bluuebunny/crossref_metadata_2025_split huggingface dataset:
The silane interphase of composites: Effects of process conditions on γ‐aminopropyltriethoxysilane
Authors: Culler S. R. , Ishida H. , Koenig J. L. 
Published: December 2004

AbstractFT‐IR spectroscopy was used to collect spectra of γ‐aminopropyltriethoxy silane (γ‐APS) coupling agent deposited on KBr plates, modeling the silane interphase of composites, to study the effects of heating the γ‐APS film under various environmental conditions. This coupling agent is used in fiber‐reinforced epoxy composites. An aminebicarbonate salt forms when the sample is dried in a moist carbon dioxide environment giving rise to a series of bands from 2800 to 2000 centimeter−1 (cm−1) and bands at 1637 cm−1, 1330 cm−1, 696 cm−1, and 663 cm−1. The primary amine group is split into two bands at 1572 cm−1 and 1486 cm−1 in the NH3+ form. Heating removes the aminebicarbonate salt at temperatures above 95°C and condenses the γ‐APS polymer to a polysilsesquioxane film. The aminebicarbonate salt partially reforms if the γ‐APS film is stored in a moist CO2 environment. At temperatures above 120°C the primary amine of γ‐APS is oxidized in air to imine groups. In the process of evolving the CO2 the polymer is further condensed and the amine groups can be converted to imines if the temperatures exceeds 120°C. Both processes reduce the reactivity of the coupling agent with the epoxy resin. The structure of the silane interphase must be controlled during the processing of the composite to yield materials with maximum properties.
The effect of fiber‐matrix stress transfer on the strength of fiber‐reinforced composite materials
Authors: Dilandro L. , Dibenedetto A. T. , Groeger J. 
Published: December 2004

AbstractA model for the mechanism of tensile failure in oriented fiber composites based on random fragmentation of the reinforcing fibers biased by stress concentrations at fracture sites has been developed. Single‐fiber composites and composite strands of 34 to 36 volume percent fiber were prepared from an epoxy resin reinforced with Hercules AS4, HMS4, and IM6G carbon fibers. Fiber strength distributions and single‐fiber composite fragmentation data were used to calculate theoretical composite tensile strengths, which were then compared with experimental values. The fractures in single‐fiber composites were observed in situ under cross‐polarized light, and the mechanisms of interfacial failure were discussed.
Review of methods for characterization of interfacial fiber‐matrix interactions
Authors: Narkis M. , Chen E. J. H. , Pipes R. B. 
Published: December 2004

AbstractThis paper reviews various common methods for studying fiber‐matrix interaction with specific evaluation of the critical fiber length method. Commonly accepted methods are often shown to be unsatisfactory because interfacial results may not be independent of fiber tensile strength properties. A new concept for measuring fiber‐matrix interaction in a single filament, or in a single uniaxially reinforced thin layer, sandwiched between two relatively thick unreinforced layers is proposed. This method relies upon variable curvature bending jigs introducing continuously changing longitudinal shear profiles across the fiber surface by clamping the sandwiched specimen onto the jig surface and also upon the availability of physical detection methods of debonding fronts.
Some studies on glass fiber‐reinforced polypropylene. Part I: Reduction in fiber length during processing
Authors: Gupta V. B. , Mittal R. K. , Sharma P. K. , Mennig G. , Wolters J. 
Published: December 2004

AbstractThe reduction in fiber length during extrusion and injection molding of two commercial glass fiber‐reinforced polypropylene products containing 30 percent by weight of glass fibers was studied. The first product had very small fibers of average length around 0.5 mm and also contained a coupling agent. The second product contained relatively longer glass fibers of 9 mm length and no coupling agent. In both cases, fiber attrition occurs predominantly at the solid‐melt interface in the meiting zone of the extruder. However, in the short fiber granules, the maximum of the length distribution, which for the initial sample is around 0.5 mm, moved to shorter fiber lengths along the screw channels further from the hopper. In the long fiber granules, a bimodal length distribution was obtained in the intermediate channels; the first maximum was around the original length of 9 mm and the second centered around 0.5 mm. Thus, the forces at the solid‐melt interface result in fiber breakage to lengths which are predominantly around 0.5 mm. The fiber attrition was observed to be more severe in injection molding apparently because of higher shear rates and also because the fibers had to pass through narrow channels. The measured distributions of fiber length along the screw channels for the two products are presented, and the possible mechanisms of fiber breakage are discussed. The mechanical properties of samples containing different fiber length distributions and the effects of fiber length and interfacial adhesion on properties are presented and discussed in Part II.
Mat formation and unstable flows of highly filled suspensions in capillaries and continuous processors
Authors: Yilmazer Ulku , Gogos Costas G. , Kalyon Dilhan M. 
Published: December 2004

AbstractSuspensions, which are filled at loading levels approaching their maximum packing fractions, present special processing challenges. The flow and deformation behavior of such highly filled suspensions are dominated by strong slip effects. Furthermore, during pressure driven flows of these suspensions, the polymer matrix can filter out, giving rise to demixing and unstable flows. In this study, the capillary flow and extrusion of highly filled suspensions of ammonium sulfate and other salt fillers in a poly(butadiene acrylonitrile acrylic acid), PBAN matrix were investigated. The experimentally observed instabilities were elucidated in conjunction with a proposed mechanism, involving slip and filtration rates. This mechanism suggested greater affinity to unstable flows with relatively lower matrix shear viscosity, greater particle size of the filler, and greater convergence ratio; all of which were experimentally verified.
Characterization of the fracture toughness property (G1c) of composite laminates using the double cantilever beam specimen
Authors: Lee S. , Gaudert P. C. , Dainty R. C. , Scott R. F. 
Published: December 2004

AbstractThe results of a study on the interlaminar fracture toughness properties (G1c) of four unidirectional carbon fiber epoxy materials are presented. The selected materials included Narmco 5245C, Hexcel F584, and American Cyanamid 1806 resins reinforced with Hercules IM6 fibers and for a baseline material Narmco 5208 reinforced with T300 fibers. TheG1cvalues determined on Double Cantilever Beam specimens were found to range from 93 to 370 J/m2. The higher values may partly result from fiber bridging during fracture. This paper discusses specimen configuration, test procedure, and the Scanning Electron Microscope results.
Tensile properties of injection molded long fiber thermoplastic composites
Authors: Denault J. , Vu‐Khanh T. , Foster B. 
Published: December 2004

AbstractThis paper deals with the mechanical performances of a new class of injection molded long fiber composites based on PP and PBT matrices. Effects of material parameters such as fiber concentration, breakage, orientation, and matrix composition are analyzed. The critical fiber length, l, of the PP long fiber composite, evaluated from the pull‐out length of the tensile fracture surface, was found to be much higher than those previously reported. Tensile strength calculated from the measured ll and fiber length distribution in the molded samples was found to be in agreement with the measured values. From this work it is concluded that higher mechanical performances of the long fiber reinforced thermoplastics will be attained by the injection molding process to further reduce fiber breakage.
The prediction of flow and orientation behavior of short fiber reinforced melts in simple flow systems
Authors: Kamal M. R. , Mutel A. T. 
Published: December 2004

AbstractA model for the prediction of changes in fiber orientation in simple flows of fiber suspensions is proposed. Fiber interactions are modeled as randomizing forces over the rotation of fibers in closed orbits in simple shear. The resulting Fokker‐Planck type convection‐diffusion equation in orientation space is solved using a finite difference technique. The solution technique permits the use of periodic boundary condition for the convection‐diffusion equation and different initial conditions for the orientation distribution. The model predictions for simple shear flow demonstrate the interaction between the structural changes and the bulk rheological properties. The effect of non‐Newtonian fluid properties on the orientation distribution was also incorporated at the slow flow limit. Structural changes are assumed to be irreversible. The irreversibility is incorporated through an orientation distribution dependent diffusion coefficient.
Injection molding of glass flake reinforced polypropylene: Flake orientation and stiffness
Authors: Bouti A. , Vu‐Khanh T. , Fisa B. 
Published: December 2004

AbstractThree samples of silane treated glass flakes of different diameters were dry blended with polypropylene powder and injection molded into rectangular (32 mm × 127 mm) plaques using an edge‐gated mold cavity. The thicknesses of plaques were 1.6 mm, 3.2 mm, and 6.4 mm. Tensile and flexural specimens were machined from these plaques. Average flake diameters and thicknesses were determined. It was found that aspect ratios in finished moldings are quite similar, despite the initial (before processing) differences. The flake orientation varies across the thickness; it is parallel to the plane of the molding in the outer skin layer, changing gradually to perpendicular in the core. The relative thickness of the skin where the flake orientation is parallel increases with the decreasing thickness and flake concentration. It represents about 85% of the overall thickness in 1.6 mm moldings, between 70% and 85% when the plaque thickness is 3.2 mm, and between 50% and 60% in the thickest (6.4 mm) molding. Elastic properties can be interpreted using the modified rule of mixtures. Tensile moduli depends strongly on the flake orientation in the core and on the flake concentration, whereas the influence of the core on flexural moduli is insignificant. The flake orientation coefficients determined from micrographs are in good agreement with those calcuated from mechanical test. The coefficient accounting for finite flake aspect ratio, ηL was found to be about 0.3.
Crystallization of poly(aryl‐ether‐ether‐ketone): Effect of thermal history of the melt on crystallization kinetics
Authors: Deslandes Y. , Day M. , Sabir N.‐F. , Suprunchuk T. 
Published: December 2004

AbstractDifferential Scanning Calorimetry (DSC) and optical microscopy were used to investigate the effect of the thermal history of the melt on the crystallization of a commercial sample of poly(aryl‐ether‐ether‐ketone) (PEEK). Heating a film of PEEK at a temperature above the melt temperature for various periods of time changes the nucleation and crystal growth rate upon cooling the sample. Destruction of existing nuclei, formation of new nuclei, chain branching, cross linking, and chemical degradation of the macromolecular chains are all believed to take place at different times and to different extents during the thermal melt processing of the polymer. This study suggests that the thermal history of the melt plays an important role in the crystallization of PEEK samples.
Processing and characterization of new bismaleimide matrix advanced composites
Authors: Viot J.‐F. , Giraud Y. , Camberlin Y. , Lopez P. , Meissonnier J. 
Published: December 2004

AbstractBismaleimide polymers offer a thermostability that fills in the gap between epoxies and high temperature polyimides. Bismaleimides of the new generation overcome traditional problems of brittleness and difficult processing. The property transpositions from these tougher, hot‐melt processable resins to the corresponding carbond fiber composites are detailed, focusing on crack propagation behavior. Particularly, the mode I critical strain energy release rate (GIC) is compared to the mode I interlaminarGICof the corresponding composites (both unidirectional and woven laminates). Parameters of the transposition are tried to be identified.
Simultaneous measurements of permeability and capillary pressure of thermosetting matrices in woven fabric reinforcements
Authors: Ahn K. J. , Seferis J. C. , Berg J. C. 
Published: December 2004

AbstractA simple apparatus was designed and constructed capable of measuring the unsteady‐state permeability and the capillary pressure simultaneously in a simulated composite impregnation experiment. It was found that the Kozeny‐Carman equation used to describe the permeability of composites during impregnation adequately described experimental results for woven fabric preform up to porosity values of 0.5. Above this value, observed deviations were attributed to interfacial effects between adjacent woven fabric layers. For woven fabric preforms made of T‐300 carbon fibers, a maximum capillary pressure of 3.7 × 104Pa (=5.4 psi) was observed at low porosity values. Thus, the capillary pressure may compete with other pressure sources in low pressure processes, such as the prepregging process. The woven fabric preform used in this study is observed to have a permeability similar to a unidirectional fibrous preform along the transverse direction. Furthermore, an existing modeling methodology capable of predicting permeability and capillary pressure through different preforms was found to be valid for fibrous preforms of complex orientation.
Permeability characteristics of multilayer fiber reinforcements. Part I: Experimental observations
Authors: Adams Kurt L. , Rebenfeld Ludwig 
Published: December 2004

AbstractThe fluid permeability characteristics of homogeneous and heterogeneous multilayer fabric assemblies were determined by a radial in‐plane flow technique. The permeabilities and flow anisotropies of multilayer assemblies generally differ from those of the constituent layers. In homogeneous assemblies, the creation of interlaminar pores can increase the effective in‐plane permeability. In heterogeneous assemblies, the effective in‐plane permeabilities and anisotropies are governed by the high permeability layers or directions. A transverse flow mechanism contributes to filling the low permeability layers and keeping the fluid front macroscopically uniform.
Ballistic response of polymer composites
Authors: Zee R. H. , Wang C. J. , Mount A. , Jang B. Z. , Hsieh C. Y. 
Published: December 2004

AbstractA new microvelocity sensor unit was developed to measure the instantaneous velocity of a projectile during the penetration process. The concept of this device is based on the induced current generated in a coil resulting from the passage of a magnet. A special digital circuit was designed to yield a spatial resolution of better than 2.5 mm by elimiating the problem of signal overlap. The time delays obtained from these signals were used to determine the slowing down or energy loss of a high velocity projectile. A light gas gun was used to propel aluminum projectiles to velocities up to 320 m/s. Energy loss of these high velocity projectiles in composites reinforced with polyethylene, polyester, and graphite fabrics was investigated. Two distinct energy loss mechanisms were detected, one due to the actual fracture process and the other to the generation of frictional heat. Extensive delamination was observed in the more ductile PE and PET composites, but not in graphite. Low velocity instrumented drop‐tower impact tests were also conducted, using identical specimens and similar impact geometries.
A study of damage accumulation in unidirectional glass reinforced composites via acoustic emission monitoring
Authors: Kander R. G. 
Published: December 2004

AbstractDamage accumulation in continuous unidirectional glass reinforced composites was studied by acoustic emission (AE) monitoring during three‐point‐bend loading. Results are presented for four composites monitored during quasi‐static break loading, and one composite also monitored during cyclic fatigue and static creep loading. AE response was correlated with the mechanical (stress‐strain) response and with visual observation of damage events to study the details of the damage accumulation process. Results show that the failure process is characterized by the sequential occurrence of three distinct damage mechanisms. Specifically, the failure process initiated with cohesive matrix damage, propagated with interfacial debonding, and ended with fiber breakage very near catastrophic failure. The same sequential damage process occurred in all four composites and all three test procedures examined. Results also demonstrate that AE analysis, in combination with mechanical testing and microscopic observation, is a valuable tool in understanding damage accumulation in composites.
Application of the J‐integral concept for the description of toughness properties of fiber reinforced polyethylene composites
Authors: Grellmann Wolfgang , Seidler Sabine , Lauke Bernd 
Published: December 2004

AbstractFor the determination of toughness properties of HDPE/glass fiber and HDPE/cotton fiber composites, an instrumented Charpy impact test has been used. The interpretation of impact load‐deflection curves has been carried out with several concepts of fracture mechanics. Here the limits of linear elastic fracture mechanic (LEFM) have been shown. The change of toughness properties with increasing fiber volume can be described for short fiber reinforced composites with the help of the J‐integral concept in a suitable mode. An application of the conventional Charpy impact test will result in an overestimation of material behavior because of the energy of crack propagation. With the help of a micromechanical model to describe failure processes, taking account of energy dissipative processes, it is possible to calculate fracture mechanical material parameters. Because of the peculiarities of deformation and fracture behavior, the application of elastic‐plastic fracture mechanic (EPFM)‐concepts for fiber reinforced polymers is required.
The failure morphology of PEEK/carbon fiber ±45° angle‐ply laminates
Authors: Burnett P. J. , Cervenka A. 
Published: December 2004

AbstractThe ultimate strength of certain thermoplastic matrix laminates is observed to be strongly dependent upon the stacking sequence. Such effects are thought to be due to the development and action of through‐thickness stresses at the edges of laminates. However, the action of such stresses is not normally considered in Classical Laminate Theory. This paper describes experimental studies of the development of damage in, and subsequent failure of, a family of laminates that exhibit “through‐thickness” effects. Important differences between the mode of failure and development of damage prior to failure are identified, and these observations correlated with other workers' predictions concerning the presence and actions of edge stresses.
Thermally stimulated current in glass‐laminated unsaturated polyester resins
Authors: Jelčič Ž. , Ranogajec F. , Babić L. , Ivanović Z. 
Published: December 2004

AbstractExperimental results are reported on the electrical properties of glass‐laminated unsaturated polyester (UP) resins. Measurements of the poling current as a function of temperature reveal two different activated processes. Above 50°C the activation energy is 160 kJ/mol and has been associated with ionic condition, possibly by protons, while at lower temperatures (below −70°C) the activation energy is very low (less than 40 kJ/mol) and is associated with dipole relaxation. It is concluded that the laminated UP resin undergoes a phase transformation between low and high temperatures, which gives rise to a completely different electrical response. This phase transformation can be associated with the glass transition of UP resin phase. In view of the low activation energy, giving rise to a polarization peak, it is concluded that the low temperature range (glassy state) favors strictly localized motions of charges—most likely electrons. At higher temperatures, the behavior corresponds to d.c. conductivity and is associated with extended motions of charge carriers with limitations at contacts and at internal barriers. According to the air gap measurements, the pronounced dip found in the temperature dependence of the poling current (in the range from 20 to −30°C) may be due to separation of conduction and dipole relaxation current. Thermally stimulated depolarization (TSD) current measurements reveal the presence of high internal fields due to space charges accumulated at the phase boundaries of glass fibers.
Flow simulation in molds with preplaced fiber mats
Authors: Young W. B. , Fong K. Han. L. H. , Lee L. James 
Published: December 2004

AbstractThe primary goal of this study was to develop 2‐D and 3‐D computer simulation schemes for the mold filling processes of structural reaction injection molding (SRIM) and resin transfer molding (RTM) under isothermal conditions. The developed computer code was able to simulate the mold filling in molds with complicated geometry, Experiments were also carried out based on flow vitalizations. Experimental results were compared with the numerical simulations.
The consolidation of commingled thermoplastic fabrics
Authors: Van West B. P. , Pipes R. Byron , Advani S. G. 
Published: December 2004

AbstractCommingled fabrics composed of yarns containing both the reinforcement and the matrix in fiber form are an innovative preform for thermoplastic composite materials. The material is consolidated into a rigid structure by the application of heat and pressure. A mathematical model of the consolidation process for commingled fabrics has been developed. The model predicts the variation of laminate thickness, fiber volume fraction, and void content during the consolidation process as well as the time required to reach full consolidation. Materials composed of initially separate, commingled or cowoven fiber bundles are considered. The influence of fiber velocity induced by compaction on the flow of matrix is accounted for. An equivalence factor has been derived so that a one‐dimensional flow analysis may be used to model the impregnation of elliptical bundles of varying aspect ratio. This permits an analytic solution to the governing equation for fiber bundle impregnation. The model was utilized to examine the influence of various material and processing parameters on consolidation behavior.
Elastic moduli and thermal conductivity of injection‐molded short‐fiber–reinforced thermoplastics
Authors: Choy C. L. , Leung W. P. , Kowk K. W. , Lau Felix P. 
Published: December 2004

AbstractThe nine independent stiffness constants of injection‐molded tensile bars of poly(phenylene sulfide) reinforced with 30 and 40% by weight of carbon or glass fibers have been measured by ultrasonic techniques. The thermal conductivities along the three principal directions of these thermoplastic composites have also been determined by the laser‐flash radiometry method. The elastic moduli (tensile and shear) and thermal conductivity increase with increasing fiber volume fraction,vf, with the tensile modulus and thermal conductivity along the mold flow direction showing the greatest change. For a composite, containing 40 weight % of carbon fibers, the Young's modulus and thermal conductivity along this direction exceed those of the polymer matrix by a factor of 8. Using the known values ofvfand the observed aspect ratio and orientation factor of the fibers, the elastic moduli and thermal conductivity have been calculated on the basis of the laminate theory. The agreement between theoretical predictions and experimental data is better than 10% on the average.