bluuebunny/crossref_metadata_2025_split huggingface dataset:
The occurrence of surface roughness in gas assist injection molded nylon composites
Authors: Liu Shih‐Jung , Chang Jer‐Haur 
Published: April 2004

AbstractGas 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

AbstractTo 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

AbstractBond 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

AbstractThe 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

AbstractFor 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

AbstractThe 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

AbstractDC 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

AbstractAn 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

AbstractThe 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

AbstractLignin, 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

AbstractThis 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

AbstractThe 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

AbstractThe 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

AbstractThis 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

AbstractNotch 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

AbstractAn 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

AbstractLow‐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

AbstractThe 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

AbstractThe 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

AbstractThis 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.
Environmental effects on the static strength and stress relaxation of a quartz fabric–reinforced, cyanate resin–matrix composite
Authors: Gutman E. M. , Grinberg A. , Ribak E. A. , Petronius I. 
Published: April 2004

AbstractEnvironmental effects are an important consideration when one is designing polymer matrix composites (PMC). The mechanical behavior of a quartz fabric–reinforced, cyanate resin–matrix composite was studied by tensile tests, compression tests, and stress relaxation tests. Compression and tensile strength as well as smaller relaxation spectra were obtained after exposing the material to different environments involving printed wire board (PWB) in aviation systems: Skydrol hydraulic oil (25°C), salt spray (5% NaCl at 95°F), alkaline solution (45 g/l 50°C), and nitric acid (304 g/l 25°C). Although only a small amount of environmental liquid was absorbed, it nonetheless had an acute effect on the mechanical properties and lifetime of the material.