results show that the PP/SF composites can be melt mixed and injection molded under similar conditions as the PP homo‐polymer. For the composites with low sisal fiber content, the fibers act as sites for the nucleation of PP spherulites, and accelerate the crystallization rate and enhance the degree of crystallinity of PP. On the other hand, when the sisal fiber content is high, the fibers hinder the molecular chain motion of PP, and retard the crystallization. The inclusion of sisal fiber induces the formation of β‐form PP crystals in the PP/SF composites and produces little change in the inter‐planar spacing corresponding to the various diffraction peaks of PP. The apparent crystal size as indicated by the several diffraction peaks such as L(110)α, L(040)α, L(130)α and L(300)β of the α and β‐form crystals tend to increase in the PP/SF composites considerably. These results lead to the increase in the melting temperature of PP. Moreover, the stiffness of the PP/SF composites is improved by the addition of sisal fibers, but their tensile strength decreases because of the poor interfacial bonding. The PP/SF composites are toughened by the sisal fibers due to the formation of β‐form PP crystals and the pull‐out of sisal fibers from the PP matrix, both factors retard crack growth.
In situ monitoring of residual strain development during composite cure
Authors: Crasto Allan S. , Kim Ran Y. , Russell John D.
Published: April 2004

Internal (residual) stresses build up in a thermosetting composite as the matrix shrinks during cure, and again as the composite is cooled to ambient from its elevated processing temperature. These stresses can be significant enough to distort the dimensions and shape of a cured part as well as initiate damage in off‐axis plies, either during fabrication or under the application of relatively low mechanical loads. The magnitude of these stresses depends on a number of factors including constituent anisotropy, volume fraction and thermal expansion, ply orientation, process cycle, and matrix cure chemistry. In this study, embedded strain gauges were employed to follow, in situ, the buildup of residual strains in carbon fiber‐reinforced laminates during cure. The data were compared to those from volumetric dilatometer studies to ascertain the fraction of resin shrinkage that contributed to residual stress buildup during cure. Based on earlier studies with single‐fiber model composites, the process cycle in each case was then varied to determine if the cycles optimized to minimize residual stresses for isolated fibers in an infinite matrix were applicable to the reduction of residual stresses in conventional multifiber composites. The results of these studies are reported here.
The effect of interface characteristics on the static and dynamic mechanical properties of three‐component polymer alloys
Authors: Fisher I. , Siegmann A. , Narkis M.
Published: April 2004

The effect of interfacial characteristics on the structure‐property relationships of ternary polymer alloys and blends comprising polypropylene (PP), ethylene‐vinyl alcohol copolymer (EVOH) and glass beads (GB) or fibers (GF) was investigated. The systems studied were based on a binary PP/EVOH immiscible blend, representing a blend of a semi‐crystalline apolar polymer with a semi‐crystalline highly polar copolymer. The ternary systems studied consisted of filler particles encapsulated by EVOH, with some of the minor EVOH component separately dispersed within the PP matrix. Modification of the interfacial properties was done using silane coupling agents for the EVOH/glass interface and compatibilization using a maleic anhydride grafted PP (MA‐g‐PP) for the PP/EVOH interface.

Both glass fillers increased the dynamic modulus and decreased the damping of the neat polymers and of their binary blends, especially in the rubbery region. GF has a more profound effect on both the modulus and the damping. Glass surface treatments and compatibilization have only a marginal effect on the dynamic mechanical behavior of the ternary blends. Yet, compatibilization shifted the polymers' TgS to higher temperatures.

Both glass fillers increased the elastic modulus of the binary blends, where GF performed better than GB as a reinforcing agent. GF slightly increased the strength of the binary blends while, GB reduced it. Both fillers reduced the ductility of the binary blends. The blends' mechanical properties were related to the morphology and their components' crystallinity. The compatibilizer increases both stiffness and strength and reduces deformability.
Monitoring the reaction progress of a high‐performance phenylethynyl‐terminated poly(etherlmide). Part II: Advancement of glass transition temperature
Authors: Bullions Todd A. , Stoykovich M. P. , McGrath J. E. , Loos A. C.
Published: April 2004

The cure schedule for carbon fiber‐reinforced, phenylethynyl‐terminated Ultem™ (GE Plastics) composites was studied in an attempt to optimize the resultant glass transition temperature, Tg. Reaction progress and possible matrix degradation were monitored via the Tg. On the basis of previous research, matrix degradation induced Tg reduction was expected for increases in cure time or temperature beyond approximately 70 minutes at 350°C. Using the central composite design (CCD) of experiment technique, composite panels, neat resin, and polymer powder‐coated tow (towpreg) were cured following various cure schedules to allow for the measurement of the glass transition temperatures resulting fronm cure time and temperature variations. The towpreg and neat resin specimens were cured in a differential scanning calorimeter. The glass transition temperatures of all specimens were measured via differential scanning calorimetry; the composite glass transition temperatures were also measured with dynamic mechanical thermal analysis. The composite panels and towpreg specimens showed similar trends in Tg response to cure schedule variations. Composite and towpreg glass transition temperatures increased to a plateau with increasing cure time and temperature, whereas, the neat resin showed an optimal Tg followed by Tg reduction with increasing cure time and temperature. The optimal neat resin Tg occurred within a cure time and temperature significantly below that required to maximize the composite and towpreg glass transition temperatures.
Dynamic viscoelasticity of hybrid kevlar and glass fiber reinforced LLDPE in the molten state
Authors: Hashmi S. A. R. , Kitano Takeshi , Chand Navin
Published: April 2004

Kevlar and glass fibers were used to reinforce linear low density polyethylene (LLDPE), and composite sheets of 0.8, 1.5 and 2.5 mm thicknesses were obtained by using a compression molding technique. Dynamic viscoelastic properties of non‐hybrid and hybrid composites of various compositions at 200°C are evaluated. Storage modulus (G′) and loss modulus (G″) increase with angular frequency (ω) and reinforcement. Replacement of glass fiber by Kevlar at constant loading of fibers in LLDPE increases the value of G′, G″ and η′. The fractured surface of composite shows the gradient orientation of fibers particularly in 2.5 mm thick sheet. Top and bottom layers show relatively two‐dimensional orientation as compared to the middle layer, which shows random orientation. The orientation of fibers decreases G′ and η′ of Kevlar fiber and hybrid fiber hybrid fiber reinforced LLDPE composites. The effect of change in distance between parallel plate of rheometer (change in strain amplitude) on dynamic rheological properties is studied and reported here.
The role of a third component on the conductivity behavior of ternary epoxy/Ag conductive composites
Authors: Jia W. , Tchoudakov R. , Joseph R. , Narkis M. , Siegmann A.
Published: April 2004

Conductive adhesives, based on highly filled silver particles dispersed in a liquid epoxy resin, with an aliphatic amine [diethyltriamine (DETA)] as a curing agent, were investigated. A third component was added to the epoxy/Ag system to obtain composites of better conductivity, or similar conductivity but at lower silver contents, to modify the conductive adhesive properties, and also to reduce cost. Epoxy/Ag/carbon black (CB), epoxy/Ag/carbon fibrils (CF), epoxy/Ag/SiO2 and epoxy/Ag/dispersant composites were thus studied. The effect of high curing temperature on the uniformity and resulting conductivity level was also studied. The studied systems, excluding the epoxy/Ag/CB composite, exhibited enhanced conductivities. The microstructure of most of the systems was studied by scanning electron microscopy (SEM). The micrographs produced have served to establish structure‐property relations for better understanding of the observed phenomena.
Non‐Isotropic structured fibrous media: The permeability of arrays of fiber bundles of elliptical cross section
Authors: Papathanasiou T. D. , Gravel E. M. , Barwick S. C. , Dendy E. D.
Published: April 2004

A computational analysis of viscous flow across hexagonal arrays of fiber bundles of elliptical cross section, each consisting of up to 350 individual filaments, is carried out using the Boundary Element Method. Such arrays are non‐isotropic dualporosity systems, characterized by the aspect ratio (λ) of the fiber bundles, their inter‐ (ϕi) and intra‐tow (ϕt) porosities as well as by the number (Nf) of filaments within each bundle. The results, in terms of the hyraulic permeability (K) of these arrays, are compared to earlier analytical models and a good agreement is found. A dimensionless correlation, earlier proposed for arrays of circular cross section, is used to reduce the computed permeabilities for bundles of aspect ratio λ = 2 and λ = 3 on a single master curve. This correlation offers a simple model for the calculation of the permeability of such dual porosity systems form knowledge of ϕi, ϕt, λ and Nf. By considering bulk flow along the two principal directions of the fiber bundle, we also compare the two principal permeabilities of such arrays.
Thermokinetic effect of the aging of epoxy matrix prepregs for high performance composites
Authors: Frigione M. , Kenny J. M.
Published: April 2004

The reactivity and processability of prepregs for high performance composites have been investigated as a function of time and storing conditions. The study has been focused on the stability of epoxy matrix carbon fiber prepregs, affected by exposure to controlled environmental conditions before their use in composite manufacturing. Effects of the aging on glass transition temperature, reactivity and processability have been investigated by calorimetry. Dynamic, isothermal and cure simulating tests have been performed to this aim. Results on toughened TGDDMDDS epoxy matrix prepregs are reported. A theoretical kinetic model proposed for the unaged system has been adapted for aged prepregs, by properly evaluating the variations of kinetic parameters with the aging time.
Using a localized fluorescent dye to probe the glass/resin interphase
Authors: Lenhart Joseph L. , Van Zanten John H. , Dunkers Joy P. , Parnas Richard S.
Published: April 2004

A novel technique has been developed to study the buried polymer/substrate interfacial regions by localizing a fluorescent probe on the substrate surface. Epoxy functional multi‐layers of silane coupling agents were deposited on glass and doped with small amounts of a fluorescently labeled silane‐coupling agent (FLSCA). When the dye‐doped silane layers were immersed in an epoxy/amine cured resin, a blue shift in the emission maximum was measured after resin cure. Silane layers of varying thickness were tested. Thicker layers showed smaller fluorescence shifts during cure, suggesting incomplete resin penetration into these layers. The fluorescence sensitivity to the interfacial reaction was verified with external reflection Fourier Transform Infrared Spectroscopy (FTIR) of the silane layers immersed only in the amine hardener.
Mechanical properties of glass fiber composites with an epoxy resin modified by a liquid crystalline epoxy
Authors: Punchaipetch Prakaipetch , D'Souza Nandika Anne , Brostow Witold , Smith James T.
Published: April 2004

The effect of liquid crystalline networks on epoxy + glass fiber composites is investigated. The matrix obtained from in‐situ curing of liquid crystalline (LC) diglycidyl ether of 4,4‐dihydroxybiphenol (DGE‐DHBP) with diglycidyl ether of bisphenol F (DGEBP‐F) by anhydride curing agent was used as the matrix for polymer composites. Impact, tensile, and flexural testing results are compared between the unmodified and modified systems. The interlaminar fracture toughness of commposites in the shear mode was determined by end notch flexure (ENF) tests. Scanning electron microscopy is used to study the fracture surfaces to understand the mechanism of fracture and interphase formation between the fiber and the matrix.
New composites based on short melamine fiber reinforced epdm rubber
Authors: Rajeev R. S. , Bhowmick Anil K. , De S. K. , Kao G. J. P. , Bandyopadhyay S.
Published: April 2004

Melamine fibre is a new category of advanced synthetic fiber having superior heat and flame resistance with decomposition temperature above 350°C. It suitability as a reinforcing fiber for ethylene propylene diene terpolymer, abbreviated as EPDM rubber, where ‘M’ stands for polymethylene chain, was investigated. It has been observed that tensile strength and stress at 100% strain of EPDM‐melamine fiber composites increase with the addition of a three‐component dry bonding system, comprising hexamethylene tetramine (hexa), resorcinol, and hydrate silica, abbreviated HRH system. Moreover, the fiber‐filled composites anisotropy in stress‐strain properties due to preferential of the short fibers along the milling direction (longitudinal), which is substantiated by the results of swelling and fractography studies. Aging causes an increase in the modulus, tensile strength and hardness of the composites. The fractographs show an increase in interfacial adhesion between the fibers and the matrix during aging, which is further confirmed by the reduction in tan δ peak height of the aged composites during dynamic mechanical studies. Atomic Force Microscopy (AFM) studies reveal the formation of an interphase with the addition of bonding agents and a better fiber‐matrix adhesion due to aging. AFM images also confirm the role of dry bonding systems in improving the fiber‐matrix adhesion of the aged vulcanizates. The composite modulus has been theoretically calculated using the well‐known Halpin‐Tsai equation. It is found that in the transverse direction, observed modulus values are greater than the calculated values, while in the longitudinal direction, the experimental modulus values are found to be lower than the calculated values for both unaged and aged composites owing to some degree of anisotropy in fiber orientation.
Compatibilization of poly(ethylene terephthalat)/liquid crystal polymer blends by means of bisphenol a polycarboate
Authors: García M. , Eguiazábal J. I. , Nazábal J.
Published: April 2004

A compatibilization method that consists of the addition of minor amounts of a commercial thermoplastic, which interacts or reacts with both the matrix and the dispersed liquid crystalline polymer (LCP) of thermoplastic/LCP blends, has been tested in the case of poly(ethylene terephthalate)/Vectra A950 (PET/VA) blends by means of the addition of bisphenol A polycarbonate (PC). The smaller particle size, rougher surface of the fibers and higher ductility of the PET/VA blends of a 30% of the PET substituted by PC clearly showed the suitability of PC as a compatibilizer. The moduli of elasticity of the compatibilized and uncompatibilized blends were similar. This was due to the less‐developed fibrillation of the compatibilized blends, a consequences of their smaller particle size and decreased matrix viscosity. These changes counteracted the effects of improved interfacial adhesion. The improved adhesion led to higher ductility and tensile and impact strengths in most of the compatibilized blends.
Real‐Time damage detection in thermoplastic‐based composite materials with embedded multi‐mode optical fiber sensors
Authors: Kuang K. S. C. , Cantwell W. J.
Published: April 2004

In this paper we describe the use of an inexpensive standard communication‐grade optical fiber for the purpose of detecting damage in glass fiber reinforced thermoplastic composite materials and hybrid fiber metal laminates based on the same composite constituent. These multi‐mode, step‐index optical fibers were embedded at different locations within the composite structure to assess their ability for structural health monitoring. In this study, the specimens were loaded under a three‐point bend test configuration, Results from the investigation have shown that these optical fibers are capable of detecting the peak failure load in the host material when embedded at locations where structural failure initiates at peak load. The output from the optical fibers was shown to be sensitive to the applied loading conditions suggesting that they can also be used to monitor structural loading. Optical micrographs of selected specimens were obtained by sectioning the specimens at the fracture location to provide confirmation of the optical fiber results.
The preparation of phenolic resin/montmorillonite nanocomposites by suspension condensation polymerization and their morphology
Authors: Wu Zenggang , Zhou Chixing , Qi Rongrong
Published: April 2004

Phenolic resin/clay nanocomposites were prepared using a suspension condensation polymerization method that was suitable to both novolac and resole. Natural montmorillonite and two kinds of organic modified montmorillonite were adopted to investigate the effect of modification on the final morphology of the nanocomposites. X‐ray diffraction (XRD) measurements and Transmission Electron Microscope (TEM) observations showed that clay platelets were easier to be exfoliated or intercalated in novolac than in resole because novolac usually has a linear structure. The modifier with a phenyl ring was more compatible with novolac (or resole) than the aliphatic type modifier. The influence of curing on the morphology was studied as well. An exfoliation‐adsorption and in situ condensation mechanism was proposed on the formation of the nanocomposites.
Development and characterization of an all‐olefin thermoplastic sandwich composite system
Authors: Kumar Ganesan , Ramani Karthik , Xu Chongchen
Published: April 2004

In this investigation an all‐olefin thermoplastic sandwich system was developed and characterized. Commingled glass fiber polypropylene (PP) composite was used as skin and HDPE (PE) foam with closed cells as core. Infra‐red heating was used for melting the surfaces of the substrates for surface fusion bonding with a cold press. Two tie layer films, viz. ethylene‐propylene copolymer (EPC) and HDPE/elastomer blend, were used as hot melt adhesives for bonding the substrates. Single lap shear joints were prepared from PP composite and PE foam adherends with a bonding area of 25.4 mm × 25.4 mm to determine the interface strength. EPC tie layer provided higher bond strength (27.4 kg/cm2) to the all‐olefin sandwich system than HDPE/elastomer blend based one (19.7 kg/cm2). For EPC tie layer based sandwiches, a mixed mode a failure was observed in the failed lap shear samples; about 40% is cohesive failure through tie layer, and the rest of failure was adhesive either at PP composite or PE surfaces. Environmental scanning electron micrographs (ESEM) reveal that in the process of surface fusion bonding, PE foam cells in the vicinity of 0.80 mm interphase area were coalesced with high temperature and pressure. No macro level penetration of tie layer melt front into foam cells was observed. As the surface morphology of foam was altered on account of IR surface heating and the PP composite bonding side had a resin‐rich layer, the bonding situation was closer to that between two polymer film surface.
Polyethylene‐Palygorskite nanocomposite prepared via in situ coordinated polymerization
Authors: Rong Junfeng , Sheng Miao , Li Hangquan , Ruckenstein Eli
Published: April 2004

A polyethylene/palygorskite nano‐composite (IPC composite) was prepared via an in‐situ coordinated polymerization method, using TiCl4 supported on palygorskite fibers as catalyst and alkyl aluminum as co‐catalyst. These composites were compared with those prepared by melt blending (MBC composites). It was found that in the IPC composites, nano‐size fibers of palygorskite were uniformly dispersed in the polyethylene matrix. In contrast, in the MBC composites, the palygorskite was dispersed as large clusters of fibers. Regarding the mechanical properties of the IPCs, the tensile modulus increased and the elongation at break decreased with increasing fiber content, while the tensile strength passed through a maximum. The tensile strength and elongation at break were much smaller for the MBC composites. The final degree of crystallinity of the IPC composites decreased with increasing palygorskite content. Regarding the kinetics of crystallization, the ratio between the degree of crystallinity at a given time and the final one was a universal function of time. It was found that large amouns of gel were present in the IPC composites and much smaller amountes in the MBC composites.
Enhancement of resin transfer molding using articulated tooling
Authors: Choi Jun H. , Dharan C. K. H.
Published: April 2004

Mold articulation is introduced in this concept for resin transfer molding (RTM) to increase mold fill times and potentially allow for the use of high viscosity, hot melt resin systems, or thermoplastics. Following a brief review of conventional RTM and a discussion of the limitations on the factors that control fluid flow through porous media, the articulated concept is described. This is followed by an explanation of the sequence of motion of an articulated segmented mold necessary for consolidation, void removal and accelerated fluid flow through a fibrous preform. An analysis of the process using a fiber preform with orthotropic permeability is outlined from which mold fill time is obtained. This is compared with conventional RTM mold fill times using typical resin properties and fiber volume fractions. For the conservative assumptions used, an improvement by a factor of ten in mold fill time is achieved using the articulated process relative to conventional RTM.
Optimizing injection gate location and cycle time for the in‐mold coating (IMC) process
Authors: Carbera‐Rios Mauricio , Zuyev Konstantin S. , Chen Xu , Castro Jose M. , Straus Elliott J.
Published: April 2004

The standard practice when compression molding Sheet Molding Compound (SMC) exterior automotive body panels is to in‐mold coat (IMC) the parts. Consequently, IMC needs to be considered an integral part when improving the process. Selecting the proper IMC injection gate location to obtain a defect‐free coated part and properly setting the IMC processing conditions to reduce its cycle time are both key decisions for the IMC process. In the present work, an optimization method that involves metamodeling through either linear regression or artificial neural networks is explored with two purposes: first, to select the injection gate location(s) with the objective of minimizing the potential for surface defects in the coating; and second, to set the mold wall temperature and the initiator concentration to minimize the cure time for a given minimum required flow time.
Optimal curing for thermoset matrix composites: Thermochemical and consolidation considerations
Authors: Li Min , Tucker Charles L.
Published: April 2004

A design sensitivity method is used to find optimal autoclave temperature and pressure histories for curing of thermoset‐matrix composite laminates. The method uses a finite element simulation of the heat transfer, curing reaction, and consolidation in the laminate. Analytical sensitivities, based on the direct differentiation method, are used within the finite element simulation to find the design sensitivities, i.e., the derivatives of the objectives function and the constraints with respect to the design variables. Standard gradient‐based optimization techniques are then used to systematically improve the design, until an optimal process design is reached. In this study the objective is to minimize the total time of the cure cycle, while the constraints include a maximum temperature in the laminate (to avoid thermal degradation) and a maximum deviation of the final fiber volume fraction from its target value (to achieve proper consolidation). The simulations of curing process are performed for EPON 862/W epoxy under a conventional cure cycle, for both thin and thick parts. Time‐optimal cure cycles are found using the optimization program. Simulations of fast‐curing cycles are also examined. The optimal cycles are similar in form to conventional cure cycles, but give substantially shorter cure times. The entire scheme works automatically and efficiently, simultaneously adjusting multiple design variables at each iteration.
Numerical computation of the fiber preform permeability tensor by the homogenization method
Authors: Nedanov Pavel B. , Advani Suresh G.
Published: April 2004

This paper uses the homogenization method to formulate governing equations and boundary conditions to predict the permeability of anisotropic fibrous porous media. An approach is also put forth for addressing dual porosity media with this method. It is applicable to a wide range of porous materials, which may be considered with approximately periodic structure. The permeability components are calculated by solving a boundary value problem in a periodic cell. The application of the method is demonstrated on a periodic cell modeling the geometry of woven fiber performs used in composites manufacturing. The resulting equations are solved using CFD package FIDAP. The influence of dual porosity and nesting of adjacent fabric layers on the macro permeability was investigated and the results were compared with experiments.
Comparative study of the effects of different fibers on the processing and properties of ternary composites based on PP‐EPDM blends
Authors: López‐Manchado Miguel A. , Biagitti Jerico , Kenny José M.
Published: April 2004

The effects of the incorporation of different kinds of fibers on the physical and mechanical properties of thermoplastics elastomers based on blends of isotactic polypropylene (iPP) and ethylene‐propylene diene rubber (EPDM) are described. For this purpose, three different compositions of PP‐EPDM blends reinforced with fibers are studied and reported here. In particular, the flow behavior, mechanical properties (tensile, flexural and impact resistance) and morphology are examined. Rheological measurements confirm the viscosity increase of thermoplastics elastomers with the incorporation of the fibers. This increment is more evident in the presence of aramid fibers. In addition, the results obtained by dynamic‐mechanical analysis and mechanical properties show that the fibers act as an effective reinforcing agent of PP‐EPDM blends. In fact, a significant increase of the modulus and strength is obtained in presence of all fibers, this effect being more noticeable at higher elastomer percentages in the thermoplastic. The morphology of the ternary composites is also analyzed by scanning electron microscopy (SEM). A good interfacial adhesion between fibers and matrix is observed, but also in this case, aramid fibers are the most effective ones.
Influences of liquid elastomer additive on the behavior of short glass fiber reinforced epoxy
Authors: Arikan Aslihan , Kaynak Dr. Cevdet , Tincer Teoman
Published: April 2004

In this study, improvements in mechanical and thermal behavior of short glass fiber (GF) reinforced diglycidyl ether of bisphenol‐A (DGEBA) based epoxy with hydroxyl terminated polybutadiene (HTPB) modification have been studied. A silane coupling agent (SCA) with a rubber reactive group was also used to improve the interfacial adhesion between glass fibers and an epoxy matrix. 10, 20, and 30 wt% GF reinforced composite specimens were prepared with and without silane coupling agent treatment of fibers and also HTPB modification of epoxy mixture. In the ruber modified specimens, hardener and HTPB were premixed and left at room temperature for 1 hr before epoxy addition. In order to observe the effects of short glass fiber reinforcement of epoxy matrix, silane treatment of fiber surfaces, and also rubber modification of epoxy on the mechanical behavior of specimens, tension and impact tests were performed. The fracture surfaces and thermal behavior of all specimens were examined by scanning electron microscope (SEM), and dynamic mechanical analysis (DMA), respectively. It can be concluded that increasing the short GF content increased the tensile and impact strengths of the specimens. Moreover, the surface treatment of GFs with SCA and HTPB modification of epoxy improved the mechanical properties because of the strong interaction between fibers, epoxy, and rubber. SEM studies showed that use of SCA improved interfacial bonding between the glass fibers and the epoxy matrix. Moreover, it was found that HTPB domains having relatively round shapes formed in the matrix. These rubber domains led to improved strength and toughness, due mainly to the “rubber toughening” effect in the brittle epoxy matrix.
Lignin‐polypropylene composites. Part 1: Composites from unmodified lignin and polypropylene
Authors: Toriz G. , Denes F. , Young R. A.
Published: April 2004

