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Two doping methods that specifically use the holey nature of mPOF are discussed. Dopants or particles can be introduced into the holes of the preform or the cane. Both methods are described here, and results showing the fluorescence from fibres doped with organic dyes, embedded organo-silica nanoparticles and quantum dots are presented. Indeed, an mPOF laser has been demonstrated using the solution doping method. [ABSTRACT FROM AUTHOR]

This chapter describes both Fibre Bragg Gratings (FBG) and Long Period Gratings (LPG) in mPOF, and the required theoretical basis to understand their operation. Gratings are a highly developed research area, and no attempt has been made to review the whole field. Excellent reviews are available, including [Othonos and Kalli 1999, Kashyap 1999]. The two most relevant related areas however are described here: gratings in MOFs and POFs. This work is significant in identifying applications where the material or waveguide properties of mPOF may offer new functionality. The chapter also describes the experimental techniques used to make mPOF gratings, and their performance characteristics. Finally, conclusions are drawn about how mPOF gratings may be improved and application areas where they may prove useful. [ABSTRACT FROM AUTHOR]

In this chapter we describe the factors that limit the bandwidth of large-core multimode polymer fibres, including intramodal and intermodal dispersion. The latter is usually addressed by using a graded-index (GI) to equalise the group velocities of the fast and slow modes. While most GI fibres use differences in chemical composition to produce the index gradient, it is also possible to use a graded microstructure. Such fibres (denoted GImPOF) differ from conventional GI POF not just in having a microstructure, but also in having a much larger index contrast. We model the behaviour of a non-microstructured (i.e. azimuthally averaged) fibre with the same contrast. We present the modelling and experimental results for a GImPOF and assess its potential. [ABSTRACT FROM AUTHOR]

This chapter is devoted to mPOFs that guide in a hollow core. It describes two methods for fabricating these fibres and explains their transmission characteristics. Common issues affecting the performance are discussed as well as the various applications. [ABSTRACT FROM AUTHOR]

This chapter outlines three methods for cutting mPOFs as well as giving details of techniques that have been used to characterise mPOFs through accurate imaging of their microstructure as well as outlining measurements of their light guiding properties such as loss, numerical aperture, bandwidth and birefringence. [ABSTRACT FROM AUTHOR]

The stretch and drawing processes used to make mPOF pose considerable computational challenges, combining as they do non-isothermal, threedimensional (3-D) and time dependent behaviour. This complexity is further complicated if the materials used exhibit significant nonlinear viscoelastic behaviour, while the very nature of an mPOF means that its fabrication involves the substantial deformation of a (potentially large) number of 3-D free surfaces. Unsurprisingly the relevant analytical [Fitt et al. 2002] and numerical [Deflandre 2002, Lyytikäinen et al. 2004] literature is limited. However a convincing story has recently emerged that quantitatively ties together the roles of material properties and tower draw conditions in determining both hole size and shape deformation within an overall MOF structure. This chapter begins with a scaling analysis leading to a suite of dimensionless numbers whose values can be used to assess the relative importance of the viscous, inertial, gravitational and surface tension forces in any particular drawing process. Subsequently both isothermal and non-isothermal drawing are considered. In the former case indicative theoretical analysis is possible, while in the latter it is necessary to rely on numerical modelling. Both hole size and shape changes are considered. Although the focus is on polymer fibres, consideration is also given to silica based microstructured optical fibres so as to highlight the impact of differing material properties. The chapter concludes by considering the impact of hole pressurisation during the draw process. [ABSTRACT FROM AUTHOR]

Conceptually, the fabrication of microstructured polymer optical fibre is a straightforward process involving just two steps - the creation of a preform containing a large-scale version of the structure desired in the fibre, followed by heating and drawing of the preform to produce the final fibre. Three issues soon emerge however when trying to turn this simple two-step process into a reality. [ABSTRACT FROM AUTHOR]

The first part of this chapter is about algorithms for modelling microstructured fibres. We also begin by briefly summarising the two major conventions for naming modes. The ideas behind the algorithms for calculating modes are then discussed but detailed results available in the literature are not reproduced here. It is impossible to be comprehensive or even perfectly balanced when covering such a wide field. Some references to both commercial and free software are given. We also sometimes give examples of how these algorithms have been used to analyse interesting features of microstructured fibres. [ABSTRACT FROM AUTHOR]

