摘要:

AbstractTin‐lead (60Sn‐40Pb) flake poly(ether sulfone) (PES) composites in which the flakes were partially interconnected and of average thickness 2 μm were prepared by hot pressing molten Sn‐Pb particles in a matrix of PES at a temperature above the melting temperature of Sn‐Pb and above the glass transition temperature of PES. Hot pressing at 240°C and 6.51 Mpa resulted in a 15 vol% Sn‐Pb composite of lower electrical resistivity and higher electromagnetic interference shielding effectiveness than a PES composite containing 15 vol% aluminum flakes that were not formedin‐situ.The electrical properties of thein‐situPES/Sn‐Pb flake composites were much better than those of PES/Sn‐Pb flake composites were fabricated by hot pressing at 310°C (the manufacturer‐suggested fabrication temperature), though the mechanical prope

ISSN:0272-8397    

DOI:10.1002/pc.750140502

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractA numerical simulation is presented that combines the flow simulation during injection molding with an efficient algorithm for predicting the orientation of short fibers in thin composite parts. Fiber‐orientation state is represented in terms of a second‐order orientation tensor. Fiber‐fiber interactions are modeled by means of an isotropic rotary diffusion. The simulation predicts flow‐aligned fiber orientation (shell region)near the surface with transversely aligned (core region) fibers in the vicinity of the mid‐plane. The effects of part thickness and injection speed on fiber orientation are analyzed. Experimental measurements of fiber orientation in plaque‐shaped parts for three different combinations of cavity thickness and injection speed are reported. It is found that gapwise‐converging flow due to the growing layer of solidified polymer near the walls tends to flow‐align the fibers near the entrance, whereas near the melt front, gapwise‐diverging flow due to the diminishing solid layer tends to lign the fibers transverse to the flow. The effect of this gapwise‐converging‐diverging flow is found to be especially significant for thin parts molded at slower injection speeds, which have a proportionately thicker layer of solidified polymer during the filling process. If the fiber orientation is known, predictions of the anisotropic tensile moduli and thermal‐expansion coefficients of the composite are obtained by using the equations for unidirectional composites and taking an orientation average. These predictions are found to agree reasonably well with corresponding ex

ISSN:0272-8397    

DOI:10.1002/pc.750140503

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractThe in‐plane flow of fluids through dense fibrous woven reinforcements was studied to aid the development of constitutive models for use in simulations of composite fabrication by resin transfer molding. As a first part of this effort, both one‐dimensional and radial flow experiments were conducted with Newtonian fluids in several woven glass fabrics. Analysis of the one‐dimensional flow experiments shows that the two experimental techniques are often, but not always, consistent, and both techniques suggest a relationship between the physical structure of the reinforcement and the mathematical structure of the permeability tensor. Preform features at the laminar and interlaminar scales were hypothesized to influence the experimental re

ISSN:0272-8397    

DOI:10.1002/pc.750140504

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractToughened and untoughened epoxy and BMI carbon fiber reinforced composites were evaluated in terms of their matrix chemical stability in galvanic reactions between metals and composites. It has been known that the presence of moisture and salts and contact between unprotected metals and BMI carbon fiber composition constitute prerequisite conditions for composite degradation. This study has further demonstarated that these conditions were necessary, but not sufficient. It was found that the OH species generated by galvanic reactions had to be concentrated in localized spots to induce composite degradation at a significant rate. A mechanism was proposed to elucidate how degradation took place under those necessary conditions with the aid of localized aggregation of the OH−species. Additionally, thoughening of BMI composite matrix resins resulted in poorer resistance to degradation by galvanic reactions. On the other hand, none of the eposy composites (toughened or untoughened) exhibited any degradation due to galvanic reactions at room temperature, nor did they degrade in a concentrated caustic NaOH solution (pH = 14,82°C) that simulated a highly accelerated galvanie reacti

ISSN:0272-8397    

DOI:10.1002/pc.750140505

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractThe thermal aging between 25 and 115°C of hot pressed glass fiber reinforced poly (methy1 methacrylate)(PMMA) transparent composites was studied as a function of the temperature and time of hot pressing. Thermal aging at near the Tgof the PMMA matrix caused dimensional changes and a reduction in optical transmission and clarity. The reduction in transmission was attributed to gas bubbles that formed in the matrix, which may be due to the evaporation of residual MMA monomer or low Tg(∼ 75°C) polymer in the composites during aging. Thermal cycling between 25 and 100°C by eliminating low Tgof the PMMA matrix establishes the upper temperature limit to which the composite can be exposed without seriously damaging its optical proper

ISSN:0272-8397    

DOI:10.1002/pc.750140506

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractA few years ago, polymer optical fiber (POF) emerged worldwide as a means for short optical transmission. This fiber type is generally made of poly(meth1 methacrylate) polymer and can be manufactured by a perform process using hot drawing in an oven. The mechanical properties, particularly the breaking stress, depend highly on the draw conditions. Recently, we have implemented the fabrication of very low diameter fiber, to take advantage of the electro‐optic properties of stumps of such single mode fiber. It turned out that the drawing conditions cause undesirable internal stresses, which, in turn, yield unfortunate refractive index variations in the fiber. We observed that increased shearing speed during the drawing operation of low diameter threads did provide high modulus fibers. To overcome the occurrence of the huge shrinkage at Tg, we have found that temperature and length of the oven are critical parameters: an increase in the temperature and also the length of the oven for a given drawing speed has resulted in quality PO

ISSN:0272-8397    

DOI:10.1002/pc.750140507

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractThe application of dynamic mechanical analysis (DMA) for quantifying interfacial interactions in composites is briefly reviewed. Carbon fiber/epoxy composites with fiber volume fractions of 12, 17, 38 and 61 vol% were subjected to flexural deformation on a Dupont DMA 983 instrument. The dependencies of dynamic mechanical properties of the composites on experimental parameters such as oscillation mode, amplitude, frequency, and temperature were investigate. As opposed to the storage modulus, the loss modulus is found to be sensitive to all parameters. In a fixed multiple frequency mode, the loss modulus of the composites increases with oscillation amplitude and decreases with frequency and the number of tests. The information produced in the resonant mode is more reproducible. An additional damping at the interfaces, apart from those of the constituents, suggests a poor interface adhesion in these composites. A linear relationship between the excess damping at the interfaces and the fiber volume fraction shows a similar interface quality for these composites having different fiber volume fractions. The detection of interfacial properities was found to be more sensitive in the flexural deformation mode than in the torsional mode. At temperatures higher than the glass transition temperature of the matrix, the effective volume fraction of the matrix is reduced. Such a reduction can be interpreted from the mismatch of thermal expansion of the matrix and the fibers.

ISSN:0272-8397    

DOI:10.1002/pc.750140508

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractPhysical blends and laminar composites of polystyrene (PS) and polyethylene (PE) were prepared with and without a tri‐block copolymer compatibilizer (poly(styrene‐block‐(ethylene‐co‐1‐butene)‐block‐styrene)), denoted SEBS. Dielectric strength and breakdown time of samples exposed to external partial discharges (PD) were measured and relationships were sought with composition, phase morphology, and phase bonding. The polymers were selected because they are incompatible and because the dielectric strength and stability towards PD are greater for PS than for PE. It was shown by adding small quantities of SEBS that a minimum amount of cohesive forces between the components was required to achieve good electrical properties. The major morphological factor controlling the electrical stability was which polymer constituted the continuous phase. Laminar composites with continuous sheets of stable PS as a top layer exhibited a stability equal to or better than that predicted from the upper bound

ISSN:0272-8397    

DOI:10.1002/pc.750140509

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractThe mechanical performance of advanced composite materials depends to a large extent on the adhesion between the fiber and matrix. This is especially true for maximizing the strength of unidirectional composites in off‐axis directions. The materials of interest in this study were PAN‐based carbon fibers (XA and A4) used in combination with a thermoset (EPON 828 epoxy) and a thermoplastic (liquid crystal poymer) matrix. The effect of surface treatment and sizing were evaluated by measuring the short‐beam shear (SBS) and transverse flexural (TF) tensile strengths of unidirectional composites. Results indicated that fiber surface treatment improves the shear and trasverse tensile strengths for both thermosetting and thermoplastic matrix/carbon fiber‐reinforced unidirectional composites. A small additional improvement in strengths was observed as the result of sizing treated fibers for the epoxy composites. Scanning electron microscope photomicrographs were used to determine the location of composite failure, relative to the fiber‐matrix interface. Finally, the epoxy composites SBS and TF strengths appear to be limited to the maximum transeverse tensile strength of the epoxy matrix, while the thermoplastic composite SBS and TF strengths are limited by the LCP matrix shear and transverse tensile strengths, res

ISSN:0272-8397    

DOI:10.1002/pc.750140510

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractCurrently, there is great interest in understanding and improving the bond between the fibers and matrix in high performcance composite materials. In many recently developed systems, fiber surface treatments have been developed to improve poor bonding. These treatments are often evaluated by measureing their effect on a composite property sensitive to the interfacial bond strength, typically the composite shear strength. This paper presents an evaluation of the influence of the matrix and interface properties on the transverse tensile strength. These effects were quantified by compring transverse flexural experimental data with results from a finite element micromechanics model. The results indicate that the transverse tensile strength is significantly more dependent upon sizing than is the shear strength. Finally, the transvere flexure test appears to provide an additional and complementary test for evaluating interface bond characteristics.

ISSN:0272-8397    

DOI:10.1002/pc.750140511

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY