摘要:

AbstractInterlayers of controlled composition and thickness were applied to commercial graphite fiber bundles by electrochemical copolymerization, and the impact and interlaminar shear strength of composites from these coated fibers were examined. Glycidyl acrylate/methyl acrylate copolymers represented coatings that were reactive to the epoxy matrix during curing; acrylonitrile/methyl acrylate copolymers represented non‐reactive systems. The reactive systems showed 10 to 30 percent simultaneous improvement in impact and interlaminar shear strengths, while the non‐reactive system failed at the interlayer‐epoxy interface and showed no improvement. There is an optimum interlayer thickness of 0.1 to 0.15 micron; the possible reasons are discussed. A detailed scanning electron microscope study illustrates how the structure of the composite fracture surface varies with the systematic changes in interlayer reactivity, composition, and thickness. Determination of the locus of failure is discussed. The observations are consistent with the mechanical property measure

ISSN:0272-8397    

DOI:10.1002/pc.750120402

出版商:Society of Plastics Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractSuspensions filled close to their maximum packing fraction present special challenges in their processing and in their rheological characterization. In this report, the literature in the area of dilatancy of concentrated suspensions is reviewed. Furthermore, the shear viscosity of a Newtonian polymeric liquid filled with 60 vol. percent of ammonium sulfate has been investigated. Both capillary and parallel disk torsional flows, were employed, spanning three decades in shear stress. Upon correction for slip, the suspension exhibited shear thinning at low shear stresses and shear thickening at higher shear stresses. Above a critical wall shear stress, the shear viscosity of the suspension increased unboundedly and the flow became pluglike with apparent slip at the wall. These findings have important ramifications in the processing of composites from such concentrated suspensions.

ISSN:0272-8397    

DOI:10.1002/pc.750120403

出版商:Society of Plastics Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractThis paper demonstrates the usefulness of careful experimental work with model composite materials, such as thin polymeric films in which single fibers are accurately positioned, in at least two respects: to assess the validity of a theory for a given physical property, and to accurately probe the effects of various parameters on the behavior of composites. Working with such model composites has obvious advantages, such as the full control of experimental parameters, the possibility of introducing perturbative effectsin a controlled way, and the possibility of verifying theoretical models in the range of low fiber content. Indeed, macroscopic composite materials contain various types of defects and perturbative effects, such as fiber misalignment or slack, fiber‐poor regions, voids, etc., which bias any quantitative assessment of mechanical and physical properties, and preclude the accurate verification of theoretical schemes. One difficulty in working with microcomposite models, also recalled here, is the need for an appropriate “scaling‐up” procedure to the level of macroscopic com

ISSN:0272-8397    

DOI:10.1002/pc.750120404

出版商:Society of Plastics Engineers    

年代:1991

数据来源: WILEY

摘要:

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 com

ISSN:0272-8397    

DOI:10.1002/pc.750120405

出版商:Society of Plastics Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractA literature survey is presented on sheet‐forming methods and mechanisms for continuous fiber reinforced thermoplastics. The diaphragm forming process is shown to be one of the more promising fabrication routes for complex‐curvature structures. The primary deformation mechanisms involved in the sheet‐forming processes are identified and discussed. Earlier approaches to develop mathematical models either have been kinematically based or have treated only one of the primary deformation mechanisms. A promising constitutive model for the highly anisotropic behavior of the composite at forming temperature is examined. The composite sheet is assumed to behave as a transversely isotropic Newtonian fluid that is both incompressible and inextensible in the fiber direction. The second section of the paper treats the experimental development of the polymeric diaphragm forming process for thermoplastic composites. The viscoelastic properties of the diaphragm material are characterized by dynamic mechanical analysis. The rate sensitivity of the phenomenon of shear‐buckling during forming of certain cross‐ply and quasi‐isotropic composite laminates is investigated, using a shallow female mold. Finally, the interface condition between the diaphragm and the composite during forming

ISSN:0272-8397    

DOI:10.1002/pc.750120406

出版商:Society of Plastics Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractThermoforming has been studied for a single curvature part made from various advanced thermoplastic matrix composite prepregs. For parts with acceptable shape conformity, preheating of the composite laminates to a processing temperature of 350 to 400°C is necessary prior to forming with molds maintained at 200°C. However, only PEEK/carbon fiber prepreg tapes yielded parts with acceptable microstructural integrity and a matrix crystallinity level of about 30 percent. Amorphous matrix based PXM 8505/T500 fabric prepregs also result in lamination and void free parts, but fiber matrix distribution in this case was rather poor. Parts thermoformed from other prepreg laminates contained voids and/or were delaminated, thereby indicating the need for higher mold temperature and forming pressure than that afforded by the present study, in which a standard lab‐scale thermoforming machine was u

ISSN:0272-8397    

DOI:10.1002/pc.750120407

出版商:Society of Plastics Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractDynamic mechanical analysis, stress relaxation, and creep experiments were performed to characterize the viscoelastic properties of a basic unmodified epoxy (Hercules 3501‐6) and a modified multiphase epoxy (Hercules 8551‐7), which are commonly used as matrices in high performance composites. The Arrhenius and WLF equations and a modified Standard Linear Solid (SLS) Model were used to quantify the viscoelastic behavior below, above, and at the glass transition temperatures, Tg. Both the modified and the unmodified epoxy systems exhibited a single relaxation peak above ambient temperature. TheTgof the modified epoxy at full cure was 170°C, which is 50°C lower than that of the basic epoxy. The glassy moduli of these two resin systems were found to be comparable, but the rubbery modulus of the modified epoxy was much lower than that of the basic epoxy system. However, the viscoelastic behavior of these two systems and their sensitivity to time‐temperature may be considered to be quite similar if they are compared with respect to their corresponding glass transition tempe

ISSN:0272-8397    

DOI:10.1002/pc.750120408

出版商:Society of Plastics Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractInterfacial adhesion between graphite fibers and epoxy matrices is one of the important parameters in controlling composite performance. Experiments were performed to verify the idea that polymerizable and nonpolymerizable nonionic surfactants can promote wetting and increase interfacial shear strength. Using a single‐fiber‐composite (SFC) technique with a Poisson/Weibull model of fiber strength and flaws, the effective interfacial shear strength (ISS) was determined. The effect of surfactant treatments on interfacial adhesion in single graphite/epoxy composites was also compared with the effects of treatment with deionized water, absolute alcohol, and acetone. The experimental results showed that the fibers treated with the nonpolymerizable surfactant gained 37% in interfacial shear strength relative to those untreated or those treated with deionized water, absolute alcohol, or acetone. The polymerizable surfactants showed a 10% increase in interfacial shear strength. The lognormal distribution provided the best fit for critical aspect ratios obtained from the SFC te

ISSN:0272-8397    

DOI:10.1002/pc.750120409

出版商:Society of Plastics Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractA lightweight conducting polymer composite was prepared by the incorporation of conducting polypyrrole in the pores of a host polymer to form a conductive network. The inclusion of polypyrrole in a porous cross‐linked polystyrene host polymer, prepared by the concentrated emulsion polymerization method, was carried out by imbibing the host polymer with a pyrrole solution (or oxidant solution), partially drying the saturated host polymer, and imbibing it again with the oxidant solution (or pyrrole solution) for 2 h. The conductivity of the polymer composite is as high as 0.5 S/cm and the shielding effectiveness of the composite reaches 26 dB in the frequency range from 1.0 to 2.0 GH

ISSN:0272-8397    

DOI:10.1002/pc.750120410

出版商:Society of Plastics Engineers    

年代:1991

数据来源: WILEY

ISSN:0272-8397    

DOI:10.1002/pc.750120401

出版商:Society of Plastics Engineers    

年代:1991

数据来源: WILEY