DOI:10.1163/156855497X00019

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

_We consider fragmentation experiments as a set of experimental results for fiber break density as a function of applied strain. This paper explores the potential for using fracture mechanics or energy methods in interpreting fragmentation experiments. We found that energy does not control fiber fracture; instead, fiber fracture releases much more energy than required to fracture the fiber. The excess released energy can lead to other damage mechanisms such as interfacial debonding. By assuming that all the excess released energy causes interfacial debonding and balancing energy using the energy release rate for debonding, we were able to determine interfacial toughness from fragmentation experiments. A reliable determination of interfacial toughness requires prior knowledge of interphase stress-transfer properties, fiber failure properties, actual damage mechanisms, and the coefficient of friction at the interface.

DOI:10.1163/156855497X00028

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Multicomponent polymer blends, for improving both process and product related properties, often require the optimization of interfaces/ interphases. This is particularly true in the case of blends based on recycled polymers. Besides a review of existing approaches, two examples are presented in more detail. The former is related to the toughening of recycled PET (poly(ethylene terephthalate)) by reactive ethylene-ethyl acrylate_glycidyl methacrylate elastomers. The effect of catalysts of the reaction between elastomer epoxide functions and PET carboxyl and hydroxyl end-groups and of impurities introduced during recycling has been assessed. Variations of rheological behavior, morphology of chips and molded parts, and mechanical properties have been examined and related to interfacial chemistry. The formulation with glass fibers has also been experimented with, gaining interesting information on the compromise between resilience and rigidity. The second example is related to the so called 'light fraction' of recycled polymers, concerning mainly polyethylene (PE) and polypropylene (PP). Mixing has been performed in various relative amounts, as such and in the presence of initiators inducing both bulk and interfacial radical reactions. Effects on rheology, morphology and mechanical properties have been assessed, observing that the initiation of reactions is an important tool for improving the interfacial behavior.

DOI:10.1163/156855497X00037

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The interface region in a given composite has a great deal of importance in determining the ultimate properties of the composite. An interface is, by definition, a bidimensional region through which there occurs a discontinuity in one or more material parameters. In practice, there is always some volume associated with the interface region over which a gradual transition in material parameter(s) occurs. The importance of the interface region in composites stems from two main reasons: (i) the interface occupies a very large area in composites, and (ii) in general, the reinforcement and the metal matrix will form a system that is not in thermodynamic equilibrium. One can discuss the interface in a composite at various levels. An optimum one should be neither so simple that it covers only a few special cases nor so complex that it is not useful in designing composites from processing and applications points of view. In this paper, my objective is to give examples of interface microstructure in different metal matrix composite systems and suggest some ways of controlling the interface characteristics in order to control the properties of the composite. I shall give examples of the interface microstructure in different metal matrix composites (particle and fiber reinforced as well as laminates) and discuss some of the important implications on various aspects of metal matrix composites, from the processing stage to ultimate performance of the composite.

DOI:10.1163/156855497X00046

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Adhesion is vital to composites because cracks are stopped at adhesive interfaces, deflected along them, or converted into interfacial dislocations. Failure is therefore dominated by the adhesion between the components of the composite. This paper describes new ideas about adhesion and considers the relevance of these ideas to composite materials. In particular it emphasises the difference between adhesion at the molecular level and adhesion in engineering terms. There is no doubt that molecules of solid materials are attracted to each other by van der Waals and other influences. Also, they can be separated by applying mechanical forces. The problem is explaining the connection, i.e. the mechanism, between molecular attractions and mechanical measurements. Ideas such as 'keying', 'glueing' and 'friction' require critical assessment because they operate differently at the molecular scale. Interesting mechanisms such as 'adhesive hysteresis', 'adhesive stringing', and 'adhesive aggregation' deserve evaluation. A rational theory of these and other interface phenomena should be based on the theoretical concept of reversible work of adhesion. However, it is necessary to distinguish this thermodynamic work of adhesion from the measured quantity of adhesive energy, which includes the extra energy required to restructure the interface as surfaces move.

DOI:10.1163/156855497X00055

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The fibre/matrix interaction is a critical aspect of the composite behaviour for all composite families and has to be optimized for each new fibre/matrix system. In order to help this optimization, dedicated tests on model composites have been developed since fibre adhesion to organic matrices was first measured reproducibly in terms of bonding strength in the early sixties. Such tests provide a lot of information about the interface and related microphenomena and thus help to improve the materials. The progress is especially fast whenever the material is in an early stage of development. However, difficulties in the mechanical analysis of those apparently simple tests stand in the way of the introduction of relevant parameters into models of composite behaviour.

DOI:10.1163/156855497X00064

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

A series of PAN-based IM6 carbon fibers which were surface treated to different levels with a commercial method were pretreated with compounds representing the constituents encountered in epoxy matrices used in composites. This was done to pre-react any groups on the fiber surface with these compounds before composite fabrication in order to determine the effect of chemical bonding on fiber-matrix adhesion. The extent of chemical bonding was quantified using X-ray Photoelectron Spectroscopy (XPS). Chemical bonding between reactive groups in amine cured epoxy matrices and the surface groups present on these IM6 carbon fibers has been determined to be low (1_3%). Pre-reaction with the monofunctional epoxy compound (butyl glycidyl ether) eliminated the possibility of further reaction with the epoxy matrix and the fiber-matrix adhesion that was measured was the lowest value. Pre-reaction with the difunctional amine compound had no measurable effect on adhesion when compared to normal composite fabrication procedures. Pre-reaction with the difunctional epoxy compound however did increase adhesion levels over that attained without any pretreatment encountered in normal composite fabrication methods. These results showed that when compared to physical interactions between the fiber surface and the epoxy matrix alone, chemical bonding between the epoxy and the carbon fiber surface could increase the adhesion between fiber and matrix by about 34% while chemical bonding between the amino group and the carbon fiber surface can increase adhesion by about 18%. Quantitative measurements of the fiber surface microtopography were made with scanning tunneling microscopy. A systematic increase in the nanoscale topography (roughness) of the fiber surface was detected with increasing surface treatment. When quantified, it was concluded that surface roughness similarly accounted for a significant increase in fiber-matrix adhesion. Overall, it was concluded that the addition of the surface chemical groups that react with the matrix and are produced during surface treatment are added on a surface that is increasingly rougher. Both effects combine synergistically to increase fiber-matrix adhesion.

DOI:10.1163/156855497X00073

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor