摘要:

AbstractAlthough the question of minimum or critical fiber volume fraction, beyond which a composite can then be strengthened due to addition of fibers, has already been dealt with by several investigators for both continuous and short fiber composites, a study of maximum or optimal fiber volume fraction at which the composite reaches its highest strength has not been reported. The present analysis has investigated this issue for short fiber case based on the well‐known shear lag (the elastic stress transfer) theory. Using the relationships obtained, the minimum spacing between fibers is determined upon which the maximum fiber volume fraction can be calculated. The effects on the value of this maximum fiber volume fraction due to such factors as the mechanical properties of the fiber and matrix, the fiber aspect ratio, and fiber packing forms are discussed. Furthermore. Combined with the previous analysis on the minimum fiber volume fraction, this maximum fiber volume fraction is used to examine the property compatibility of fiber and matrix in forming a composite. This is deemed to be useful for composite design. Some examples are provided as well to illustrate the result

ISSN:0272-8397    

DOI:10.1002/pc.750140202

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractGlass microscope slides were initially used to develop a technique for bonding UHMWPE films on to glass and polyamides respectively, as well as to provide a simple physical model for interlayered fiber composites. Further experiments were carried out on glass fibers coated with UHMWPE from a xylene solution, in order to evaluate the applicability of the above technique and of the physical model in actual composite systems. Although great difficulties were encountered in achieving a well boned uniform coating on the glass fibers the results have confirmed the viability of the approach: the impact strength of compression molded glass reinforced Nylon plaques, measured with an instrumented falling weight apparatus, was increased considerably with only a corresponding small loss in flexural modulus. Dynamic mechanical analysis results indicate that a UHMWPE interlayer substantially increases the tan δ of the short fiber composite over a wide temperature range, albeit with some reduction in modulus

ISSN:0272-8397    

DOI:10.1002/pc.750140203

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractComputer modeling is used in order to provide a theoretical understanding of the concept of critical length in composites, and of the factors influencing the critical aspect ratio. The effects of interphase and matrix properties have been investigated. We have identified the interphase parameters which minimize the critical length. Contrary to the assumption that the critical aspect ratio is related to interfacial shear strength and fiber strength only, we find a significant dependence on matrix viscosity and strain rate, for fixed interphase properties. We therefore conclude that the fragmentation test, which relates the measured critical aspect ratio to a value for the interfacial shear strength, has to be reinterpreted in terms of more parameters than those simply present in the Kelly‐Tyson formalism. Moreover, the significance of the concept of critical length for tailoring mechanical properties of composites needs to be reassesse

ISSN:0272-8397    

DOI:10.1002/pc.750140204

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractThe variation of fiber orientation and content within injection molded rectangular plates is investigated. Fiber orientation and volume fraction are measured using metallographic polishing and a newly developed image‐analysis system; fiber weight‐fractions are measured using an ashing method. Three different moldings are studied; two of the long‐fiber compound Verton, Molded at different injection speeds, and one of the short‐fiber compound Maranyl. Microstructural regions are identified and characterized, and the flow mechanisms by which they are formed are discussed. The results show that the long fibers segregate extensively, whereas the short ones do not. The major differences between the two compounds are found in the core: the core of the long‐fiber compound has a higher content and orientation of fibers than that of the short‐fib

ISSN:0272-8397    

DOI:10.1002/pc.750140205

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractA technique that uses digital image processing to measure the orientation distribution function of the fibers in a plane of a short‐fiber composite is described in this work. Other orientation descriptors, such as the fiber orientation parameter, can be calculated from the measured fiber orientation distribution function. In this technique, the edges of the fibers in a digital image of the composite are first identified. Then, using Sobel operators, the orientation of the gradient vector is determined at each fiber orientation distribution function. The advantages of digital imaging over photography and the simplicity of the algorithms make this technique advantageous over previously developed methods to measure fiber orientatio

ISSN:0272-8397    

DOI:10.1002/pc.750140206

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractThe self‐consistent method and finite element simulations have been used to estimate the permeability of an aligned fiber bundle. The self‐consistent method gives out formulas for both longitudinal and transverse permeabilities as functions of the fiber volume fraction. The finite element simulation presents the solutions of various periodic fiber packings. The results for square and hexagonal fiber packings are found coincident with the literature results. It is shown that the permeability is not only related to the fiber volume fraction of porosity, but is also greatly influenced by the packing structure or micro‐level disturbance. A unified empirical model is proposed, which uses as variables ultimate fiber volume fraction in addition to fiber volume fraction. The model predications agree with numerical simulation results in different

ISSN:0272-8397    

DOI:10.1002/pc.750140207

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractWhen a resin in injected into the mold in liquid composite molding, the preplaced fiber mat may deform near the inlet gate because of the high momentum carried by the injected fluid. A fiber free region near the gate followed by the fiber mat deformation may emerge. This phenomenon is most likely to occur when the stacked fiber mats have low permeability and the resin has high viscosity. A set of mold filling experiments were carried out using an instrumented metal mold and a small transparent mold to investigate the fiber mat deformation during mold filling. Experimental results showed that the fiber mat deformation was limited to a small region near the gate and that deformation greatly reduced the molding pressure. A forced fiber mat deformation employing a modified gate design was proposed to facilitate mold filling in liquid composite molding.

ISSN:0272-8397    

DOI:10.1002/pc.750140208

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractMathematical models are proposed to simulate the flow induced fiber mat deformation during liquid composite molding. The fiber bed is treated as an elastic beam and the load acting on the bed causes its deformation. The lubrication approximation is used to simplify the resin flow equation in the fiber free region, while Darcy's law is used to calculate the pressure and velocity fields in the deformed fiber bed. The governing equations are solved using the control volume/finite element method. The numerical results show reasonable agreement with the experimental results from Part I.

ISSN:0272-8397    

DOI:10.1002/pc.750140209

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractIn this study, systematic investigation of influence of processing variables on the tensile strength and resin‐fiber interface of composites prepared by liquid composite molding process was carried out. The variables studied included injection pressure and mold/fiber mat temperature. Fibers were better wetted and bonded at lower injection pressure and higher molding temperature, which resulted in a higher tensile strength of molded composites. Single filament composite tests were also used in conjunction with birefringence studies to characterize interface bonding. Improved interfacial behavior was observed in the case of compatible system

ISSN:0272-8397    

DOI:10.1002/pc.750140210

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

ISSN:0272-8397    

DOI:10.1002/pc.750140201

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY