bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractA 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

AbstractThis 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

AbstractThe 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

AbstractThe 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

AbstractPhoto‐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

AbstractThis 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

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

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

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

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

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

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

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

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

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

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

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