The present study develops a cohesive-shear-lag model to analyze the cycling stress-strain behavior of unidirectional fiber-reinforced ceramic matrix composites. The model, as a modification to a classical shear-lag model, takes into account matrix cracking, partial interfacial debonding, and partial breakage of fibers. The statistical nature of partial breakage of fibers is modeled by using a cohesive force law. The validity of the model is demonstrated by investigating stress-strain hysteresis loops of a unidirectional fiber-reinforced ceramic-glass matrix composite, SiC/1723. This example demonstrates the capability of the proposed model to characterize damage and deformation mechanisms of ceramic matrix composites under tension-tension cycling loading. The dominant progressive damage mechanism with cycling in this case is shown to be accumulation of fibers breakage, accompanied by increase in interfacial debonding and smoothening of frictional debonded interface.

Deposition of functional coatings for wear, corrosion and thermal resistance is a commonly employed process in many industries. Coatings are typically applied by spraying powders through a high temperature and high velocity gas jet. Powder particles are heated up and accelerated in the jet and they subsequently impact onto the surface to be coated. The two common means of depositing such coatings are high velocity oxy-fuel (HVOF) torches and plasma jets [1,2]. Typically, materials with lower melting points such as metallics are sprayed by HVOF systems whereas high melting point ceramic materials require higher temperature jets and they are applied using plasma torch systems. The HVOF systems produce combustion jets that can be supersonic at the jet exit (typically greater than kilometer per second velocities) and can reach gas temperatures up to 3000 K using pure oxygen as the oxidant. On the other hand, plasma jets can produce velocities and temperatures of the order of 10 2 m/s and 10 4 K respectively. Hence, these processes cover different velocity-temperature regimes for deposition of different types of coatings. While these processes are most commonly used in industry, another technique involves the use of detonation waves (i.e. supersonic premixed flames) for deposition of high density coatings [3–7]. The advantage of using detonation waves to deposit coatings stems from the fact that very high (supersonic) speeds can be sustained and thus this process provides the means to accelerate particles to very high velocities and produce dense coatings. However, the main disadvantage of this process is its discontinuous, repetitive nature. The detonation deposition process had originally been developed as a proprietary technology. Recently, a number of publications have appeared in this field such as references [6,7]. While the detonation process may have its practical limitations, it has the distinct advantage of enabling detailed, systematic study of particle deposition process since it subjects the particles to a well-characterized one dimensional flow field. Plasma and HVOF systems provide a turbulent flow field in which the injected powder particles are accelerated and heated up before impact. Description of particle properties and the control of the particle states (velocity and temperature) in a turbulent flow field are difficult at best. Experimentally, the measurements of particle temperatures and velocities are presented in a statistical form as probability density distributions of particle properties [10]. Computationally, particle properties are computed in a turbulent flow simulation by Lagrangian tracking of particles and developing statistics of particle properties [9] much like those determined experimentally. Because of the dispersion of particle states in a turbulent flow, a systematic study of coating properties as a function of particle processing conditions becomes difficult. In contrast, one dimensional uniform flow behind a detonation wave front subjects the particles to the same flow conditions, thus allowing examination of the deposition process as a function of particle parameters. Furthermore, flow and particle parameters can be computed in a relatively straightforward manner. Earlier work on detonation deposition of coatings have concentrated primarily on comparisons of this process with plasma processing in terms of the coating properties (hardness and wear resistance) and microstructure [3–6]. For example, Kharlamov has studied the relationship between adhesion strength of coatings and the parameters of detonation spraying and compared them with those for plasma spraying [4]. Saravanan et al [7] had performed a full Taguchi design of experiments to investigate the effects of detonation process parameters for alumina coatings. A similar study was conducted by Sundararajan et al [6] for tungsten carbide-cobalt, alumina and nickelchromium coatings. Their study concentrated on the tribological behavior of these coatings under different wear modes and compared both plasma and detonation generated coatings. Semenov and cetegen have recently discussed the deposition of nano-structured coatings by the detonation process [7]. One of the main objectives of this presentation is to use the detonation process to determine if highly nano-structured coatings can be generated with the detonation process that provides higher velocitylower temperature processing conditions compared to the plasma process. Secondly, a more basic understanding of the deposition process is sought using the detonation deposition without the turbulent, dispersive nature of the plasma and HVOF processes. In the following, we first describe the experimental systems used in this study and the features of both nano-structured and conventional alumina-titania coatings created by the detonation process. The effects of high particle kinetic energies, partition of the particle energies between thermal and kinetic and their influence on the deposition process also evaluated.

A three-dimensional, meso-electro-mechanical model has been formulated for description of PMN-PT-BT ceramics. Unlike the experimentally fit models and phenomenological models which are based on state variables and/or empirical relationships, this fully coupled, computational mesomechanics model for polycrystalline PMN-PT-BT ceramics is developed based on considerations of constitutive behavior of single crystals. Specifically, domain wall nucleation and evolution rate equations are proposed in this work to describe the nonlinear hysteresis behavior of these ceramics near the phase transition temperature with maximum permittivity.

Magnetically actuated diaphragm pumps were fabricated with low temperature co-fired ceramic (LTCC) tapes and Kapton polyimide film. The pumps consisted of a chamber machined in a LTCC substrate. The chamber was covered either on one or both sides with Kapton diaphragms on which copper coils were patterned. The diaphragms were actuated by passing electric current through the coils in the presence of permanent magnets. Passive Kapton flap valves were used to direct fluid flow into and out of the chamber. The first design consisted of a single, circular diaphragm pump. In the second design, two circular diaphragms were used. The two diaphragms are deflected into and out of the pressure chamber simultaneously. Flow rates of up to 7 mL/min were measured. The static response of a circular diaphragm subjected to magnetic forces was computed using the finite element method (FEM). The effect of the copper coils on diaphragm stiffness was accounted for. The design parameters (the number of windings and the size and location of the magnet) needed to maximize the volumetric displacement were determined. At relatively high currents, the coils heated up significantly and caused the pump’s performance to deteriorate.

Low Temperature Co-fired Ceramic (LTCC) tapes (DuPont, 951 series), originally developed for monolithic packaging of interconnects and hybrid microelectronic circuitry, have been used in the last four years to develop a meso-scale integrated fluidic technology. The LTCC fluidic technology is shown to be versatile, inexpensive, fast, and free of packaging problems. The manufacturing basis for this technology is patterning of individual tapes, which are laminated and co-fired to create a layered 3-D structure. In this paper, we present another attractive facet of this technology by creating 3-D shell structures with a single layer of LTCC tape. The processing technique is illustrated with hemispherical and cylindrical shells that have internal 3-D conduits. A novel three degree-of-freedom spherical stepper motor is also presented as an application of an active device using magneto-statically actuated curved LTCC shells.

This paper presents the design, fabrication and implementation of a novel off-chip hinge mechanism that can be latched in place to hold surface-micromachined structures off the edge of the chip. This mechanism was designed to enable fast, reliable, accurate, simple, and low-cost fabrication of advanced flip-chip MEMS structures. The upper layers of a flip-chip device can be commercially prefabricated on a host module attached to the hinge mechanism while the lower layers can be prefabricated on virtually any desired receiving module. This paper presents the design, fabrication and testing of a variety of advanced micromirror arrays assembled using this mechanism. This research demonstrates that structures comprised of several surface-micromachined layers can be positioned and bonded onto a variety of work surfaces such as ceramic substrates, MEMS chips and even CMOS electronics using adhesives, solder, gold bonding or mechanical latches. The hinge mechanism is designed to be easily disabled by a variety of methods should another bonding technique be desired. All flip-chip modules are designed with the mechanism to enable multiple flip-chip assembly options.

Tools for microfabrication on planar silicon substrates have led to remarkable advances in miniaturization of MEMS silicon devices. Silicon however has a limited functionality in many MEMS applications. Applications in which there are requirements for electrically or thermally insulating substrates, low capacitance, resistance to corrosion, or hermetic sealing limit some capabilities of silicon as a MEMS material. The introduction of packaging materials such as ceramics, polymers, and glass in MEMS fabrication makes it easy to fabricate 3-D meso or large-scale devices for a wide range of applications at cheaper cost. The application of these materials helps in constructing complex multilayer MEMS structures, which is one of the limitations of traditional Silicon MEMS devices. In this work we investigate and report laser micromachining of MEMS packaging materials such as ceramics and polymers for non-silicon MEMS device fabrication. A review of and general discussion is also presented in regard to the role of lasers in fabricating non-silicon MEMS devices. The experimental results of microstucturing these materials, SEM micrographs, surface morphology after machining, and their applications are reported.

Thermal actuator-based MEMS flaps with a length scale of 1,000 μm were developed for the enhancement of fluid mixing. These flaps were much larger than typical MEMS devices, and the experiment required an array of 10 flaps to be soldered onto a ceramic substrate with precision assembly. As a result, in the initial fabrication it was difficult to achieve good assembly yields capable of providing large deflections. To improve the yields and deflections, we have modified the flap design by reducing the size of solder pads, removing sharp corners, changing the number and the width of the actuator’s hot arms, and strengthening the support beams. In addition, we have developed a controllable process to reflow tin/lead solder on gold pads. Numerical simulations were used in the design process to assist in improving performance. The deflection was increased from 6.4 to 11.1 μm under a 5-V apply and the maximum von Mises stress reduced from 2000 to 500 Mpa. The simulated deflection-vs.-voltage relationship was verified by experimental characterizations.

The present study focuses on the evaluation of the laser-assisted machining (LAM) of pressureless sintered mullite ceramics. Due to mullite’s low thermal diffusivity and tensile strength, a new method for applying laser power is devised to eliminate cracking and fracture of the workpiece during laser heating. The LAM process is characterized by means of cutting force and surface temperature measurements for a variety of operating conditions. Estimated material removal temperatures and the ratio of the feed force to the main cutting force are used to determine material removal mechanisms and regimes for brittle fracture and semi-continuous and continuous chip formation. Surface roughness and subsurface damage are compared for typical parts produced by LAM and grinding. Tool wear characteristics are investigated for variations in laser power, and hence material removal temperature, during LAM of mullite with carbide tools.

High strain actuation can be obtained by engineering the crystallographic texture of piezoelectric ceramics. Single crystal piezoelectrics have significantly improved strain performance because crystal orientation can be controlled during use — their highly perfect lattice greatly simplifies the crystal orientation. Single crystals have properties significantly better than those of randomly oriented ceramics, but they are expensive and difficult to produce. Highly textured ceramics offer an alternative means of producing easily aligned crystals, as the majority of the crystallites in the ceramic share a common crystallographic orientation. Textured piezoelectric ceramics are expected to provide improved properties compared to untextured ceramics, with lower processing costs than single crystals. NexTech Materials is developing textured piezoelectrics in PMN-PT system via Templated Grain Growth (TGG). In the TGG process, anisotropic template particles are oriented in a fine particle matrix in the green state. During heat treatment, the crystals consume the surrounding matrix, resulting in a textured polycrystal. A TGG system requires both matrix and template particles. The matrix must provide significant driving force for densification and grain growth. Templates must be large, anisotropic, and crystallographically isostructural with the matrix material. Anisotropic template shape is difficult to achieve in perovskite-based piezoelectrics, which have highly symmetric (cubic) crystal structures at their processing temperature. In addition, the matrix environment often contains highly corrosive lead based liquid phases that make chemical stability difficult to achieve. Characterization of textured samples involves texture evaluation and phase analysis via XRD, and SEM analysis of template growth and chemical stability as well as piezoelectric performance measurement The development and characterization of the TGG components and their integration will be discussed.

It is a common practice in the oil and gas industry to improve well production by creating hydraulic fractures in petroleum bearing formations. In order to maintain the fracture open in the formation as a flow path for oil and gas production, it is generally created by injecting a viscous fluid mixed with propping materials such sands or ceramic particles, which are all called proppants. It is very important to have a precise knowledge of the temperature profiles both in the wellbore and in the fracture because temperature affects gel loading (required polymer concentration in the fluid), fluid rheology, the ability for the fluid to carry proppants, and the condition for the gelled fluid to break down after the operation. Several models have been developed in the literature to predict wellbore and fracture temperature profiles, and most of them are analytical. Since an analytical solution cannot handle variable fluid and rock properties and variable pumping rates, a unique numerical scheme is developed in this study to solve the PDE’s that govern the heat transfer both in the wellbore and in the fracture, and the surrounding earth. Since the coordinate system for temperature calculations in the wellbore is different from that in the fracture, two heat transfer models are coupled together to solve the entire problem. In addition to the effects of convective and conductive heat transfer in the well and the fracture, the models also rigorously consider fluid flow and heat transfer in the porous formation surrounding the well and the fracture. The models were first verified by analytical results for constant flowrate injection. One can easily measure the wellbore temperature at any location by running a temperature gauge inside the well, but no one has directly measured with the current technology the fluid temperature profile inside a narrow hydraulic fracture (which is usually less than one inch in width at the wellbore) far beyond the wellbore limit. In this study, the following temperature survey data were used to infer the fluid temperature inside a fracture: A temperature gauge was run into a well and was set inside the wellbore at the location where the hydraulic fracture was anticipated to be created outside the wellbore; and the well was put into production (or flowback) immediately after the hydraulic fracturing operation. Within a couple of minutes during the flowback, the fluid passing through the temperature gauge was actually from inside the fracture. The models were then verified by the actual temperature survey data during pumping and flowback. The heat transfer models were finally integrated into a hydraulic fracture design simulator that is widely used in the oil and gas industry. The numerical scheme developed to solve the models in this study has been implemented in such a way that it is not only accurate for calculating the temperature profiles, but that it also runs fast for real-time analysis and monitoring during the hydraulic fracturing operations. To authors’ knowledge, it is the first attempt in the literature to verify a heat transfer model for hydraulic fracturing using actual measured data inferred from the temperature of the fluid flowed back from inside a created hydraulic fracture.

In many plasma-aided manufacturing systems, metallic or ceramic particles are introduced in a thermal plasma. The heat transfer from the plasma to the particle, in part, governs the quality of the products. To design thermal plasma-aided manufacturing systems and to predict their performance, accurate determination of particle heat transfer is necessary. In this paper, a spherical particle introduced in an ionized gas made up of electrons, ions, and neutrals is considered. A model to accurately determine heat transfer to the particle is developed.

This paper presents the technique of high precision microscale laser bending and the study of the thermomechanical phenomena involved. The use of pulsed and CW lasers for microscale bending of ceramics, silicon, and stainless steel is demonstrated. Experimental studies are conducted to find out the relation between bending angles and laser operation parameters. Bending results obtained by a pulsed and a CW laser are compared. Changes of surface composition after laser irradiation are analyzed. Numerical calculations based on thermo-elasto-plastic theory are conducted and results are compared with the experimental data Examples of industrial applications of high precision laser bending are given.

A detailed thermal analysis for the FSOI (Free Space Optical Interconnect) technology incorporating VCSEL (Vertical Cavity Surface Emitting Laser) devices is performed using commercially available software. FSOI is one of the latest technologies used to transmit information at high-speed to/from a microprocessor to memory device via photons. Due to large heat dissipation and compact packaging design, temperature and associated thermal strain/stress could reach high values in the FSOI assembly, causing serious reliability and quality problems. Several design options are investigated in order to provide optimal thermal management for the FSOI module, and maintain VCSEL temperatures within reasonable limits. Convective cooling results for both organic and ceramic boards are investigated. For designs with organic boards and without any thermal enhancement, the VCSEL temperature is well above the acceptable limit of 85°C at an ambient temperature of 30°C. The sequential inclusion of pedestals, board thermal vias, conductive rings between the optical modules, and metallic (Al) rods will significantly enhance the module thermal performance and reduce VCSEL temperature to 46°C. The presence of thermal vias in the organic board is critical; however, if the copper area percentage in the via block vs. the die area is above 3%, the VCSEL temperatures will remain constant. The ceramic boards provide a good thermal solution, as VCSEL temperatures remain below the upper limit without including any thermal vias in the board. The comparison between the effect of convective air speed on FSOI with ceramic versus organic boards reveals that the VCSEL temperature is slightly higher (less than 2°C) for the case incorporating a ceramic board. However, the ceramic board has no thermal vias, compared to the 100% copper via block in the organic board. Hence, the same results are accomplished with much less complexity in the ceramic substrate design alternative. This option is suggested for manufacturing purposes, with improved thermal performances.

Transient heat transfer behavior from a horizontally confined ceramic-based MCM disk with jet impingement has been systematically explored. The relevant parameters influencing heat transfer performance are the steady-state Grashof number, jet Reynolds number, and ratio of jet separation distance to nozzle diameter. In addition, an effective time, t on , representing a certain transient time when the mixed convection effect due to jet impingement and buoyancy becomes significant relative to heat conduction, is introduced. Both the transient chip and average Nusselt numbers on the MCM disk surface decrease with time in a very beginning period of 0 ≤ t < t on , whereas it gradually increases or keeps constant with time and finally approaches the steady-state value in the period of t on ≤ t < t s . As compared with the steady-state results, if the transient chip and average heat transfer behaviors may be considered as a superposition of a series of quasi-steady states, the transient chip and average Nusselt numbers in all the present transient experiments can be properly predicted by the existing steady-state correlations when t ≥ 4 min in the power-on transient period.

The mechanical properties of silicon nitride (Si 3 N 4 ) ceramics are determined by their microstructure, which in turn depends on processing routes adopted to fabricate the material. To obtain dense Si 3 N 4 , sintering aids are almost always added during the densification process. The sintering aids remain in the ceramics as amorphous residues which adversely affect the high temperature mechanical behavior of the material. In this paper, we have investigated the effects of processing on the mechanical behavior of a sintered Si 3 N 4 ceramic through detailed microstructural observations. A commercial Si 3 N 4 was annealed using conventional furnace annealing and microwave annealing at different temperatures. Creep tests were performed to compare the high temperature mechanical behavior of the as-sintered and annealed ceramics. It was found that microwave and furnace annealing heat-treatments improve the creep resistance of the ceramic through devitrification of the triple junctions phases.

This paper provides a review of recent studies undertaken to examine the mechanical and thermal stability of silicon nitride ceramic components that are currently being considered for use in gas turbine applications. Specific components examined included a bowed ceramic nozzle evaluated in an engine test stand, ceramic vanes exposed in two field tests, and an air-cooled vane that is currently under development. Scanning electron microscopy was used to elucidate the changes in the microstructures arising from the environmental effects. The recession of the airfoils resulting from the volatilization of the normally protective silica layer was also measured. The stability of the intergranular phases was evaluated using x-ray diffraction. The surface strength was measured using a miniature biaxial test specimen, which was prepared by diamond core drilling.

Diamond, diamond-like, and their composites (with TiC, TiN, and AlN for diamond, and Cu, Ag, Ti, and Si for diamondlike carbon) have extremely desirable chemical, electrical, and mechanical properties. These corrosion- and erosion-resistant coatings have a wide variety of applications, ranging from biomedical device coatings to packaging of microelectronic devices. However, many of these applications are limited by the poor adhesion of these films to metals, ceramics, and polymers. The adhesion of a film is determined primarily by internal stresses in the film, thermal and lattice mismatch, and most importantly by interfacial bonding. We have developed methods based on mechanical interlocking, chemical bonding, grading of interatomic potentials, and the multilayer discontinuous thin films approach to control stresses and strains in thin films. A substantial improvement in adhesion and wear properties is obtained by using these methods selectively. We review issues related to the adhesion of diamond, diamond-like carbon, and composite films on metal, polymeric, and ceramic substrates.

There is a great deal interest in minimizing thermal and residual stresses at the interfaces of metals and ceramics. These stresses develop because of the large mismatch in thermally induced strains that exists between these two materials. The differences are significant enough to cause premature component failure in a variety of applications, including thermal barrier coatings (TBCs) for turbine blades and ceramic coatings for cutting tools. One approach to minimizing these stresses involves functionally grading the material distribution at the metal-ceramic interface. A significant amount of effort has been focused on the development of functionally graded nickel-alumina composites as a model system to determine the architectural features of the material gradient that will minimize these stresses. This effort has led to the development of an experimentally verified modeling approach based on thermomechanical, elastoplastic finite element analysis that can be used to predict the stress distributions in functionally graded metal-ceramic composite materials. This approach has been coupled with a mathematical optimization technique, known as a Genetic Algorithm (GA), to determine the optimal architecture for minimizing thermal and residual stresses at metal-ceramic interfaces.

Three working-liquid charging methods for miniature heat pipes are introduced, and their advantages and disadvantages are described. Using these methods, two types of ceramic heat pipes were charged and tested. The ceramic heat pipes were made of alumina and have overall dimensions of 89 mm × 12 mm × 2.9 mm and a designed vapor space of 82.5 mm × 4.1 mm × 1.27 mm. Axial micro capillary grooves were provided on the top and bottom or sidewalk inside the heat pipes as wick structures. Water was used as working liquid. More than 20 Watts of heat input was achieved on a 5 mm × 5 mm heating surface. The corresponding heat flux was 80 W/cm 2 .