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The effects of an imperfect thermal interface on the thermal fields by studying a single, spheroidical inclusion embedded in an infinite isotropic matrix is described. The method enables one to estimate the locations and magnitudes of the minimum and maximum temperature gradients within the inclusion.

Byline: S.N.R. Choudhury, A. Edwards, M. Provatas The focus of the present study is to understand the effect of injection moulding process parameters on the surface finish of PC/ASA (polycarbonate/acrylonitrile-styrene acrylate) moulded parts through the analysis of both the bulk and surface chemical behaviours. Thermogravimetric analysis (TGA) provided information on material composition, thermal stability and decompositional behaviour, while Photoacoustic Fourier Transform Infrared Spectroscopy (PA-FTIR) was used to identify the effect of injection moulding on the chemical structure of the composite material. Microscopic analysis of surface defects was accomplished via Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). Bulk analysis by TGA showed that the thermal stability of parts was lower when manufactured at extreme material temperature, injection speed and pack pressure. Surface chemical structure was found unchanged by PA-FTIR while SEM showed the surface topography of a defect known as 'pearlescence' often present on grained parts. AFM successfully visualised the melt flow pattern and how it related to the surface finish on the moulded plaques.

Byline: David Attwood, Jonathan Hodgkin, James Mardel, Healther St John The aim of the project that is described in this paper is to develop low-cost chemical and physico-chemical methods of testing and analysis of new composite materials. This will enable the aerospace industry to predict aspects of the lifetimes of composite aerospace parts without the standard, but very expensive, mechanical testing regimes normally required. The initial section of the project has been designed to build up an under-standing of what are the environmental conditions seen by materials on modern aircraft and which of these are critical to the determination of composite lifetimes. Preliminary accelerated testing trials have shown which types of chemical analyses give the most relevant information. It has also been shown that extensive calibration of equipment and careful experimental design are required, especially when the testing conditions get closer to the 'in service' environments. Results of analyses from some actual aerospace samples have also been carried out for comparison purposes.

A systematic presentation of the concept of a well-defined stochastic damage accumulation model for fatigue calculation is attempted; the model is applicable for both organic and ceramic matrix composites. Stationary and nonstationary, with one or more blocks, discrete time and finite state Markov chain models are employed. They are found appropriate for yielding fatigue life probability distributions and damage evolution information at different stress levels. The structure, applicability, flexibility, and limitations of the model are examined in detail. The theoretical concepts are elucidated by the incorporation of data from a comprehensive testing program.

Composite materials consisting of polystyrene-coated iron nanoparticles were prepared by the thermal decomposition of iron pentacarbonyl in the presence of polystyrene-tetraethylenepentamine dispersants. The nanocomposites contain both simple core-shell particles of 10-20 nm diameter, and more complex particles (20-100 nm) made from the agglomeration of several core-shell particles. Electron diffraction revealed that the core was composed of iron, in contrast to the iron nitride ([Fe.sub.3]N) reported for similar conditions with a polyisobutylene-based dispersant. The materials exhibit hysteresis and [[Sigma].sub.s] ranges from 7.6 to 29.3 emu/g. The coercivity goes through a maximum for particles of [approximately equal] 25 nm diameter. Removal of unbound dispersant from the materials greatly increases the magnetization. Index Terms--Core-shell, iron-polystyrene composite, magnetic nanoparticle, polystyrene-tetraethylenepentamine dispersant.

Thermodynamically consistent constitutive equations are derived here in order to investigate size effects on the strength of composite, strain, and damage localization effects on the macroscopic response of the composite, and statistical inhomogeneity of the evolution-related damage variables associated with the representative volume element. This approach is based on a gradient-dependent theory of plasticity and damage over multiple scales that incorporates mesoscale interstate variables and their higher order gradients at both the macro-and mesoscales. This theory provides the bridging of length scales. The interaction of the length scales is a paramount factor in understanding and controlling material defects such as dislocation, voids, and cracks at the mesoscale and interpreting them at the macroscale. The behavior of these defects is captured not only individually, but also the interaction between them and their ability to create spatiotemporal patterns under different loading conditions. The proposed work introduces gradients at both the meso- and macroscales. The combined coupled concept of introducing gradients at the mesoscale and the macroscale enables one to address two issues simultaneously. The mesoscale gradients allow one to address issues such as lack of statistical homogeneous state variables at the macroscale level such as debonding of fibers in composite materials, cracks, voids, and so forth. On the other hand, the macroscale gradients allow one to address nonlocal behavior of materials and interpret the collective behavior of defects such as dislocations and cracks. The capability of the proposed model is to properly simulate the size-dependent behavior of the materials together with the localization problem. Consequently, the boundary-value problem of a standard continuum model remains well-posed even in the softening regime. The enhanced gradient continuum results in additional partial differential equations that are satisfied in a weak form. Additional nodal degrees of freedom are introduced that leads to a modified finite-element formulation. The governing equations can be linearized consistently and solved within the incremental iterative Newton-Raphson solution procedure.

A multizone nonlinear boundary element method is used to simulate the size effect of quasi-brittle materials that are modeled as randomly dispersed particulate composites with randomly distributed microcracks located between the particles and matrix. Usually a series of geometrically similar specimens are used to describe the size effect of materials. In this paper, a one-size specimen method for determining the fracture energy [G.sub.f] and effective process zone length [c.sub.f] is proposed and verified by numerical simulation. The specimen used for boundary element simulation is confined to only one shape and one size but with different initial crack lengths. A three-point-bend beam and a compact tension specimen are used to expand the range of brittleness number and therefore increase the degree of confidence of the results. Notchless specimens of the same size are also calculated and used to supplement the data of one-size notched specimens. The shape, size, and location of the fracture process zone caused by development of microcracking are observed. The results of [G.sub.f] and [c.sub.f] obtained from the one-size specimen method are compared with a commonly used method and a good agreement is shown.

This project was conducted to evaluate the performance and leaching of controlled low strength materials (CLSM) incorporating fly ash and foundry sand. Two different CLSM (or flowable slurry) reference mixtures (equivalent to available production CLSM mixtures) were proportioned for unconfined compressive strength levels in the range of 0.3-0.7 MPa (50-100 psi), at 28 days, using two sources of ASTM Class F fly ash. For each reference mixture, other mixtures were proportioned using two sources of foundry sand (molten metal-casting mold sand) as a replacement for fly ash in the range of 30-85%. The ingredients of the slurry mixtures--fly ash, clean foundry sand, and used foundry sand--were tested for their physical and chemical properties and their leachate characteristics. Portland cement used as the primary binder was also tested for its properties. All CLSM mixtures made with and without foundry sand were evaluated for settlement, setting and hardening characteristics, compressive strength, permeability, and leachate characteristics. The leachate results of these CLSM-making materials were below the enforcement standards (ES) of the Wisconsin Department of Natural Resources (WDNR) ground-water quality standards (GWQS). They also met practically all the parameters of the drinking water standards. A number of CLSM mixtures incorporating fly ash and foundry sand are recommended for construction applications.

The development of composite insulators in China dates back to the early 1970's. In the 1990's they have become widely used in China. At present, up to 600000 composite insulators are operating on 35 to 500 kV ac overhead transmission lines. They are to be introduced into the [+ or -]500 kV HVDC transmission schemes. In China all composite insulators in service are silicone rubber and are operating in various contamination conditions. They have successfully and efficiently avoided serious pollution flashover, which occurred frequently when conventional ceramic insulators were used, and radically reduced the maintenance cost of transmission lines in pollution areas. Study of composite insulators is very active in China. The main aspects include properties of materials such as silicone rubber and fiberglass reinforced polymer (FRP) rods, electrical and mechanical performance, aging as well as evaluation and inspection of composite insulators. These fruitful works greatly promote the development of composite insulators in China.

This paper summarizes the result of the questionnaire on current status of non-ceramic (composite) insulators in the world conducted by the Non-ceramic (composite) Insulators Technical Committee, Japan. Current use status, reasons for use, maintenance, failure occurrence and research activity of 16 responding utilities are described. About 80% of the responding utilities answered that they would actively increase the use of non-ceramic (composite) insulators in the future. It is anticipated that the market for these insulators will keep expanding.

In practical analysis, under a plane stress condition, a unidirectional lamina can be assumed with [E.sub.2] = [E.sub.3] from geometrical symmetry consideration. However, from an academic point of view, it is interesting to study the case of a lamina with [E.sub.2] [not equal to] [E.sub.3]. In this paper the preliminary results of the physical phenomenon about the effect of different transverse moduli [E.sub.2] and [E.sub.3] on the through-thickness thermal expansion coefficients [[alpha].sub.z] of quasi-isotropic composite laminates is presented. [DOI: 10.1115/1.1410937]

This paper presents a multilayered/multidirector and shear-deformable finite-element formulation of shells for the analysis of composite laminates. The displacement field is assumed continuous across the finite-element layers through the composite thickness. The rotation field is, however, layerwise continuous and is assumed discontinuous across these layers. This kinematic hypothesis results in independent shear deformation of the director associated with each individual layer and thus allows the warping of the composite cross section. The resulting through-thickness strain field is therefore discontinuous across the different material sets. Numerical results are presented to show the performance of the method.

A study was conducted to analyze a five-layer framework to examine the anisotropic constraint effects on interactive damage progression. The model was integrated with the general theory of overall moduli of a cracked body. Experimental results indicated that the intractable problem of anisotropic constraint effects of general lay-up composites on interactive damage progression can be determined in a systematic way.