摘要:

AbstractThe usefulness of the transmission electron microscopy (TEM) technique in probing the morphology and toughening mechanisms of high performance composite systems is demonstrated. TEM provides an effective study of both the morphology and fracture behavior of graphite fiber reinforced epoxy and for cyanate composite systems. The failure process in these composites can be under stood. The TEM technique introduced here is found to be valuable for both fundamental and developmental research in improving both physical and mechanical properties of high performance composites. The present work focuses on demonstrating how a composite can be successfully prepared for TEM investigations. Experimental procedures concerning identification and isolation of the crack tip damage zoen, followed by cutting, trimming, staining, and thin section of the composite sample are detailed.

ISSN:0272-8397    

DOI:10.1002/pc.750150302

出版商:Society of Plastics Engineers    

年代:1994

数据来源: WILEY

摘要:

AbstractThis study critiques the use of both rubber particles and short‐glass fibers for the improvement of polymer fracture toughness (Kc). Although dry neat nylon is brittle with only a moderateKcvalue (4.2 Mpa√m), additions of either second phase produce risingKR‐curves and associated highKcvalues (8.1 Mpa√m for rubber‐toughened nylon, and 10.0Mpa√m for 17 vol% Glass‐fiber neat nylon). In the rubber ‐modified resin, the highKcvalue is associated with extensive plastic blunting at the crack tip. In the fiber‐reinforced neat resin,Kcis improved due to a combination of fiber‐bridging and increased strength, the latter being associated with additional load carrying capacity of the fibers. When both rubber and fibers are added, however, no further increase inKcis noted (Kc= 9.3 Mpa√m for 17 vol% glass‐fiber rubber‐modified nylon). The extent of ductile blunting in the rubber + fiber resin is not as great as in the rubber‐only resin. Furthermore, the fracure strength of the rubber + fiber resin is not as high as the fiber‐only resin. The net result is a balance of properties for t

ISSN:0272-8397    

DOI:10.1002/pc.750150303

出版商:Society of Plastics Engineers    

年代:1994

数据来源: WILEY

摘要:

AbstractA one‐dimensional devolatilization model is developed for autoclave processing of themroplastic polyimide, graphite‐reinforced, composites. The model rests on the assumption that continous gas passages are formed during processing due to partical crystallization of the polymer in the course of polymerization. Both DSC and optica microscopy indicate that crystallinity develops in the Avimid‐III polyimide resin during polymerization, which in turn facilitates formation of cracks. These cracks heal upon removal of volatiles and polymer melting. Model‐Calculated temperature profiles in the laminate during polymerization, and the predicted removal rates of volatile species (water, ethanol, NMP) are compared to experimental miniautoclave data for the DuPont Avimid K‐III/IM6 system. Good agreement is obtained when the volumetric mass transfer coefficient required by the model is assumed to vary proportionally to the inverse of the changing resin viscosity. The model allows the investigation of desired cure cycle parameters for different laminate th

ISSN:0272-8397    

DOI:10.1002/pc.750150304

出版商:Society of Plastics Engineers    

年代:1994

数据来源: WILEY

摘要:

AbstractProcessing Polycarbonate/carbon fiber composites for long times at high temperatures significantly improved adhesion between the matrix and the fibers. The interfacial properties were studied by measuring transverse fracture toughness, observing fracture specimens by scanning electron microscopy, and by monitoring composite cross‐sections using atomic force microscopy. The processing treatment provided an ideal method for varying the properties of the interface without changing any other properties. We used this method to study the effect of interfacial properties on the axial compression properties of unidirectional composites. Both the compression strength and compression modulus increased significantly as the fiber/matrix adhesion improved. We concluded that improving interfacial adhesion increased compression properties by inhibiting fiber microbucklin

ISSN:0272-8397    

DOI:10.1002/pc.750150305

出版商:Society of Plastics Engineers    

年代:1994

数据来源: WILEY

摘要:

AbstractThis study deals with the fracture process and acoustic emission (AE) characteristics of a randomly oriented E‐glass fiber mat reinforcement with a crosslinked polyester. These panels were evaluated after they were immersed in hot water. The fiber volume content of the panel was 19%. Glass fiber reinforced plastics (GFRP) panels wer immersed in water at 81°C. Bending and AE monitoring tests were Performed and after bending, the cross‐section of the specimen was observed by an optical microscope and SEM. The influence of degradation, due to water immersion, on the changes of fracture process of GFRP is discussed. The dominant fracture mode of the virgin specimen was matrix cracks, whereas that of the immersed specimen was debondings at the fiber bundle/matrix and fiber/matrix interfaces. This change was caused by reduction of the bonding strength at the interface. The scale of fracture can be estimated by both AE amplitude and AE energy and this estimation method was used to estimate the fracture mode changes of GFRP panels immersed in hot w

ISSN:0272-8397    

DOI:10.1002/pc.750150306

出版商:Society of Plastics Engineers    

年代:1994

数据来源: WILEY

摘要:

AbstractBased on an adhesive and fabric screening program, a rubber‐modified resole adhesive and a flexible grade plain weave glass fabric were found appropriate for the fabrication of a glass‐reinforced plastics honeycomb core material. Sandwich structures of different densities were fabricated. A linear regression analysis was performed to correlate the mechanical properties (S) with the density (p) for a wide range of sandwich structures based on honeycomb and cellular plastic core materials. An analytical model of the formS=Kρnwas derived, with two empirical constantsKandn. The density exponentnwas between 1 ≤n≤ 2 in all cases. An equation was also derived to relate density with thermal conductivity. The dynamic mechanical analysis (DMA) results revealed that the glass transition temperature of the resin matrix associated with the sandwich structure was higher than that of the corresponding facing laminate or near resin

ISSN:0272-8397    

DOI:10.1002/pc.750150307

出版商:Society of Plastics Engineers    

年代:1994

数据来源: WILEY

摘要:

AbstractA study of hygrothermal aging in terms of the kinetics of moisture absorption by nylon 6,6 and its carbon fiber reinforced composites has been carried out. The single free phase model of absorption has been applied to the kinetic data and thereafter the values of diffusivity have been evaluted. The diffusivity was found to be dependent on the conditioning temperatures and the volume fraction of fibers. Dynamic mechanical properties of unaged and aged samples were studied using a free resonance torsion pendulum which covers a temperature range of 350°C. Incorporation of carbon fibers has led to an increase in structural rigidity of the nylon 6,6 matrix especially at higher temperatures. This was reflected by the sharp increase in the relative shear modulus as the glass transition temperature of nylon 6,6 is appoached. Absorbed moisture was observed to plasticize the polymer matrix and decreased the temperatures of all the transitions. For instance, the α‐transition was shifted by almost 95°C. The intensities of the transition peaks of both unaged and aged samples were found to decrease with fiber volume fraction. Increasing the conditioning temperatures has resulted in a reduction of the shear storage modulus and this effect was found to be more pronounced in the reinforced nylon 6,6. This has been attributed to the increase in the extent of degradation at the fiber‐matrix int

ISSN:0272-8397    

DOI:10.1002/pc.750150308

出版商:Society of Plastics Engineers    

年代:1994

数据来源: WILEY

摘要:

AbstractThe use of dual beam microwaves to heat glass mat thermoplastic has been investigated numerically using a finite difference technique, known as the alternating difference implicit (ADI) method. The variation in thermophysical properties throughout the GMT has been accounted for using a table look‐up procedure, which provides the appropriate thermophysical properties for the thermal conditions at each mesh point. The use of dual beam microwaves has been shown to significantly reduce the heating times under all geometric conditions, material variations, and glass loadings. Sheet thicknesses were varied from 1 to 12 mm, glass loadings from zero to 40 wt% polypropylene, polycarbonate and nylon were all simulated. The computations indicate a clear advantage in heating times when dual beam microwave heating sources are emplye

ISSN:0272-8397    

DOI:10.1002/pc.750150309

出版商:Society of Plastics Engineers    

年代:1994

数据来源: WILEY

摘要:

AbstractThis paper presents a model using the self‐consistent method for estimating the resin flow permeability of fiber tow preforms. The permeable resin is assumed to be a Newtonian fluid, such as an uncured and low viscosity epoxy resin. Permeability in both longitudinal and transverse directions is considered. In the discussion, a basic cell insertion is constructed to include a representative fiber tow surrounded with fluid. The insertion is placed into a homogeneous medium with an unknown permeability. Stokes flow is applied to the fluid region, and Darcy flow is considered at the tow region and in the outside homogeneous medium. Boundary and interface conditions as well as consistent conditions, including the total amount of the flow and the dissipation energy, are applied accordingly. Permeability is solved from these considerations. The prediction expresions using parameters of average fiber volume fraction, tow volume fraction, and tow size are derived. The results show that the main flow paths are the openings or gaps between neighboring tows in both longitudinal and transverse directions. The observation provides a scientific base for the simplification of the problem treatmen

ISSN:0272-8397    

DOI:10.1002/pc.750150310

出版商:Society of Plastics Engineers    

年代:1994

数据来源: WILEY

摘要:

AbstractThe effect of plasma treatment duration on adhesion promotion of high modulus polyethylene fiber to a polyesterresin matrix has been studied. The adhesion level was evaluated using pull‐out tests. The relevant parameters are the average interface shear strength and the critical embedded length. Particular attention was paid to the sample preparation and testing procedure to minimize data scatter inherent to this method due in part to structural and surface defects of the fiber. The results demonstrate that adhesion is enhanced for plasma treatment times as short as 2 s, mostly because of chemical bonding. Interfacial shear resistance gradually increases for the longer times considered, up to 10 min. In the latter case, improvement may be due to fiber surface etching and roughening, rather than chemical bondin

ISSN:0272-8397    

DOI:10.1002/pc.750150311

出版商:Society of Plastics Engineers    

年代:1994

数据来源: WILEY