This chapter builds on the concepts in Chapter 2 but focusses on differences between microstructured and conventional fibres. It begins with a description of the two different guidance mechanisms specific to MOFs. It then goes on to discuss two important ways in which the optical properties of MOFs differ from conventional fibres, namely confinement loss and dispersion. An understanding of these differences is crucial to appreciating how MOFs have expanded the ways and the range in which optical fibres can be used. [ABSTRACT FROM AUTHOR]

This chapter assumes the reader is familiar with the basic undergraduate optical concepts of electromagnetic waves, refractive index, phase, polarisation, diffraction and interference. The focus is on the important concepts, and although in this chapter we only look at conventional fibres we examine the concepts with sufficient clarity to ensure that they will be correctly applied to microstructured fibres. We also discuss whether a concept has a primarily historical, pragmatic or theoretical basis. Mathematical formalism is kept to a minimum while retaining as much rigour as necessary, and most of the approximations presented are based on sound theoretical concepts. We begin with how modes are classified and the role of polarisation and birefringence. We then move on to counting modes and the important concept of cutoff. We look at coupling light into fibres and then at dispersion. Finally, we cover the physics behind how modes are confined in conventional fibres to prepare the reader for the next chapter. [ABSTRACT FROM AUTHOR]

This chapter places the rest of the book in context. It describes the history and state-of-the-art of both polymer fibres (POFs) and microstructured optical fibres (MOFs). The physical properties of these fibre types differ considerably in terms of the materials used and the possible waveguide geometries, and these form the basis for the difference in their applications. This chapter outlines both the physical differences and the major applications of each. The applications of POFs are described in more detail because most of the applications of microstructured fibres reappear in later chapters. [ABSTRACT FROM AUTHOR]

During the last few years, novel structures, phenomena, and processes have been observed at the nanoscale. In addition, the very nature of thermal and mechanical responses of materials is governed by the phenomena occurring at the atomic nanoscale. With the development in nanoscale systems, there is an urgent need for theory, modeling, and computational tools to understand and accelerate development and applications. Modeling efforts in nanoscale systems have predominantly used atomistic simulations based on molecular dynamics or other refined techniques, such as density functional and tight binding theories, which help clarify the issues involved at the macroscale. Though atomistic simulations provide insightful details into many problems of interest, the exceedingly high computational requirements of atomistic simulations place a stringent limitation on length and time scales for the problem of interest. [ABSTRACT FROM AUTHOR]

The increased computational power and programming capabilities in recent years have given impetus to the so-called multiscale modeling, which implements the largely intuitive notion that physical phenomena occurring at a lower length or size scale determine the observed response at a higher scale. A logical outcome of this thought is an organization of differentiated scales - from the lowest, such as nanometer scale, to the highest scale typical of the part or structure in mind - giving a hierarchy of scales. Working up the scales produces a hierarchical multiscale modeling, in which the essential challenge consists of "bridging" the scales. The simulation techniques, such as molecular dynamics simulation (MDS), succeed mostly in revealing phenomena from one scale to the next; but proceeding to three or more scales often necessitates unrealistic computing power even with the most versatile facilities available. In addition, the limitation of independent physical validation of the simulated results questions the wisdom of total reliance on the multiscale hierarchical modeling strategy. When it comes to subcritical (prefailure) damage in composites, the multiscale modeling concept needs closer examination, firstly, because the length scales of constituents and heterogeneities are fixed while those of damage evolve progressively, and secondly, because the mechanisms of damage tend to segregate in modes with individual characteristic scales. All this is the subject of this chapter, which will first describe and clarify the damage mechanisms in common types of composites followed by the induced response observed at the macroscale. The hierarchical modeling approach will be discussed against this knowledge; and a different approach, named synergistic multiscale modeling, will be advocated. Assessment will be offered of the current state of this modeling, and future activities aimed at accomplishing its objectives will be outlined. [ABSTRACT FROM AUTHOR]

It has long been recognized that one of the primary failure modes in solids is due to crack growth, whether it be a single or multiple cracks. It is known, for instance, that Da Vinci [14] proposed experiments of this type in the late fifteenth century. Indeed, modern history is replete with accounts of events wherein fracture-induced failure of structural components has caused the loss of significant life. Such events are common in buildings subjected to acts of nature, such as earthquakes, aircraft subjected to inclement weather, and even human organs subjected to aging. Therefore, it would seem self-evident that cogent models capable of predicting such catastrophic events could be utilized to avoid much loss of life. However, despite the fact that such events occur regularly, the ability to predict the evolution of cracks, especially in inelastic media, continues to elude scientists and engineers. This appears to be at least due, in part, to two as yet unresolved issues (1) there is still no agreed upon model for predicting crack extension in inelastic media and (2) the prediction of the extension of multiple cracks simultaneously in the same object is as yet untenable. While it would be presumptuous to say that the authors have resolved these two outstanding issues, there is at least a glimmer of hope that these two issues may be resolved by using an approach not unlike that proposed herein. This chapter outlines an approach for predicting the evolution of multiple cracks in heterogeneous viscoelastic media that ultimately leads to failure of the component to perform its intended task. [ABSTRACT FROM AUTHOR]

Mechanically stable forms of lightweight materials with porosities up to 98% were first introduced in the form of silica aerogels in the 1930s. Recently, interest in aerogels and other lightweight materials in engineering applications have increased tremendously. Native silica aerogels are chemically inert, low-density, nanostructured porous materials with poor mechanical properties. They are the product of the sol-gel process whose final step involves extracting the pore-filled solvent with liquid carbon dioxide through supercritical drying. Practical applications of native aerogels are somewhat limited as they are brittle and hygroscopic, absorbing moisture from the environment which eventually leads to aerogel collapse due to capillary forces in the pores. Nevertheless, it has been recently discovered that crosslinking the nanoparticle building blocks of silica aerogels with polymeric tethers increases both modulus and strength significantly [4]. Along these lines, a novel, multifunctional, crosslinked silica aerogel, to be referred to as x-aerogel, is derived by coating and encapsulating the skeletal framework of amine-modified silica aerogels with polyurea as depicted in Fig. 10.1. [ABSTRACT FROM AUTHOR]

Polymer matrix composites (PMCs) used in aerospace high-temperature applications, such as turbine engines and engine-exhaust-washed structures, are known to have limited life due to environmental degradation. Predicting the extended service life of composite structures subjected to mechanical, high temperature, moisture, and corrosive conditions is challenging due to the complex physical, chemical, and thermomechanical mechanisms involved. Additionally, the constituent phases of the material, in particular the matrix phase, continuously evolve with aging time. It is the agingdependent evolution of the constituent properties that makes prediction of the long-term performance of PMCs in high-temperature environments so challenging. A comprehensive prediction methodology must deal with several complications presented by the highly coupled material aging, damage evolution, and thermooxidation processes. [ABSTRACT FROM AUTHOR]

This chapter presents nonlinear and time-dependent multiscale frameworks for the analysis of thick-section and multilayered composite materials and structures. Nested and hierarchical three-dimensional (3D) micromechanical models are formulated within the nonlinear analysis framework. The sublaminate model for a repeating ply-stacking sequence. A unified development of a class of constant deformation cell (CDC) micromodels is presented to generate the effective nonlinear response of a unidirectional lamina from the response of its matrix and fiber constituents (subcells). Two structural modeling approaches for nonlinear analysis of laminated composites are proposed using 3D and shell nonlinear finite element (FE) analysis. [ABSTRACT FROM AUTHOR]

Both fiber and particulate composite materials provide applications in materials science where the multiscale microstructure leads to the need for multiscale modeling. The length scales encountered range from the fiber and particle sizes whose dimensions are measured in microns, to the individual plies in laminates whose thicknesses are measured in fractions of millimeters, to the laminates themselves whose thicknesses in the laboratory are measured in millimeters, e.g., 40-50 mm. The laminates then form parts of composite structures whose sizes are measured in meters, although modeling at this scale will not form part of this chapter. While conventional composites are based on essentially homogeneous matrices, which can be polymeric, metallic, or ceramic, advanced composites are also being considered to have matrices, which are themselves composites reinforced by submicron particles or whiskers, e.g., carbon nanotubes. Such developments lead to the need to be able to estimate the properties of composite laminates that have multiscale reinforcements, e.g., fibers in particulate/whisker-reinforced matrices. Also, there is a need to predict the onset of damage in the materials when they are operating in service conditions. [ABSTRACT FROM AUTHOR]

Nanoscale metallic multilayered (NMM) composites represent an important class of advanced engineering materials which have a great promise for high performance that can be tailored for different applications. Traditionally, NMM composites are made of bimetallic systems produced by vapor or electrodeposition. Careful experiments by several groups have clearly demonstrated that such materials exhibit a combination of several superior mechanical properties: ultrahigh strength reaching 1/3 to 1/2 of the theoretical strength of any of the constituent materials [28], high ductility [25], morphological stability under high temperatures and after large deformation [22], enhanced fatigue resistance of an order of magnitude higher than the values typically reported for the bulk form [35], and improved irradiation damage resistance [17, 27], again, as compared to the bulk. However, the basic understanding of the behavior of those materials is not yet at a level that allows them to be harnessed and designed for engineering applications. [ABSTRACT FROM AUTHOR]

By formulating a continuum homogenization problem that includes inertia effects, a link is established between continuum homogenization and the estimation of effective mechanical properties for particle ensembles whose interactions are governed by potentials (e.g., as is seen in molecular dynamics). The focus of this chapter is on showing that there is a fundamental consistency of ideas between continuum mechanics and the study of discrete particle systems, and that it is possible to define a notion of effective stress applicable to discrete systems that can be claimed to have the same meaning as it has in continuum mechanics. [ABSTRACT FROM AUTHOR]

Composites have been used increasingly in various engineering applications which include, but are not limited to, the aerospace, automobile, sports, and leisure industries. To improve properties of composites so that they become stronger, stiffer, tougher, refractory, etc., it would be very useful to design the composite materials from the atomic levels. This requires proper multiscale and multilevel modeling techniques so that those techniques can be used for the design stage of new composites as well as the analysis of existing composites. This chapter presents multiscale and multilevel modeling techniques for different kinds of composite architectures which include particle-reinforced, fiber-reinforced, and woven fabric composites. [ABSTRACT FROM AUTHOR]

The past few decades have seen rapid developments in the science and technology of a variety of advanced heterogeneous materials like polymer, ceramic, or metal matrix composite, functionally graded materials, and porous materials, as well as various alloy systems. Many of these engineered materials are designed to possess optimal properties for different functions, e.g., low weight, high strength, superior energy absorption and dissipation, high impact and penetration resistance, superior crashworthiness, better structural durability, etc. Tailoring their microstructures and properties to yield high structural efficiency has enabled these materials to provide enabling mission capabilities, which has been a key factor in their successful deployment in the aerospace, automotive, electronics, defense, and other industries. [ABSTRACT FROM AUTHOR]

Fiber-reinforced composites can be engineered to exhibit high strength, high stiffness, and high toughness, and are, thus, attractive alternatives to monolithic polymer, metals, and ceramics in structural applications. To engineer the material for high performance, the relationship between material microstructure and its properties must be established to accurately predict the deformation and failure. Such a relationship between underlying constituent material properties and composite performance can also aid selection and/or optimization of new composite systems. Successful models can yield predictive insight into the origins of damage tolerance, size scaling, and reliability of existing composite systems and can be extended to investigate damage and failure under more complex loading and environmental conditions, such as fatigue and stress rupture. [ABSTRACT FROM AUTHOR]

The accumulated in last decades knowledge of fibre-reinforced composite materials, their effective properties as well as deformation and damage processes in them confirms a random (probabilistic) character of their failure (see, e.g. [1-4] and references therein). Such a character is determined by the specificity of microstructure of composites - a result of a manufacturing process of embedding of a huge number of reinforcing elements into a matrix. The resulting microscopic heterogeneity linked to randomness in positions of fibres, their bonding with the matrix, presence of microdefects, etc. causes a spatially and temporally non-uniform response to external loading even under macroscopically uniform loading conditions. The resulting pattern of deformation localisation and stress concentrations is neither uniform nor periodic; it defines macroscopic nonuniformity in evolution of various damage mechanisms. [ABSTRACT FROM AUTHOR]