摘要:

AbstractThe flow behavior and fiber orientation in slit flow of a short fiber reinforced thermoplastic composite melt are investigated. A slit die with adjustable gap and interchangeable entrance geometries was designed and built. The slit die is fed by a single screw extruder. The bulk viscosity is calculated from the axial pressure profiles measured using three flush mounted pressure transducers. The effect of entrance geometry and gap dimensions on the fiber orientation and bulk flow behavior is specifically considered. A skin‐core composite fiber orientation is observed in the thickness direction. Fibers are oriented in the flow direction and parallel to the walls in the skin region irrespective of the entrance geometry. Different fiber orientation distributions in the core region can be realized by using different entrance geometries. However, the changes in the core fiber orientation are not fully reflected by the measured viscosities, due to highly oriented skin layer. Exit pressures obtained by extrapolation of linear pressure profiles are found to be all positive, but dependent on the die geometry and entrance conditions, even for the unfilled melt

ISSN:0272-8397    

DOI:10.1002/pc.750120302

出版商:Society of Plastics Engineers    

年代:1991

数据来源: WILEY

摘要:

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 orien

ISSN:0272-8397    

DOI:10.1002/pc.750120303

出版商:Society of Plastics Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractThe effect of60Co gamma radiation of up to 100 Mrads on an IM6‐G graphite fiber‐epoxy interface was studied using the single‐fiber‐composite (SFC) technique. Flexible epoxy blends were formulated using diglycidylether of bisphenol‐A (DGEBA) based and polyglycol diepoxide epoxies which were cured with aliphatic and aromatic curing agents. Bulk epoxy specimens and graphite fibers were tension tested to obtain their tensile properties. The fragment length distribution from SFC tests, single fiber strength data, and a Monte Carlo simulation of Poisson/Weibull model for fiber strength and flaws were used to obtain the effective interfacial shear strength values. The results indicate that while graphite fiber strength is not affected by radiation, the tensile properties of the epoxies used are adversely affected by the radiation. The interfacial shear strength, however, increases significantly with the radiation dose. The study also supports the earlier results of many workers that the interfacial shear strength for flexible epoxies is much higher than the shear yield strength of th

ISSN:0272-8397    

DOI:10.1002/pc.750120304

出版商:Society of Plastics Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractFibers can greatly improve the mechanical properties of polymers but may also severely weaken molded parts at their weld‐line compared to their bulk strength. The tensile properties and fiber orientation of injection and compression molded fiber reinforced Noryl and polypropylene samples with and without a weld‐zone were studied. Distinct differences in structure and mechanical properties of weld‐containing and weld‐free samples were identified. In unfilled Noryl and unfilled polypropylene, the presence of a weld‐line was found to only have a small effect on the tensile strength and modulus, while in the corresponding fiber reinforced systems, orientation of the fibrous reinforcement parallel to the weld‐line caused a significant reduction of the tensile strength compared to the weld‐free products. The strength ratio of welded and unwelded specimens was found to decrease with increasing fiber concentration. Quantitative determination of the glass fiber orientation distribution within the weld‐line region and in the bulk was carried out by analyzing photomicrographs of polished sections at de

ISSN:0272-8397    

DOI:10.1002/pc.750120305

出版商:Society of Plastics Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractCrystallization kinetics of short glass and carbon fiber composites of poly(ether ether ketone) (PEEK) under melt‐strain conditions have been obtained for the first time, usingin‐situwide angle X‐ray scattering, and have been correlated to a model based on the Avrami equation in order to enable minimization of the processing time for injection molding of these materials. It has been demonstrated that increased flow rate of the melt in the mold and, consequently, increased shear rate accelerates the crystallization process of PEEK composites, analogous to similar trends observed previously in PEEK resin. Short glass fiber composites of PEEK crystallize slower than the resin under identical processing conditions, while short carbon fiber composites crystallize faster than the resin, except at the highest mold temperatures and the lowest flow rates. A model based on the Avrami equation has been proposed to fit the kinetics data obtained experimentally. The Avrami coefficient has been calculated and Arrhenius plots have been used to predict the crystallization kinetics at temperatures lower than those at which experimental data have been obtained here. Fiber orientation, flexural elastic modulus, and flexural fracture toughness of the composites have also been eval

ISSN:0272-8397    

DOI:10.1002/pc.750120306

出版商:Society of Plastics Engineers    

年代:1991

数据来源: WILEY

摘要:

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 un

ISSN:0272-8397    

DOI:10.1002/pc.750120307

出版商:Society of Plastics Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractThe permeability characteristics of multilayer fiber networks generally differ from those of the constituent layers. In heterogeneous assemblies, the effective in‐plane permeabilities and flow anisotropies are governed by the high permeability layers or directions. Based on the observation that a transverse flow mechanism contributes to filling the low permeability layers, a semipermeable wall model has been constructed to analyze encroaching flows into multilayer systems. The model identifies three flow regimes: a region in which the layers act independently and are governed by single layer solutions, a region in which the layers act as a unified homogeneous system governed by the single layer solution with weighted average properties, and a region intermediate to these extremes. A comparison of model simulations and experimental data demonstrates that the model has good predictive capabilitie

ISSN:0272-8397    

DOI:10.1002/pc.750120308

出版商:Society of Plastics Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractElectrochemically initiated polymerization on carbon fibers is an attractive process for combining fibers with a polymer matrix. An aromatic monomer, α,α′‐para‐xylene, was successfully polymerized on carbon fibers in a three‐compartment electrolysis cell. A composite topreg with 40 volume percent of polymer was obtained. The polymer coating has a porous texture. The polymerization is rapid and efficient. Polymerization conditions and composite thermal properties are

ISSN:0272-8397    

DOI:10.1002/pc.750120309

出版商:Society of Plastics Engineers    

年代:1991

数据来源: WILEY

摘要:

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 geometrie

ISSN:0272-8397    

DOI:10.1002/pc.750120310

出版商:Society of Plastics Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractSamples of Narmco Rigidite 5208/WC3000 carbon‐epoxy composite prepreg were exposed to ambient temperature (22°C) and 50 percent relative humidity for different periods up to 66 days. The aging has a significant effect on prepreg physical properties such as tack, volatiles content, and gel time. A set of 4‐ply laminates made from aged prepreg was subjected to tensile testing, ultrasonic inspection, and optothermal inspection. No relationship could be discerned between laminate properties and prepreg aging time. However, variations in panel homogeneity were observed, and these correlated with thermal diffusivity and tensile modulus measurements, but not with ultimate tensile strength or elongation. A set of 6‐ply laminates was used to measure compressive properties, interlaminar shear strength, and physical properties. These panels also showed variations in porosity, again unrelated to aging, but in addition, the fiber/resin ratio was observed to decrease with aging time. Both factors were found to affect mechanical properties. The implications concerning the importance of monitoring the aging by physicochemical methods are dis

ISSN:0272-8397    

DOI:10.1002/pc.750120311

出版商:Society of Plastics Engineers    

年代:1991

数据来源: WILEY