摘要:

A thermodynamic evaluation, based on simultaneous measurements of the mechanical work and the concomitant heat of deformation in a stretching micro calorimeter, was performed on polycarbonate/carbon fibre (PC/CF) micro composites. Single fibre composite specimens containing sized and unsized CF were subjected to different thermal treatments. Thermodynamic effects of deformation were measured for both elastic and plastic deformation ranges. In the elastic/beginning of plastic deformation ranges the internal energies and heat effects of deformation of micro composites exceeded those of matrices. The highest internal energy and, in turn, the highest fibre/matrix adhesion, was found in the case of the quenched micro composites with sized fibers. Thermodynamic effects of deformation and calculated material constants of PC were in reasonable agreement with data in the literature.

DOI:10.1163/156855496X00010

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Fibre pull-out experiments have been carried out to compare the behaviour of reactive and non-reactive fibre-reinforced metal systems. The test samples were made by melting the metal matrix in vacuum and lowering the fibre a known depth into the liquid. In all cases some brittleness appeared to develop, since final interface failure, except with steel-99% AI, was sudden, and the values of the debonding force were quite scattered in all cases. Otherwise the results agreed with earlier observations, i.e. a linear increase in debonding force with increasing embedded length until the force was high enough to break the fibre rather than debond it. Some yielding was noticeable before failure. An elasticity analysis suggested that high shear stresses were needed in some cases to initiate yielding. However, the interface strengths, as indicated by the debonding forces, were no more than about twice the shear yield stresses of the matrices, as indicated by compressive tests on the metals. A reaction layer was observed on steel which was embedded in the aluminum, but this did not appear to reduce the interface strength. With W-Cu, on the other hand, a thin layer of copper was present on the pulled out tungsten fibre, while with SiC-AI, the silicon carbide had some carbon present on the surface, with traces of AI.

DOI:10.1163/156855496X00029

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

This paper describes the radical graft polymerizations of vinyl monomers from carbon fiber surface initiated by azo groups introduced onto the fiber surface. The carbon fiber used in this experiment was the polyacrylonitrile type. The introduction of azo groups onto the carbon fiber surface was achieved by the reaction of 4,4'-azobis (4-cyanopentanoic acid) with isocyanate groups which were previously attached onto the surface by the treatment of the fiber with tolylene 2,4-diisocyanate. The amount of surface azo groups introduced onto nitric acid-treated carbon fiber was determined to be 0.60 x 10-5mol 9-1by nitrogen analysis. The radical graft polymerization of methyl methacrylate (MMA) was tried. Though the thermal polymerization of MMA proceeded slightly in the absence or in the presence of untreated carbon fiber, the rate of the polymerization was considerably low. In contrast, the graft polymerization of MMA was initiated in the presence of the carbon fiber having surface azo groups, and part of resultant poly(MMA) grafted onto the surface. The percentage of grafting increased with an increase in polymerization time and reached 42.8% after 24 h. The graft polymerizations of other monomers, such as styrene, vinyl acetate, and acrylic acid, were also initiated by the surface azo groups attached onto the carbon fiber, and the corresponding polymer effectively grafted onto the surface.

DOI:10.1163/156855496X00038

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Debonded fibers influence the macro-mechanical behavior of fiber-reinforced composite materials. Debonded fibers contribute to the initiation and growth of cracks at the fiber/matrix interface. To examine such problems, the scattering of elastic SH-waves (problem of anti-plane strain) from debonded fibers is studied with a numerical method which can handle the mixed boundary conditions on the partially bonded fiber. A modification of the null field of T-matrix method is developed for this purpose. The modification is achieved by the introduction of a mathematical surface. The simultaneous solution of the integral representations of the field scattered by the mathematical surface and the actual fiber surface give rise to sufficient equations that permit solution of the debonded fiber problem. The scattering cross-section and the far field amplitude are calculated as a function of frequency, fiber properties and debonding area. This will be of interest in structural applications where such cross-sections can be used to compute the dynamical effective properties of damaged composites.

DOI:10.1163/156855496X00047

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

_The effect of surface treatment on mechanical properties of carbon fibers has been investigated by application of plasma polymerization of selected monomers in the vapor phase. The role of the fiber-matrix interface on carbon fiber-reinforced epoxy resin composites has also been studied. Composites have been prepared separately by the use of plasma-modified and unmodified carbon fibers in the epoxy resin matrix. The mechanical properties of carbon fibers (Hercules and Grafil) as well as of fiber/epoxy composites were examined by using single filament and three-point bending tests, respectively. It was observed that plasma polymerization treatment at selected plasma conditions led to significant improvement of interlaminar shear and flexural strength values of composites.

DOI:10.1163/156855496X00056

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The properties of a composite component are widely influenced by the conditions it experiences in service. The interface plays an important role in determining the mechanical properties of a composite and therefore it is necessary to understand its behaviour under environmental conditions. One of the most widely used techniques for the evaluation of the fibre/matrix interface is the single fibre fragmentation test. The conventional analysis of this test relies on reaching a state where the fibre becomes saturated with breaks; a state which is not always achievable especially at low temperatures or high strain rates. This study examines and relates the development of resin cracks initiated from fibre breaks throughout a test, at elevated temperatures and over a defined range of strain rates. The monitoring of the size and morphology of these resin cracks is proposed as a qualitative method of evaluating the strength of the fibre/matrix interface. Secondly, the validity of analysing fragment lengths with respect to their strength prior to saturation is demonstrated on data obtained with fibres at various interfacial treatment levels. This method requires the continuous recording of the number of fibre breaks at increments of strain throughout the test. Fragment lengths are then compared at a stress below saturation.

DOI:10.1163/156855496X00065

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

There has been growing interest recently in study the means for modifying material parameters of SAW substrate surfaces in a controllable way. The problem is of considerable practical importance both in relation to optimization of SAW characteristics, especially in a high frequency region, as well as to make them adaptable to changeable conditions. To clearly understood and control these features and for improved device design, it is important to have a reliable theoretical model for dynamical behaviour of substrates with structurally modified near-surface layers. The purpose of this paper is to set forward a systematic approach to model the local changes in elastic and quasielastic parameters as produced by point centres of microdistortion, selectively introduced into the near surface region of some higher symmetry substrates. To make the problem tractable for conditions existing at real surfaces, with a generally complex internal microstructure, the treatment is formulated in terms of a nonlocal theory of elasticity using, locally averaged over microscopic details, multipole material and field characteristic. The method will be illustrated for an impurity-induced realization of a periodic 2D grating composed of clusters of another phase with an externally controlled profile.

DOI:10.1163/156855496X00074

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The problem of stability of interfaces in metal matrix composites is reduced to the investigation of the solubility and diffusion processes of fiber atoms in the metal matrix. The calculations of excess thermodynamic functions of interstitial solid solutions is performed. The influence of additives on the stability of intermetallic phases formed at the interfaces is discussed. The height of diffusion barriers for aluminium and copper matrix composite materials with carbon or boron fibers is calculated. It is shown that the alloying of the matrix by additional element, substituting aluminium or copper in the interstitial metal-metalloid solid solution, changes the value of the barrier and influence the diffusion of metalloid. Some additives as the best alloying elements for preventing the diffusion in the alloys studied are predicted.

DOI:10.1163/156855496X00083

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor