bluuebunny/crossref_metadata_2025 huggingface dataset:
The effect of maleated compatibilizers on the structure and properties of EVOH/clay nanocomposites
Authors: Artzi N. , Nir Y. , Narkis M. , Siegmann A.
Published: April 2004

The effect of compatibilizers on the blending torque, crystallization behavior, intercalation level, thermal stability and morphology of EVOH/treated clay systems was investigated. Maleic anhydride‐grafted ethylene vinyl acetate (EVA‐g‐MA) or maleic anhydride‐grafted linear low density polyethylene (LLDPE‐g‐MA) were used as compatibilizers of EVOH with clay, in various concentrations (1, 5 and 10 wt%). The blends were processed using Brabender Plastograph and characterized by XRD, SEM, DSC, DMTA and TGA. X‐ray diffraction shows advanced intercalation within the galleries when the compatibilizers were added. Unique results were obtained for the EVOH/clay/compatibilizer systems, owing to a high level of interaction developed in these systems, which plays a major role. Thermal analysis showed that with increasing compatibilizer content, lower crystallinity levels result, until at a certain content no crystallization has taken place. Significantly higher viscosity levels were obtained for the EVOH/clay blends compared to the neat polymer, as seen by a dramatic torque increase when processed in the Brabender machine. The DMTA spectra showed lower Tg values for the compatibilized nanocomposites compared to the neat EVOH and the uncompatibilized composites. Storage modulus was higher compared to the uncompatibilized EVOH/clay blend when EVA‐g‐MA compatibilizer was added (at all concentrations), and only at low contents of LLDPE‐g‐MA. TGA results show significant improvement of the blends thermal stability compared to the neat EVOH, and to the uncompatibilized blend, indicating an advanced intercalation.
Laser drilling of liquid crystal polymer composite
Authors: Yue T. M. , Chan K. C.
Published: April 2004

This investigation studies the laser machining behavior of a glass fiber reinforced liquid crystalline polymer (LCP) composite by using two different types of lasers, namely; pulsed Nd:YAG and excimer. A theoretical model is established to predict the maximum depth‐of‐drill of the YAG laser machined holes. Moreover, the effects of the YAG laser output parameters on the geometry and the quality of the machined surface of the hole are discussed. The laser machining characteristics of the composite are compared for the two different types of lasers in terms of laser absorptivity. The results show that the glass fiber reinforced LCP has a higher absorption towards UV radiation than infrared light. Scanning electron microscopy examinations were also conducted to assess the surface quality of the machined holes. In YAG laser drilling, a high pulse energy or excessive pulses caused severe carbonization of the surface, and many cracks formed. On the other hand, excimer laser did not cause any significant carbonization of the surface; however, a large number of voids were found in the process affected zone.
Processability and properties of novel glass‐polymer melt blends
Authors: Otaigbe Joshua U. , Quinn Candace J. , Beall George H.
Published: April 2004

Dynamic mechanical analysis was used to study the viscoelastic properties of two novel highly filled phosphate glass‐polymer melt blends to accelerate efforts to optimize their melt processing. The melt of one blend was thermally stable while that of the other blend was not, as evidenced by modulus growth over time of the latter. The frequency dependencies of storage and loss moduli for both blends at 400°C showed evidence of incomplete relaxation. Recrystallization, formation of some fibrillar structures within the polymer phase during flow, transesterification of the polymer phase, or interactions between the polymer and glass are thought to be responsible for the observed differences between the viscoelastic properties of the two blends.
The gradient of mechanical characteristics across the thickness of composite laminates after exposure to a low earth orbit environment
Authors: Startsev Oleg V. , Isupov V. V. , Nikishin E. F.
Published: April 2004

This paper deals with a complex investigation of carbon and glass fiber reinforced plastics (CFRP, GFRP) and hybrid composites based on epoxy compositions and used in Salyut‐type spacecraft that had spent up to 1501 days in outer space. The samples with an unprotected surface and the samples exposed to outer space under the different screens have been explored. In the paper, results on thin measurements of dynamic shear modulus, Young's modulus, linear thermal expansion coefficient, glass transition temperature, and microhardness of the carbon plastics KMU‐31, KMU‐41, and glass plastics VPS‐7V are presented. Results show that thermal cycling of composite laminates in space, with a temperature difference of 200 K between the sunlit side and the reverse side, generates the gradient of mechanical properties across the plate thickness. Particular attention is given to the problem of thin layer measurement methodology and to the working out of experimental results. There are requirements for ground simulation research of composite laminates providing the same character of thermal cycling as in a low earth orbit, LEO. Some criteria are suggested for test equivalence, according to the data of dynamic mechanical analysis (DMA), linear dilatometry (LD), and microhardness.
Determination of corner and edge permeability in resin transfer molding
Authors: Sheard J. , Senft V. , Mantell S. C. , Vogel J. H. , Maier R. S.
Published: April 2004

Resin flow in resin transfer molding may be strongly influenced by small heterogeneities in the fiber preform, such as narrow channels formed by bending and fitting into a mold. An evaluation of preform permeability in these regions of nonuniform packing is presented. The study incorporates an empirical and analytic approach to iteratively determine the permeability in these regions. Flowfront data were recorded for high fiber volume fraction woven fiber preforms. Edge gap width, injection pressure, and fiber volume fractions were varied. The flow front data were compared with numerical simulations to estimate enhanced permeability at the edges. The results indicate that, for high fiber volume fraction preforms, flow in the channel dominates for relatively small (≈ 2 mm) gaps.
Barium sulfate–filled blends of polypropylene and polystyrene: Microstructure control and dynamic mechanical properties
Authors: Hammer Claes O. , Maurer Frans H. J.
Published: April 2004

The microstructure of filled blends consisting of a semicrystalline polypropylene homopolymer (PP) matrix and a polystyrene (PS) dispersed phase with barium sulfate (BaSO4) filler can be controlled by an addition of maleic anhydride‐grafted polypropylene (PP‐g‐MAH) or styrene‐maleic anhydride copolymer (SMA). Scanning electron microscopy (SEM) and dynamic mechanical analysis (DMA) in the solid and melt states were the analytical tools used. The filler is occluded at the interface of the polymer phases in the filled blend without PP‐g‐MAH or SMA. The addition of BaSO4 to the PP/PS blend results in a decrease in domain size of the minor polymer phase. The filler is occluded in the PP phase when PP‐g‐MAH is added, while SMA results in the occlusion of the barium sulfate filler in the PS phase. The results of the SEM and the DMA studies were correlated, with indications of a filler network structure with both the PP‐g‐MAH and SMA modifiers. The barium sulfate filler surface has a specific affinity to maleic anhydride copolymers. The BaSO4 filler alone did not have a nucleation effect on the PP; however, in combination with PP‐g‐MAH, a clear nucleation effect was observed.
Production and characterization of innovative carbon fiber–polycarbonate composites
Authors: Caldeira G. , Maia J. M. , Carneiro O. S. , Covas J. A. , Bernardo C. A.
Published: April 2004

Vapor Grown Carbon Fiber (VGCF)–polycarbonate composites were produced using conventional processing and the performance of the parts thus produced was evaluated. The tensile properties of the composites were only marginally better than those of the nonreinforced polymer, and the impact resistance decreased with the incorporation of the fibers. In an attempt to understand this behavior, the rheological characteristics of the composites were studied, using rotational (steady and oscillatory) and capillary rheometry. A decrease in viscosity with fiber content was observed and explained in terms of poor fiber‐matrix adhesion. Evidence of possible weak fiber structures forming above a critical concentration was also found.
Resin transfer molding (RTM) with toughened cyanate ester resin systems
Authors: Rau A. V. , Srinivasan S. A. , McGrath J. E. , Loos A. C.
Published: April 2004

This investigation explored the feasibility of recently developed toughened cyanate ester networks as candidate materials for high performance composite matrix applications. The resin investigated was a bisphenol‐A cyanate ester toughened with hydroxy functionalized phenolphthalein based amorphous poly(arylene ether sulfone). A series of four toughened cyanate ester resins were generated by varying the concentration and the molecular weight of the toughener. The thermoplastic modified toughened networks exhibited improvement in the fracture toughness over the base cyanate ester networks without significant reductions in mechanical properties or glass transition temperature. Carbon fabric composite panels were manufactured by liquid molding processes (resin transfer molding and resin film infusion) with the untoughened and toughened cyanate ester resin systems. The panels were subjected to physical, impact damage, and fracture toughness tests. The results of physical testing indicate consistently uniform quality, and the maximum void content was found to be less than 2%. The toughened cyanate ester composites exhibited significantly improved impact damage resistance and tolerance compared with hot‐melt epoxy systems. A marked increase in the mode II composite fracture toughness was observed with an increase in the concentration and the molecular weight of the toughener.
Pultrusion die pressure response to changes in die inlet geometry
Authors: Sharma D. , McCarty T. A. , Roux J. A. , Vaughan J. G.
Published: April 2004

Pultrusion is a process of manufacturing composites that requires a high resin pressure rise in the tapered die inlet region. A sufficiently high pressure rise is important for a good quality pultruded product, thereby necessitating a study of the mechanisms affecting the die inlet pressure rise. Various process control parameters affect the resin pressure rise in the die inlet. The geometry of the tapered die inlet region can have a significant effect on the pressure rise in the pultrusion die. In this study a finite element model was developed to predict this pressure rise as a function of the tapered die inlet geometry. The composite matrix being pultruded was modeled on the assumptions of Darcy's laws for flow in porous media. A Galerkin's weighted residual based finite element technique was used to solve the governing equations. The pressure rise in the tapered inlet region of the die, as well as in the straight portion of the die, is predicted by this finite element model. Circular, parabolic, and wedge shaped die inlets have been modeled to compare their shapes on the resin pressure rise in the pultrusion die. Different angles for wedge shapes, different radii for circular shapes, and different foci for parabolic shapes were modeled to predict the influence of varying key geometrical parameters for each die inlet contour on pressure rise. The finite element model developed provides insight as to how to design the die inlet to produce a suitable pressure rise in the pultrusion die inlet.
Extrusion and mechanical characterization of PVC‐leather fiber composites
Authors: Madera‐Santana Tomás J. , Torres Alberto Campos , Lucero Alfredo Márquez
Published: April 2004

Every year great quantities of chrome tanned leather wastes produced by the footwear and clothing industries are buried or burned. These practices produce several contaminants that are released into the environment. An alternative to disposing of these wastes is to reuse them. In this work, a method to use these wastes as filler in a polymer matrix is proposed. Also, a technique for processing the composite obtained by continuous extrusion is demonstrated. To evaluate this technique, a series of PVC‐leather fiber composites were prepared and extruded through a flat die to produce sheets. The process produced a leather‐like sheet that could be used in several applications. The influence of the filler content on the processability and the final properties of the composite sheets were evaluated. The tests revealed that the sheets are flexible and exhibit sufficient water absorption to be suitable for several applications in the footwear and clothing industry. Finally, the tests show that this composite can be formulated and processed at high productivity levels and at a low cost.
Power issues in the manufacturing and characterization of polymers and composite materials
Authors: Buehler Frédéric U. , Seferis James C.
Published: April 2004

Dynamic Mechanical Analysis (DMA), although utilized for more than three decades, has been restricted so far to material characterization rather than processing. Recently the importance of power for describing viscoelasticity in prepreg process operations has been demonstrated. This present work views DMA as an integral part of the power analysis of processes. In this study, four types of prepreg were produced under the same power of impregnation utilizing epoxy resins with various PEI contents. Prepregs were tested for compressive and toughness power as well as loss power. Laminates were developed and analyzed by DMA. DMA data was treated according to the established power methodology and compared with the tack power of the original prepreg. Specific compressive power was generally found to increase with increasing storage DMA power, while specific toughness power was found to show the opposite trend. The inverse of power, defined as tolerance, was also investigated. The out‐of‐phase DMA tolerance was found to correlate to loss prepreg power, bringing a deeper understanding to the fundamentals of viscoelasticity formation. This analytical methodology can be applied beneficially to many topics to provide a better understanding of polymers and composites, as well as smart materials.
Crystalline morphology in high‐density polyethylene/paraffin blend for thermal energy storage
Authors: Lee Chang Hyung , Choi Hyeong Ki
Published: April 2004

The durability of high‐density polyethylene (HDPE)/ paraffin blends as a thermal energy storage material was studied by investigation of the seepage behavior of paraffin. The HDPE in the blends serves to prevent paraffin seepage during repeated heating‐cooling cycles; i.e., the HDPE acts as a sealant material. Two representative HDPEs were used for the blends; one was a low molecular weight HDPE (1‐HDPE) and the other was a high molecular weight HDPE (h‐HDPE). Investigation by optical microscopy, scanning electron microscopy and light scattering revealed that the surface area of an injection molded sample in h‐HDPE/paraffin blend had compact spherulites of about 7 μm in radius. On the other hand, the morphology of the coarse spherulite of about 15 μm in radius is observed in the 1‐HDPE/paraffin blend. This crystalline morphological characteristic resulting from the molecular weight difference of the sealant material (HDPE) is responsible for the excellent sealant property of the h‐HDPE/paraffin blend.
Effect of heating on the structure of carbon fiber polyphenylenesulfide‐matrix composite, as studied by electrical resistance measurement
Authors: Mei Zhen , Chung D. D. L.
Published: April 2004

Heating and cooling were found to affect the structure of carbon fiber polyphenylenesulfide‐matrix composites, as shown by their effects on the DC electrical resistance of the composite in the fiber direction. Matrix flow during first heating above Tg and thermal stress buildup during cooling in any thermal cycle caused the resistance to increase, whereas isothermal crystallization at 180°C caused the resistance to decrease. Thermal stress buildup was reversible upon thermal cycling. Prior annealing at 180°C diminished the matrix flow because of improved fiber‐matrix bond, and it increased the matrix crystallinity. Annealing at 180°C for 15 h or more was sufficient to eliminate the matrix flow.
Mechanical properties of parts manufactured from prestaged thermosetting towpreg
Authors: Beck R. W. , Colton J. S.
Published: April 2004

A prestaging process consisting of passing thermoset towpreg through a tunnel oven and roller apparatus was developed to address the difficulties inherent in making thick‐walled thermosetting composite parts: aging, moisture uptake, and low resin viscosity during lay‐up; and residual stresses, warpage, thermal degradation, and excessive void nucleation during the final cure. Unidirectional laminates were fabricated from prestaged and as‐received AS4/3501‐6 towpregs to understand the relationship between the parts' mechanical properties and the amount of prestaging (degree of cure) of the towpregs. In this manner, the feasibility of manufacturing with prestaged thermosetting towpreg was confirmed. Ultrasonic nondestructive evaluation showed that the parts manufactured from prestaged towpreg were uniform and relatively low in voids as compared to parts manufactured with as‐received towpreg. This was confirmed with scanning electron microscopy. Using three‐point bending tests, a drop in mechanical properties was found in parts manufactured from towpreg prestaged beyond 19% degree of cure. However, the parts were well consolidated and had predictable mechanical properties up to approximately 40% degree of cure. The equivalent limits on degree of cure from a companion processing study are between 15% and 22%.
Effects of preferential encapsulation of glass fiber on the properties of ternary GF/PA/PP blends
Authors: Maeng Yoo Jae , Yoon Byung Seon , Suh Moon Ho , Lee Suck Hyun , Im Wan Bin
Published: April 2004

Long fiber molding materials are expected to play an important role in the near future. This paper describes a series of experiments performed to examine properties of ternary blends containing glass fiber (GF), polyamide (PA), and polypropylene (PP). The continuous glass fiber was impregnated with one of the blend constituent polymers by our specially designed impregnation apparatus and cut into chips of 6 mm length. These chips and the other polymer were used to produce various testing specimens in a twin screw extruder or in injection molding machine. The results indicated that the effect of fiber addition on the mechanical and rheological properties is clearly dependent on the order of impregnation process. In the blends containing the GF/PA + PP, the GFs are preferentially encapsulated with PA, and therefore the mechanical properties are superior to the blends with the GF/PP + PA in which the PP phase is located surrounding the GFs. This improved wetting of fibers by sequential impregnation not only resulted in better properties but also protected the fibers from shear action of the screw, thereby allowing significant increase in average fiber length to be achieved in the injection molding process.
Interfacial properties of regenerated cellulose fiber/polystyrene composite materials. Effect of the coupling agent's structure on the micromechanical behavior
Authors: Trejo‐O'reilly J. A. , Cavaillé J. Y. , Paillet M. , Gandini A. , Herrera‐Franco P. , Cauich J.
Published: April 2004

The interfacial properties of polystyrene/regenerate cellulose fiber composite materials are characterized using micromechanical tests such as the single fiber fragmentation and microbond (“microdrop test”). The cellulose fibers were grafted with different copolymers of different chemical structures as well as different molar masses ranging from 300 to 18,000 (ASA, jeffisocyanate, commercial poly)styrene‐co‐maleic anhydride and “home‐made” poly(styrene‐co‐TMI). The two polystyrene based copolymers have been shown to be miscible with polystyrene. It was found that the higher improvement of the interfacial shear strength was obtained when the fiber is grafted with the higher molecular weight, i.e., the poly(styrene‐co‐TMI).
Rheology, morphology and properties of LCP/Nylon 66 composite fibers
Authors: Wang Humin , Lee Kah Wee , Chung Tai‐Shung , Jaffe Michael
Published: April 2004

The rheology, morphology and properties of the composite systems of LCP, Vectra ATM 950 and Nylon 66 were investigated. The viscocity ratio of LCP and matrix has strong influence on their morphology. For LCP blends, the viscosity ratio of LCP is a critical factor in determining the blend morphology. The optical micrographs show that the good fibrillation can be achieved when the viscocity of the dispersed LCP phase is less than that of the Nylon 66 matrix at 310°C. The dispersed LCP domains tend to be spherical or cluster‐like when the viscosity ratio of the disperesed LCP phase and the Nylon 66 matrix is more than 1 at 280°C. The scanning electron microscopy (SEM) and optical micrograph observations show that Nylon 66 is immiscible with LCP, and there are two distinct phases in the blends. The morphology of LCP phase changes with the composition. LCP exhibits a fine fibril dispersed phase in the Nylon 66 matrix in the low LCP concentration. With an increase in LCP concentration, the morphology of LCP phase is changed form a fine fibril dispersed phase to a perfectly aligned continuous fiber reinforced phase in the rich LCP concentration. The tensile moduli increase with LCP concentration, especially in the rich LCP concentration. The tensile strengths increase with LCP concentration only when LCP concentration is above 40 wt%. Compared to the pure Nylon 66 fiber, the 40 wt% LCP composite sample shows a 982.1% increase in tensile modulus and a 123.3% increase in tensile strength. The mechanical properties of composite fibers are below the rule of mixtures if the LCP concentration is low, but above the rule of mixtures if the LCP concentration is high.
Mode I fracture resistance characteristics of graphite/epoxy laminated composites
Authors: Rhee K. Y. , Koh S. K. , Lee J. H.
Published: April 2004

Mode I crack resistance behavior of fiber‐reinforced (graphite/epoxy) composites laminated unidirectionally and anti‐symmetrically was studied. Double cantilever beam (DCB) specimens of stacking sequences, [O12//O12] and [(O/90)3s//(90/O)3s] were used where // represents the initial crack location. Resistance curves (R‐curves) were constructed for three initial crack lengths in order to determine the effects of initial crack length on the resistance behavior. The resistance force, GR, for a crack increment was determined from the compliance calibration method. The results show that for the case of [(O/90)3s//(90/O)3s], the initial crack deviated from the midplane and propagated in a zigzag fashion within 13th(90‐deg), while the crack propagated along the midplane for a [O12//O12] case. The results also show that for both cases, GR was affected by the initial crack length before GR was stabilized. However, GR was not affected by initial crack length when GR was stabilized for each case.
Relationship between scale effect and structure levels in fibrous structures
Authors: Pan Ning , Zhao Shumin , Hua Tao
Published: April 2004

A series of testing samples of fibers, yarns, fabrics, and coated fabrics of the same source were prepared and then tested at constant strain rate but different gauge lengths on an Instron tester for tensile test. The results are compared to see the scale effect at different structure levels of fibrous materials. Discussions and explanations of the data are provided as well.
Effects of chemical composition and thermal stability of finishes on the compatibility between glass fiber and high melting temperature thermoplastics
Authors: Gao P. , Ward Yanling , Su K. B. , Weng L. T.
Published: April 2004

Experimental studies were made on the surface characteristics of glass fibers with two different finishes. The effects of the chemical composition and thermal stability of the finishes on the compatibility between glass fibers and high melting temperature thermoplastics were investigated. Thermogravimetric Analysis (TGA) was used to characterize the composition of surface finishes and their thermal stability. The chemical composition of surface finishes was investigated using a combination of X‐ray photoelectron spectroscopy (XPS) and Time‐of‐Flight secondary ion mass spectrometry (ToF SIMS). Static contact angle measurements were performed at room temperature to characterize the interfacial tension between the glass fibers and thermoplastics. The study provides a fundamental understanding on some important compatibility issues between thermoplastic resins and glass fiber related to composite fabrication and application.
The occurrence of surface roughness in gas assist injection molded nylon composites
Authors: Liu Shih‐Jung , Chang Jer‐Haur
Published: April 2004

Gas assist injection molding has increasingly become an important industrial process because of its tremendous flexibility in the design and manufacture of plastic parts. However, there are some unsolved problems that limit the overall success of this technique. The purpose of this report was to study the surface roughness phenomenon occurring in gas assist injection molded thermoplastic composities. The materials used were 15 % and 35% glass‐fiber filled nylon‐6 composites. Experiments were carried out on an 80‐ton injection molding machine equipped with a high‐pressure nitrogen‐gas injection unit. Two “float‐shape” axisymmetric cavities were used. After molding, the surface quality of molded parts was measured by a roughness meter. Various processing variables were studied in terms of their influence on formation of surface roughness: melt temperature, mold temperature, melt filling speed, short‐shot size, gas pressure, and gas injection delay time. Scanning electronic microscopy was also employed to characterize the composites. It was found that the surface roughness results mainly from the exposure of glass fiber in the matrix. The jetting and irregular flows of the polymer melt during the filling process might be factors causing the fiber exposure.
Mode II interlaminar fracture behavior of carbon bead‐filled epoxy/glass fiber hybrid composite
Authors: Lee Jung Ju , Lim Jeong Ok , Huh Jeung Soo
Published: April 2004

To investigate the effect of including carbon beads on the mechanical properties of epoxy resin, the fracture toughness of carbon bead‐filled epoxy was earlier evaluated using a CT (compact tension) specimens and Mode I fracture toughness was observed. Based on those results, in this study, the Mode II interlaminar fracture toughness of carbon bead filled epoxy/glass fiber hybrid composites was evaluated using end notch flexure (ENF) specimens. The hybrid composites showed increased Mode II interlaminar fracture toughness. The optimal bead volume fraction was around 15%.
Characterization and design of interphases in glass fiber reinforced polyproplyene
Authors: Mäder E. , Pisanova E.
Published: April 2004

Bond strength between reinforcing fibers and polymer matrices can be controlled in two ways: 1) by intensification of molecular interaction at the interface and 2) by creation of a strong transition layer (interphase) between the components. In this paper, we consider the possibilities of controlling interfacial strength by means of target‐oriented variation of structure, thickness and strength of the interphase artificially created between the glass fiber and the polypropylene matrix. The bond strength was measured using a continuously monitored microbond test, including recording the crack length as a function of the load applied. The measured interfacial strengths correlated to the macromechanical properties of glass fiber reinforced polypropylene. The interphase design provided simultaneous increase in the tensile strength and the impact toughness of the composites.
Influence of PANI‐complex on the mechanical and electrical properties of carbon fiber reinforced polypropylene composites
Authors: Taipalus R. , Harmia T. , Friedrich K.
Published: April 2004

The aim of this work was to determine the influence of PANI‐complex on the mechanical and electrical properties of CF‐PP composites. As expected, an increase in tensile strength and modulus of the PP matrix could be achieved with an increasing fiber weight fraction. On the other hand, the PANI‐complex decreased the tensile strength and modulus of the fiber reinforced composites; however, these values remained on a better level than the value of the neat PP. Further, by using a long carbon fiber (LCF) reinforcement instead of short carbon fibers (SCF) the percolation threshold was moved towards a lower fiber weight content. In addition, a synergy effect between PANI‐complex and LCF in the PP‐matrix regarding the electrical properties occurred. In particular, an abrupt decrease in the surface resistivity could be avoided. Also, the surface resistivity of a blend is better when the blend consists of both PANI‐complex and LCF instead of only one of these fillers.
Thermoforming of reinforced thermoplastic stiffened structure
Authors: Nowacki J. , Neitzel M.
Published: April 2004

For thermoforming of continuous fabric reinforced thermoplastics, fabric shearing is the dominant deformation mode. The maximum shearing angle depends on the textile architecture and it is expressed as a locking angle, i. e., the smallest possible angle between warp and weft yarns. Wrinkling and buckling occur when the locking angle is exceeded or when too high compression stresses are introduced in the fabric during forming. To avoid these undesired effects membrane stresses must be introduced into the fabric, e.g., by using blankholders. In the first part of this paper a new pneumatic clamping device will demonstrate the advantages of easy handling and flexible force variation. The second part deals with a technology to form and join continuous fiber reinforced fabrics in one step: Tailored Blank Technology. This method reduces the manufacturing steps and offers the advantage to produce parts with different thicknesses or to add profiles and inserts to the main sheet. First results about the temperature windows will be discussed for glass fiber reinforced polypropylene.
Low velocity impact response of GFRP laminates subjected to cycling moistures
Authors: Li Guoqiang , Pang Su‐Seng , Helms Jack E. , Ibekwe Samuel I.
Published: April 2004

The low velocity impact response of laminated composites in ambient hygrothermal environments has been extensively investigated. This response, however, is not well understood when subjected to moisture cycling at elevated temperatures. In this current study, two types of glass fiber reinforced plastic (GFRP) laminates, unidirectional and crossply, were conditioned in a conditioning chamber for a maximum of eight moisture cycles at conditioning temperatures from 50°C to 100°C. Low velocity impact tests were conducted on the conditioned specimens and control specimens via an instrumented drop‐weight impact testing machine. The tension after impact (TAI) strength was investigated using an MTS machine. The equivalent damage size is obtained using an average stress criterion found in the literature. The effect of moisture cycling and conditioning temperatures on the low velocity impact response and residual load carrying capacity of GFRP laminates are evaluated via the test results.
Glass transition and melting behavior of carbon fiber reinforced thermoplastic composite, studied by electrical resistance measurement
Authors: Mei Zhen , Chung D. D. L.
Published: April 2004

DC electrical resistance measurement was applied to investigate the glass transition and melting behavior of carbon fiber reinforced nylon‐6 composite. The electrical resistance exhibited temperature dependencies that were attributed to the matrix molecular movements associated with structural transitions. The electrical resistance was affected by the degree of crystallinity and the thermal oxidative degradation, which were governed by the thermal history. The resistance results are consistent with differential scanning calorimetry (DSC) results. The resistance is more sensitive to the glass transition than DSC.
An analytical approach to evaluate the coefficients of thermal expansion of textile composite materials
Authors: Gowayed Yasser , Zou Weiqun , Gross Steven
Published: April 2004

An analytical approach is developed to evaluate the coefficients of thermal expansion (CTE) of textile reinforced composites. At the micro level, a cylindrical composite model is employed to model the fiber/matrix thermal and mechanical interactions. The effects of voids and fiber coating on the thermal expansion coefficients of composites are considered at this level. The cylindrical model was then embedded in a macro hybrid finite element solutio structure to calculate the value of the CTE for textile composites. AS‐4/epoxy balanced plain weave textile composites were manufactured. Five different fiber volume fractions were tested for CTE. Evaluatio of the thermal expansion coefficients using the current model was compared to experimental data for in‐plane and out‐of‐plane directions.
Rheological behavior of (short) carbon fiber/thermoplastic composites. Part I: The influence of fiber type, processing conditions and level of incorporation
Authors: Carneiro O. S. , Maia J. M.
Published: April 2004

The aim of this work is to understand the influence of type of (short) carbon fibers, processing conditions and fiber incorporation level on the rheological behavior of carbon fiber/polypropylene (PP) composites. For this purpose, two types of fibers (sub‐micron Vapor Grown Carbon Fibers, VGCF, and ex‐PAN, PAN), three different extruder screw geometries and three different fiber incorporation contents were studied. The rheological characterization was performed by means of capillary and rotational rheometry, results being presented and discussed in terms of reinforcing capability in both shear (steady and oscillatory) and extensional flows. The results show that VGCF have a generally higher influence on the rheological behavior of the composites than the PAN fibers. However, because of their higher intrinsic rigidity, PAN fibers give rise to composites with better mechanical properties than the VGCF ones. It is also shown that the influence of the screw geometry on fiber damage and, consequently, on the behavior of the composites, is weak, fiber degradation occurring mainly in the compounding stage. The incorporation level has the expected influence, i.e., it produces gradual changes in all the properties considered in this study.
Lignin reinforced rubber composites
Authors: Setua D. K. , Shukla M. K. , Nigam Vineeta , Singh Harjeet , Mathur G. N.
Published: April 2004

Lignin, a renewable waste material of pulp and paper industries, was analyzed through Fourier‐Transform Infrared Spectroscopy (FTIR) and found to be structurally similar to kraft lignin. Surface modification by addition of benzoyl peroxide and subsequent heating at 70°C caused generation of new functional groups in lignin. Efficacy of the crude lignin as well as that of the modified variety as a filler in nitrile rubber (NBR) has been evaluated. Rubber vulcanizates were analyzed for physico‐mechanical properties, oil and fuel resistance, and thermal stability, and compared with conventional fillers like phenolic resin and carbon black. Modified lignin has been found to produce superior elongation, hardness and compression set properties compared to phenolic resin but inferior to carbon black. Resistance to swelling, however, depends on the type of oil or fuel, and modified lignin always showed better properties than carbon black. Both thermo‐gravimetric analysis (TGA) and thermo‐mechanical analysis (TMA) showed highest thermal stability for the modified lignin followed by phenolic resin and carbon black.
Flow induced fiber orientation in compression molded glass mat thermoplastics
Authors: Nilsson Greger , Ericson Mats L. , Anders Holmberg J.
Published: April 2004

This study examines how the mechanical properties in GMT are affected by axisymmetric flow during compression molding. Two types of GMT with different architecture are used, swirled mat and short fiber GMT. Tree different grades are tested for each fiber architecture 20, 30, and 40% fiber content by weight. These are in principle the grades of GMT commercially available today. It is found that the flow reduced the tensile strength by 30 to 50% and the tensile modulus up to 30% in the flow direction. The reduction in mechanical properties, which is mainly caused by flow‐induced fiber orientation, is larger at high fiber contents. The study also showed that there is no major difference in behavior between swirled mat and short fiber GMT regarding flow induced fiber orientation.
Failure mechanisms in polypropylene with glass beads
Authors: Sjögren B. A. , Berglund L. A.
Published: April 2004

The effect of glass beads on the stress‐strain behavior of isotactic polypropylene has been examined. Poisson's ratio and secant compliance as a function of strain have been measured. Both sets of data are consistent with interfacial debonding as the initial damage mechanism. Interfacial debonding is then followed by extensive plastic yielding of the matrix at the debond sites. The maximum stress and strain to failure decrease with glass bead content and glass bead diameter. Impact properties correlate with the ability of the composites to reach high strain to failure. The proposed failure mechanisms are supported by fractography and in‐situ deformation studies by scanning electron microscopy.
Prediction of failure initiation in polypropylene with glass beads
Authors: Asp L. E. , Sjögren B. A. , Berglund L. A.
Published: April 2004

The effect of glass bead content and residual stresses on failure initiation in isotactic polypropylene composites has been investigated by finite element analysis for the cases of interfacial debonding, plastic yielding, and cavitation. Residual thermal stresses are demonstrated to have a large effect on global failure initiation stress. Yielding and cavitation occur at higher global stresses than debonding. Modeling results, as well as previous experimental data, support debonding as the initial failure mechanism.
Viscoelastic effects related to residual thermal stresses in bismaleimide/carbon fiber composite laminates
Authors: Sala Giuseppe , Di Landro Luca
Published: April 2004

This paper studies the effects of the residual stresses which originate in the laminates made of composite materials owing to the curing process, and on stresses affected by time and temperature. In order to sustain high operating temperatures, the polymer composites' laminates are made of high performance matrices that usually require processing cycles at high temperatures. The strong thermal variation due to the subsequent cooling process induces residual stresses, owing to the thermoelastic orthotropy of the material. For non‐symmetrical stacking sequences, these stresses notably modify the shape of the laminate and reduce both its static strength and buckling load, as a consequence of the latent content of elastic energy stored by the pre‐loading.

The polymeric composites show a viscoelastic behavior, which implies a constitutive law dependent on both time and temperature. For this reason, the analysis of the phenomenon should account for the creep and the relaxation mechanisms. The configuration of asymmetric laminate is evaluated by both analytical and numerical finite element (FEM) methods. The actual shape of laminates of different geometries is also experimentally determined. On the basis of the analysis of the shape of laminates measured after different thermal cycles, the evolution of residual stresses with time and temperature is analyzed.
Notch sensitivity and damage mechanisms of glass mat reinforced polypropylene
Authors: Lindhagen J. , Berglund L.
Published: April 2004

Notch Sensitivities of two structurally different glass‐mat reinforced polypropylene materials (GMT) were investigated. Center hole notches in tensile specimens were used in the tests. The results show that the short fiber material has higher unnotched strength, but also higher notch sensitivity compared to a swirled mat material. Reasons for this are discussed, focusing on microstructural differences. Predictions from four different failure criteria were compared with the experimental notched strength data. The point stress and damage zone criteria were found to give the best descriptions.
Effect of a filler on the long‐term mechanical behavior of an epoxy matrix/mineral particle composite
Authors: Hristova Julia , Minster Jiří
Published: April 2004

An analysis is provided for the continuous relaxation and retardation spectra of epoxy matrix composites filled with different amounts with marble micro‐particles. The particle size distribution is characterized by the diameter sampling medium d50 = 13 μm and the sampling quantile d97 = 80 μm. The concentration of this filler was 10, 29 and 44.5 vol%. The creep compliance and the relaxation modulus were determined from experimental results. Alfrey's method is used to define the continuous spectra from these long‐term (103 days) creep and stress relaxation data. A polynomial approximation is applied to the analytical form of the results. The influence of the filler fraction on the spectra's distribution and on the equilibrium values of relaxation moduli and creep compliances is discussed. The application of discrete relaxation and retardation spectra and the mutual transition between them are demonstrated using a Laplace transform.
The preparation and characteristics of low‐density polyethylene composites containing cellulose treated with cellulase
Authors: Kim Tae‐Jeong , Lee Young‐Mok , Im Seung‐Soon
Published: April 2004

Low‐density polyethylene (LDPE) composites containing untreated cellulose, cellulose treated with cellulase, and cellulose treated with cellulase after pretreating with NaOH were prepared. The purpose of the cellulase treatment of cellulose is to enhance the interfacial adhesion between the cellulose and the matrix. The effect of this treatment was studied by viscometry and X‐ray diffraction. Maleic anhydrideg‐polythylene (MAH‐PE) was also added to the composite to enhance interfacial interactions between the cellulose and the matrix and to increase the dispersibility and the wettability of cellulose. The increased adhesion in composites containing the treated cellulose and MAH‐PE was studied by FTIR. In addition, the thermal, dynamic mechanical, and tensile properties of the composites were investigated. When MAH‐PE was added to the composite, it was found that the reaction between MAH‐PE and treated cellulose occurred more easily.
Cationic cure of epoxy resins via benzylsulfonium salts covalently bound to glass surfaces
Authors: Mathias Lon J. , McGowen John A.
Published: April 2004

The cure behavior of epoxy resins in the presence of glass fillers was investigated using differential scanning calorimetry (DSC). A novel benzylsulfonium salt capable of covalently bonding to glass surfaces through a trialkoxysilane moiety were synthesized. Coupling of the salt to silica gel (as a model glass surface), characterization of the bound material, and its ability to initiate the cationic cure of DGEBA resins were investigated. The bound material was characterized by solid‐state 13C and 29Si CP/MAS NMR, FTIR, and TGA. The sulfonium salt was coupled with silica as the Br anion form because of the insolubility of the SbF6 salt. After anion exchange, silica‐bound salt with SbF6 counterion was shown to initiate cure of epoxy resins but only at temperatures much higher than with an analogous unbound salt (>200°C and <100°C, respectively). The inability to get complete anion exchange of Br anions for SbF6 (necessary for cationic initiation activity) after coupling allowed formation of excess tetrahydrothiophene (THT) during heating through decomposition of the residual Br salt, causing temporary termination and a large delay in cure. The temporary termination mechanism involved reaction of THT and the active oxonium ion to give a primary alkylsulfonium salt. In addition, it was discovered that the silica gel itself had an inhibiting effect on the cure of epoxy resins cured with unbound initiator, giving low Tg materials. This was due to inherent surface surface interaction with the salt and not to chemical reaction with the surface or with a physically adsorbed contaminant (such as water). The degree of inhibition increased with increasing filler content. Low surface area glass beads also inhibited cure, although surface modification of the glass beads with bound benzylsulfonium salt (SbF6 form) improved cure significantly, reducing onset delay and giving high Tg materials. The degree of delay was inversely dependent on the amount of silane coupled to the surface and varied with counterion.
Electrical properties of crosslinked polyethylene/carbon black switching composites as a function of morphology and structure of the carbon black
Authors: Yang Gengcheng , Teng Renrui , Xiao Peng
Published: April 2004

The electrical resistivity of a radiation‐crosslinked polyethylene/carbon black switching composite was investigated as a function of carbon black content and temperature. Carbon blacks of different morphology and microstructure behaved differently regarding the electrical resistivity. A HG black, highly porous and structured, imparts high conductivity to its composite mixture at a low degree of loading, whereas nonporous acetylene EQ black of like structure requires a higher degree of loading to impart the same conductivity. The PTC (positive temperature coefficient) effect anomaly was smaller for HG black than for EQ black. It was found that the PTC anomaly was heightened when a combination of the two different carbon blacks was mixed into the composites. Suggestions as to the causes for this particular behavior are made with reference to the electron micrography and other parameters for microstructure of the two carbon blacks.
Wholly thermoplastic composites from woven preforms based on nylon‐11 fibers reinforced in situ with a hydroquinone‐based liquid crystalline polyester
Authors: Krishnaswamy Rajendra K. , Baird Donald G.
Published: April 2004

This work concerns a novel means to generate wholly thermoplastic composites based on low‐melting thermoplastics reinforced with high‐melting thermotropic liquid crystalline polymers (TLCPs). A novel dual extrusion process was employed to generate nylon‐11 fibers that are reinforced with continuous fibrils of a hydroquinone‐based liquid crystalline polyester (DuPont TLCP, HX8000). These composite fibers display tensile properties significantly higher than those predicted by composite theory. These fibers were subsequently woven into a fabric, which in turn serves as a composite preform. Several layers of the fabric preform were stacked and consolidated to yield a composite plaque. The consolidation was carried out at temperatures just high enough for nylon‐11 to melt, but well below the melting temperature of HX8000. Fabric preform composites based on the composite fibers with ∼35 wt% HX8000 gave modulus values close to five and one half times that of nylon‐11, and strength values approximately two and one half times that of nylon‐11. The tensile and flexural properties of these composites are superior to continuous glass‐fiber reinforced composites at comparable loadings on a volume basis. Moreover, as the reinforcing fibrils are already encapsulated by the matrix, fiber wetting and fabric impregnation issues that are critical in the fabrication of continuous glass and carbon fiber composites are eliminated.