Commercial/military fixed-wing aircraft and rotorcraft engines often have to operate in significantly degraded environments consisting of sand, dust, ash, and other particulates. Marine gas turbine engines are subjected to salt spray, while the coal-burning industrial power generation turbines are subjected to fly ash. The presence of solid particles in the working fluid medium has an adverse effect on the durability of these engines as well as performance. Typical turbine blade damages include blade coating wear, sand glazing, calcia–magnesia–alumina–silicate (CMAS) attack, oxidation, and plugged cooling holes, all of which can cause rapid performance deterioration including loss of aircraft. This research represents the complex thermochemomechanical fluid structure interaction problem of semimolten particulate impingement and infiltration onto ceramic thermal barrier coatings (TBCs) into its canonical forms. The objective of this research work is to understand the underpinning interface science of interspersed graded ceramic/metal and ceramic/ceramic composites at the grain structure level for robust coatings and bulk material components for vehicle propulsion systems. This research enhances our understanding of the fundamental relationship between interface properties and the thermomechanical behavior in dissimilar materials for materials by design systems, and creates the ability to develop and fabricate materials with targeted macroscale properties as a function of their interfacial behavior. This project creates a framework to enable the engineered design of solid–solid and liquid–solid interfaces in dissimilar functionalized materials to establish a paradigm shift toward science from the traditional empiricism in engineering TBCs and high temperature highly loaded bulk materials. An integrated approach of modeling and simulation, characterization, fabrication, and validation to solve the fundamental questions of interface mechanisms which affect the properties of novel materials will be validated to guide component material solutions to visionary 2040+ military vehicle propulsion systems.

A new and unifying approach is presented for the analysis of plane-wave scattering by metal-strip gratings with a complex permittivity to account for their finite conductivity. A new set of metal modes is discovered, and the method of mode matching is employed for the formulation of the boundary-value problem. The effect of grating conductivity and thickness on the scattering characteristics are systematically examined, including the current distribution and power absorption within the metal strips. A. IntroductionGrating structures have been used for many applications ranging from microwave to optical frequencies[ 1-81. In particular, metal-strip gratings offer many advantages, such as easy fabrication and flexible design to achieve desired electromagnetic characteristics and good mechanical strength. In the past, metal-strip gratings have been often assumed to have an infinite conductivity and also to have a zero thickness, in order to simplify mathematical analyses[6-81. These simplifying assumptions may be justifiable at the microwave frequencies, but not at millimeter-wave frequencies and beyond.We present here a new and unifying approach to the class of metal-strip gratings which are realistically characterized by a finite conductivity and therefore must have a non-zero thickness. Specifically, the finite conductivity of metal is incorporated as the imaginary part of a complex dielectric constant, so that a metal-strip grating may be treated as a dielectric structure for which a rigorous formulation by the method of mode matching has been well developed [2,3]. Thus, the present approach is expected to yield accurate electromagnetic fjelds everywhere within a grating structure. The main purposes of this work are threefold: (1) to establish a theoretical foundation for the analysis of metal-strip gratings from a rigorous point of view, (2) to develop a clear physical picture of wave processes associated with metal-strip gratings, in order to gain a better physical understanding for design considerations, and (3) to evaluate accurately the effects of finite conductivity and finite thickness of the metal strips on the scattering characteristics of metal-strip grating, so that benchmark results can be established for a wide frequency range, as needed.In order to employ the method of mode matching for the analysis of metal-strip gratings, we have examined the modes in the grating layer, and have discovered a new set of modes, in addition to an old (or well-known) set, in the case of metal-strip gratings with a high conductivity. A mode in the new set has its energy confined mostly inside the metal strips, while a mode in the well-known set has its energy confined mostIy in the air spaces separating the metal strips. Therefore, the former is called a metal mode and the latter an air mode. Mathematically, it takes both sets, new and old, together to form a complete set of modes, so that the electromagnetic fields in the structure can be judiciously represented. Physically, since the metal modes are mostly confined ...

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In this paper, we present a rigorous analysis of current distribution induced on a metal-strip grating by an incident plane wave. The metal strips of the grating are characterized by a complex permittivity, with a large imaginary part to account for their finite conductivity. Such a scattering problem is formulated by the mode-matching method to determine the scattered fields everywhere, so that the volume distribution of current within a metal strip can be explicitly obtained. Numerical results are given to illustrate the effects of the dielectric constant of the surrounding media, as well as the incident angle and polarization on the current distribution induced by an incident plane wave. The air and metal modes form the basis for physical explanations of the numerical results obtained.

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