Lignin polypropylene composites were prepared in the range of 10–60% by weight lignin content. Blending of lignin with polypropylene resulted in materials with reduced tensile and flexural strength and a dramatic decrease in unnotched Izod impact strength compared to the properties of virgin polypropylene, although moduli (Young's and flexural) were improved. Traditional surface‐treated fillers such as mica and talc performed better than lignin, but when lignin and inorganic fillers were mixed, the strength properties were improved with respect to lignin alone, perhaps because of a better lignin‐filler‐particle interaction and distribution. This could be an alternate approach for obtaining improved strength composites containing large quantities of unmodified kraft lignin. Incorporation of maleic anhydride grafted polypropylene (MAPP) as a coupling agent also improved strength properties, although at high lignin contents (e.g. 60%) there was considerable variability in the tensile strength.
A combinatorial approach for automotive friction materials: Combined effects of ingredients on friction performance
Authors: Lu Yafei
Published: April 2004

The combined effects of ingredient A and C in A + B + C systems where A and C are Al2O3, graphite, MoS2, steel wool and Twaron (aramid pulp), and B is a binder (benzoxazine) on friction performance were studied. Ray design with Golden Section was used for the formulated A + B + C ternary composites. Two combined factors, morphological combinations including fiber/fiber, fiber/filler and filler/filler and combinations by means of material nature including abrasive/abrasive, abrasive/lubricant and lubricant/lubricant, and their composition dependence were considered. Synergetic effects, defined as a minimum wear in wear‐composition relationships, were found in morphological combinations of fiber/filler (steel wool/Al2O3/B and Twaron/Graphite/B systems). Synergetic effects producing maximum values in friction coefficient (μ)‐composition curves were not found in all combinations. All combinations of lubricant/lubricant and abrasive/abrasive reduce μ and the effects of the combinations of abrasive/lubricant are dependent upon their abrasive or lubricant efficiency. Strong abrasive (Al2O3) plays an important role on the formation of friction layer that the transferred iron from disc to friction materials in combinations of Al2O3/lubricant/B systems, and there is no such a transfer of iron from disc to friction materials on the surface of lubricant/lubricant combinations. The S type friction transition was observed in MoS2/steel wool/B and graphite/steel wool/B systems and was caused by adhesion friction mechanism.
Thermoplastic matrix phase transitions in a carbon fiber composite, studied by contact electrical resistivity measurement of the interface between two unbonded laminae
Authors: Mei Zhen , Chung D. D. L.
Published: April 2004

Measurement of the contact electrical resistivity of the interface between two unbonded laminae of a continuous carbon fiber thermoplastic (nylon‐6) matrix composite during heating provides a method of thermal analysis that is sensitive to the glass transition and melting of the thermoplastic matrix. The phase transitions result in peaks in the resistivity, due to matrix molecular movement.
Scrap tire/aggregate composite: Composition and primary characterizations for pavement material
Authors: Chung Kyung‐Ho , Hong Young‐Keun
Published: April 2004

A new type of pavement material using scrap rubber, the so‐called elastic and permeable pavement material (EPPM), was proposed in this study. EPPM is a new material to overcome water permeability and brittleness, which are defects of the conventional rubber asphalt and cement concrete, respectively. Those problems could be solved by introduction of grounded scrap rubber and structural design of EPPM. Results showed that key factors affecting the compressive strength and the water permeability of EPPM were the size of grounded scrap rubber and aggregate, the amounts and property of the binder. The optimum level of binder was about 8 wt%. The compressive strength and water permeability of EPPM were 1.1 and 116 times higher than those of conventional porous cement concrete, respectively.
Autoclave manufacturing of thick composites
Authors: Antonucci Vincenza , Giordano Michele , Imparato Sabato Inserra , Nicolais Luigi
Published: April 2004

Autoclave manufacturing of thermoset composites is determined mainly by heat transfer phenomena. As a matter of fact, the consolidation of composite laminates takes place by the progress of the polymerization, which is activated thermally. The design and control of the autoclave process relies on the capability to manage the relationship between the temperature‐pressure cycle of the heat carrier fluid and the temperature distribution through the manufacturing part. In particular, in industrial cases, the main limitations reside in the correct evaluation of the local convective heat transfer conditions through the autoclave and in the evaluation of the local thermal inertia arising from the bagging‐tooling system. In this study, the autoclave manufacturing of thick laminates has been addressed by modeling the heat transport phenomena occurring through the composite, the bagging and the tooling system. A new methodology for the evaluation of the energy transfer regimes has been proposed accounting for the heat fluxes from the bag and the tool side, the temperature through‐the‐thickness gradients and the heat generated by the resin polymerization reaction. The proposed approach enables the prediction of the temperature history of the autoclave assembly without knowledge of the effective thermal inertia of the two external layers, which could be difficult to evaluate owing to possible deformations of the bag during the manufacturing cycle and nonuniform shape of the metallic tool along the part. Experimental data from industrial autoclave runs have been collected and analyzed to validate the method.
Influence of heat transfer and curing on the quality of pultruded composites. I: Experimental
Authors: Li Shoujie , Ding Zhongman , Xu Liqun , Lee L. James , Engelen Herbert
Published: April 2004

Blister formation, a major concern in pultrusion, has not been studied in detail. The objective of this study is to investigate the mechanism of blister formation and the effect of process variables such as die temperature, pulling speed, die length, and composite thickness on blister formation. Dies with different length and a stop‐start method were used to investigate blister formation. The results show that for a given die and resin system, low temperature and a higher pulling speed lead to blister formation. Longer dies can prevent blister formation. Based on the experimental results, process windows for 4‐mm‐thick and 6‐mm‐thick composites are established for a vinyl ester resin. This study suggests that heater power input should be optimized in high‐speed pultrusion.
Influence of heat transfer and curing on the quality of pultruded composites. II: Modeling and simulation
Authors: Ding Zhongman , Li Shoujie , Lee L. James
Published: April 2004

In this study, a computer simulation code is developed to predict the dynamics of heat transfer in the pultrusion process. The die block and heater arrangement are included in the heat transfer analysis so that the simulation can provide the temperature profile at the interface between the die and the composite. The measured interface temperature profiles are then used to validate the simulation code. Energy management, i.e. heater power control along the heating die, is also considered in the simulation code. The code is capable of carrying out transient thermal analysis for both start‐up and steady‐state operation of the pultrusion process. From the experimental observations on the part quality in terms of blister formation, a processing window was obtained by showing the relation of the die length and the line speed to the part quality. The processing window is then generated numerically using the computer code based on the definition of a critical die length proposed in this work, and the result shows good agreement with the experimental data.
Effects of a chelating agent ‐ 2,4‐pentanedione on low temperature composite molding of vinyl ester and unsaturated polyester resins
Authors: Li Ling , James Lee L.
Published: April 2004

A major concern in low temperature composite manufacturing processes is how to design and control the mold filling and curing time. Inhibitors or retarders are often used to prevent premature gelation and provide a sufficiently long time to fill the mold completely. However, the addition of these chemical species tends to result in a low mold curing rate and a low final resin conversion. In this study, a chelating agent 2,4‐pentanedione (2,4‐P) was used to manipulate resin gelation and curing. This agent is known to affect the catalytic activity of the promoters (i.e. metal compounds such as cobalt carboxylates) in the decomposition of initiators. It can function as either a retarder or a co‐promoter in the co‐polymerization of styrene/polyester and styrene/vinyl ester resins depending on the acidity of the resin system. Based on this observation, an improved room temperature vacuum‐assisted resin transfer molding process was designed. This design allows 2,4‐P to serve first as a retarder during mold filling to achieve a long gel time, it then as a co‐promoter during curing to increase the curing rate. The 2,4‐P also increases the resin conversion as the acidity of the resin increases.
Effects of conductive fibers and processing conditions on the electromagnetic shielding effectiveness of injection molded composites
Authors: Yang S. Y. , Chen C. Y. , Parng S. H.
Published: April 2004

This paper investigates the electromagnetic interference shielding effectiveness (EMI SE) of injection molded ABS disks filled with stainless steel fibers (SSF) and nickel‐coated graphite fibers (NGF). The effects of fiber type, fiber length and weight percentage on SE were studied. Optical microscope (OM) and scanning electron microscopy (SEM) observations of the fiber distribution and dispersion were used to aid interpretation of the deviation on SE. The effects of processing conditions such as ring gate angles and injection speed on SE and fiber dispersions were also investigated. It is found that the SE of SSF filled disks is better than that of NGF with the same fiber length and weight percentage. The SEM shows that the SSF with severe twists connect with each other to form a three‐dimensional network. Nevertheless, the NGF break into straight fragments, which make it difficult to form networks. With the same type of fiber (SSF), the critical concentration of 6mm was similar to that of 4mm. But the SE of 6mm is a little higher than that of 4mm. Minor improvements of SE values were obtained with expanded ring gate angles. Gate design and injection speed both change filling patterns.
Effect of the microstructure of GMT on its mechanical properties
Authors: Zhao Ruofei , Zhou Xiaodong , Dai Gance
Published: April 2004

The effect of microstructure of GMT on its mechanical properties was investigated. The studied microstructure includes the fiber mat structure, the through‐thickness glass fiber content‐distribution of GMT sheets and the void content. The fiber bundle GMT (FB‐GMT) and the single fiber GMT (SF‐GMT) were prepared by the impregnation process using continuous fiber bundle mats and continuous single fiber mats as reinforcement, respectively. The mechanical properties of the two GMTs were compared to reveal the difference in reinforcing effect between the fiber bundle and the single fiber. The effect of needle density of the fiber mat on the mechanical properties of GMT was also studied, which indicated that needle‐punching improves the mechanical properties of GMT, and that the optimal needle density is 40∼60 needles/cm2. The through‐thickness glass fiber content‐distribution, which is inhomogeneous and can be modified by the film‐stacking method, significantly affects the mechanical properties of GMT. Finally, the study of the effect of void content indicated that with increasing void content, the strength and modulus of GMT decrease, but the impact property increases slightly.
Internal stress control in epoxy resins and their composites by material and process tailoring
Authors: Eom Yongsung , Boogh Louis , Michaud Véronique , Månson Jan‐Anders
Published: April 2004

The development of internal stress during cure of epoxy and hyperbranched polymer‐modified epoxy resins was characterized, taking into account the evolving viscoelastic properties, the volumetric shrinkage due to the chemical reaction, and the thermal expansion. A criterion for void formation during cure in a constrained mold was proposed, providing guidelines for the construction of a process window for manufacturing of void‐free composites. It was shown that the internal stress development in epoxy resins during cure is strongly influenced by the presence of hyperbranched polymer modifiers. The role of these modifiers was illustrated for the case of autoclave processing of glass fiber/epoxy composites. This study showed that higher fiber volume fractions could be used with hyperbranched polymer‐modified resins than with unmodified resins, for producing void‐free laminates. It also appeared that by suitable tailoring of the process cycle, a fully stress‐free laminate could be obtained after cure, using the modified resin.
Dual curing of carbon fiber reinforced photoresins for rapid prototyping
Authors: Gupta A. , Ogale A. A.
Published: April 2004

Photo‐thermal dual‐curing of a carbon fiber reinforced photoresin is reported in this study. The primary limitation of carbon fibers is that they are opaque to ultra‐violet (UV) light, and the resin present inside the carbon fiber tow remains uncured if only a photolytic mechanism is used. Therefore, a dual‐curing resin formulation was developed that consisted of acrylate ester of bisphenol A‐epoxy (primary resin), 1‐hydroxycyclohexyl phenyl ketone (a photoinitiator), and lauroyl peroxide (thermal initiator). The fibers were dispersed in the resin and photocured by UV radiation. Subsequently, the composites were thermally cured to solidify the resin present inside the fiber tow. Differential scanning calorimetry indicates that the thermal initiator activates at approximately 70°C. The dual‐cured composites, processed by a dip‐coating technique and also in a desktop photolithography unit, were tack‐free and fully solidified in the interior. Thus, it was established that by using a dualcuring resin formulation, the resin present outside and inside the carbon fiber tow could be cured to produce a carbon fiber reinforced photoresin. Such a reaction scheme has application in composite photolithography where incorporation of carbon fibers into photopolymers can enhance electrical and thermal conductivities of rapid tooling materials.
Structure–tensile property relationship of knitted fabric composites
Authors: Bini T. B. , Ramakrishna S. , Huang Zheng Ming , Lim C. T.
Published: April 2004

This paper reports some further studies on the tensile properties of plain weft knitted DuPont Kevlar fiber fabric reinforced epoxy matrix composites. One aim of this work is to investigate systematically the anisotropy of knitted fabric composites. Tensile tests were conducted at different off‐axial angles (0°, 30°, 45°, 60° and 90°) with respect to the wale direction. Fracture modes corresponding to this off‐axial variation were clearly identified. The elastic modulus and tensile strength were found to be the highest in the wale direction (0°), but decreased gradually towards the course direction (90°). This anisotropic study was carried out on both single layered and multilayered (four layered) knitted fabric composites. Another aim is to study the effect of specimen width (or number of loops per specimen width) on the tensile properties. This study indicated an optimum number of loops per sample width required to obtain meaningful tensile test results. Further, edge effect on the tensile properties of the knitted fabric composites was also investigated in the paper. This was achieved through comparative studies on cut and uncut four layered specimens. In the cut specimens the continuity of the yarns is lost at the cut edges, which show a marginal variation in the properties compared with the uncut specimens where the yarns are continuous throughout the specimen. Finally, a study was also carried out to investigate the effect of loop size (or stitch density) on the tensile strength and stiffness of the single layered composites.
Modification of some mechanical properties of spruce by radiation induced copolymerization of acrylonitrile and methyl methacrylate with allyl glycidyl ether
Authors: Şolpan D. , Güven O.
Published: April 2004

In this study, spruce samples were impregnated with acrylonitrile (AN), methyl methacrylate (MMA), allyl glycidyl ether (AGE), AGE/AN or AGE/MMA monomers and monomer mixtures. In situ polymerization (copolymerization) was achieved by gamma irradiation. The relationship between the mechanical properties of the wood‐polymer(copolymer) composites and the kind and quantity of polymers and copolymers, irradiation dose and artificial aging treatment of the wood was investigated. The fine structure of wood‐polymer(copolymer) composites was determined by Scanning Electron Microscopy. The presence of homopolymer and copolymers increased the mechanical properties of the wood. The compressive strength and Brinell Hardness Numbers, determined for untreated and treated wood samples, indicated that the mechanical strength of wood‐polymer (copolyrner) was significantly increased in the presence of P(AGE/MMA). At maximum percent conversion, the percentage increase in the compressive strength with regard to the applied force perpendicular to the fibers in spruce was 218%. After aging for 28 days, it was found that there were no significant changes in mechanical stability.