摘要:

AbstractA three‐dimensionally woven fabric is proposed as a standard reference material for permeability characterization. The 3‐D woven fabric requires care in cutting and handling, although it is more robust than 2‐D woven or braided fabrics. If prepared carefully, the permeability of the 3‐D woven fabric can be measured reproducibly within 15% in either radial flow or saturated 1‐D flow geometries. The material was characterized for permeability in radial, unsaturated and saturated 1‐D, and through‐thickness flow geometries. The transient results demonstrated the importance of structural heterogeneity on the unsaturated flow behavior, and agree qualitatively with a simplistic model of flow in heterogeneous unsaturated porous media. The effects of heterogeneity were manifested in the proposed SRM by an increasing trend in the “unsaturated permeability.” Experiments were also conducted with a random mat that displayed transient flows dominated by wicking. The effects of wicking on the macroscopic flow behavior were manifested by transients in the “unsaturated permeability” in which a decreasi

ISSN:0272-8397    

DOI:10.1002/pc.750160602

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractWithin the resin transfer molding (RTM) process, flow is generally characterized by the progression of a distinct, nonuniform flow front into the preform as a function of time. The flow front progression introduces unsaturated characteristics into RTM flow fields. As a result, the definition of aneffectivein‐plane permeability (Keff) is used to determine the permeability of actual preforms as they fill with fluid. ThisKeffexpression expands upon the original definition of Darcy's law by generalizing its applicability tounsaturatedcreeping flows. Results of experimentally obtainedKefffor flow in single‐layer preforms have been detailed for two common RTM materials, a random mat and a 3‐D weave, in Part 1. In this paper (Part 2), we characterize the unsaturated and saturated permeabilities of multiple‐layer preforms constructed from the random mat and 3‐D weave materials characterized in Part 1. This work identifies the apparent permeability characteristics of a specific unsaturated multiple‐layer flow that demonstrates behavior inherent to this important class of heterogeneous flows. Also, parallels are drawn between the unsaturated permeability behavior of complex 3‐D weave materials and multiple

ISSN:0272-8397    

DOI:10.1002/pc.750160603

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractManufacture of thermoplastic composites is expensive because of the difficulty of impregnating the resin into the fibers. Powder processing shows great promise as an impregnation technique for cost‐effective manufacturing. This paper discusses an electrostatic powder spray impregnation technique that uses glass fibers. A geodesic fiber spreader is used to spread the fibers locally in the region of maximum powder deposition. A negative corona electrostatic spray gun is employed to charge and direct the powder for coating both sides of the spread fiber tow. The process has been used to impregnate glass fibers with poly(aryl ether ketone ketone) powder. The effect of the powder mass flow, corona voltage, and fiber tow velocity on powder deposition has been investigated. Particle image velocimetry is utilized to determine particle velocities. Compression molded panels have been produced and tested in three point bendin

ISSN:0272-8397    

DOI:10.1002/pc.750160604

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractThe resin transfer molding (RTM) technique often utilizes reinforcement with a complex fiber architecture. Several parameters, including the permeability tensor, are necessary to characterize the flow behavior in these intricate fibrous porous media. In this paper, a general procedure for extracting three‐dimensional permeability tensors from data is presented. A general procedure is warranted if the permeability tensor lies out of the material plane. An approximate solution to Darcy's law was employed to relate the components of the permeability tensor to experimental measurements. The procedure requires inverting six nonlinear equations with a robust binary search algorithm. The accuracy of the approximate solution to Darcy's law was checked and found to be in close agreement with a nearly exact solution to Darcy's law obtained by finite element method

ISSN:0272-8397    

DOI:10.1002/pc.750160605

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractThe degree of crystallinity in polymers is commonly known to significantly affect their mechanical properties. To that extent, it also affects the mechanical properties—such as compression, buckling, and creep—of thermoplastic composites that are matrix dominant. For this reason, it is important that the degree of crystallinity in a thermoplastic composite be precisely determined, which is the focus of this paper. In particular, the crystallinity for a thermoplastic poly(phenylene sulfide) composite reinforced with glass fibers is determined using an X‐ray diffraction technique (XRD). While conventional methods have been adopted for homogeneous phases, a modified method has been adopted to account for the heterogeneous nature of the composite. The results have also been compared with results obtained using DSC and DMA techniques, indicating that the XRD method yielded lower values, which are considered to be more accurate. This was attributed to the absence of a recrystallization effect in the XRD method, which was unavoidable in the other two me

ISSN:0272-8397    

DOI:10.1002/pc.750160606

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractA strategy involving the use of anionic surfactants to compatibilize titanium dioxide powders with nonpolar polymers has been applied to facilitate the dispersion of these powders into polymer composites. The methodology first involves the adsorption of surfactant onto the powder within aqueous dispersions. Surfactantcoated powders are then removed from the dispersion and dried. The cohesivity and some surface properties of the surfactant‐coated powders were measured and compared to that of the uncoated powders. Dispersion experiments of titania agglomerates in polyethylene were performed in a rotating cone‐and‐plate device set within a temperature controlled oven. The titania agglomerates dispersed by an erosion mechanism in which small fragments detached from the surface of the parent agglomerate. The erosion rate was higher for the surfactant treated powders in comparison to uncoated powders. The links between the enhanced erosion rates and the surfactant coating were investigated in terms of the cohesivity of the powders, the penetration of the polymer into the agglomerates, and the interactions between the powders and the polymer media that govern wetting and the transmission of hydrodynamic s

ISSN:0272-8397    

DOI:10.1002/pc.750160607

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractThis investigation focuses on the effects of thermal dispersion in resin transfer molding (RTM). A set of volume‐average balance equations suitable for modeling mold filling in RTM is described and implemented in a numerical mold filling simulation. The energy equation is based on the assumption of local thermal equilibrium and includes a dispersion term. Thermal dispersion is an enhanced transport of heat due to local fluctuations in the fluid velocity and temperature away from their average values. Nonisothermal mold filling experiments are performed on a center‐gated disk mold to investigate and quantify dispersion effects. Good agreement is found between the experimentally measured and numerically predicted temperatures, and a function for the transverse dispersion coefficient in a random glass fiber mat is determined. The results indicate that thermal dispersion is important in RTM processes and must be included in simulations to obtain accurate predicti

ISSN:0272-8397    

DOI:10.1002/pc.750160608

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractSamples of 16‐ply, quasi‐isotropic bismaleimide composites were aged in convection ovens at 150°C, 177°C, and 204°C for up to 16,000 hours. As a measure of degradation, transverse microcrack density was characterized as a function of time, temperature, and ply depth. Times required to reach onset and saturation crack density were delayed on the tool side of the laminate, for lower temperatures, and for deeper ply depths. Saturation crack densities ranged from 35 cracks/cm to 46 cracks/cm, depending on ply depth. Master curves were constructed for each ply level to express all time‐temperature data for that ply as a single reference curve. A mass transfer analysis further suggests that diffusion is the controlling mechanism in the degradation process. Finally, a prediction of the degradation behavior in the 120,000‐h lifetime of the HSCT aircraft for a sustained temperature of 150°C indicates that ∼13 plies will have reached initiation in a quasi‐iso

ISSN:0272-8397    

DOI:10.1002/pc.750160609

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractEnvironmental behavior of reinforced polyester was studied by stress relaxation. Relaxation failure of polyester matrix and fiberglass degradation appear dramatically at short time after exposure to acid and alkali electrolytes. The relaxation spectrum is thus influenced by environmental action. Indeed, the stress relaxation modulus is a sensitive characterization of environmental effects.

ISSN:0272-8397    

DOI:10.1002/pc.750160610

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractTwo‐dimensional (2D) carbon/carbon composites were prepared with phenol‐formaldehyde resin and a commercial stabilized PAN fabric. The effect of pyrolysis on the microstructure and flexural strength of the composites during the carbonization process was studied. The interaction between fabric and matrix inhibited the decomposition and the thermal fragmentation, leading to a higher carbon yield for the final composition. Because of the formation of strong bonding in the fiber/matrix interface, the composites made with stabilized PAN fabric showed catastrophic failure and low flexural strength below carbonization temperatures of 600°C. Above 600°C, the flexural strength of the composites increased with the increase in the carbonization temperatures, even when the fracture behavior showed catastrophic fa

ISSN:0272-8397    

DOI:10.1002/pc.750160611

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY