Low-temperature thermal cycling of plasma sprayed zirconia coatings viacurvature measurements is used to quantify their nonlinear mechanicalbehavior. The nonlinear feature arises from the unique layered, porous andcracked morphology of thermal sprayed ceramic materials. With thisprocedure, various specimens were tested to investigate the effects ofprocessing condition. The measured nonlinear properties are interpreted inthe context of microstructural changes in the plasma sprayed coatings due todifferences in particle state upon impact and coating build-up. Theimplications of this study are significant for thermo-mechanical design ofstrain-tolerant ceramic coatings in thermal barrier applications.

Semiconductor strained layer superlattices are an ideal model material tostudy the effects of coherency strain in plasticity, due to the fine controlof nanolayer thickness and internal strain afforded by MBE deposition.Previously, nanoindentation of bulk InGaAs at 300K gave a yield pressure of6GPa (Jayawera et al Proc. Roy Soc, A459, 2049, 2003) while bending at 500centigrade gave a yield value of 30MPa (Pp’ ng et al Phil. Mag. 85, 4429,2005). In contrast, coherently strained InGaAs superlattices gavenanoindentation values of 3GPa at room temperature and bending at 500oC gavea yield value also around 3GPa. It appears that the coherency strain canimpart an athermal strengthening to the superlattice. It is clearlynecessary to do mechanical testing over the range 300-800K that will be ableto link the room temperature nanoindentation with the results from the hightemperature bending experiment and to determine the relationship betweenstrength, coherency strain and temperature. Preliminary experiments on thesesamples at elevated temperatures using a hot stage and the UMISnanoindentation system is difficult but feasible with the help of AFM toverify the contact area.

Glass transition temperature of polyetherimide (PEI) thin films andnanoporous PEI samples was investigated using differential scanningcalorimetry. In both of these systems, the glass transition temperaturedecreased with respect to the bulk value. In the nanoporous system, scanningelectron microscope images were used to characterize pore size distribution,and Monte Carlo simulations were performed to calculate the nearest neighborpore-to-pore distances. Pore-to-pore distances and thin film thicknessvalues were used to establish a quantitative analogy between thin films andnanoporous system.

This paper reports on the refinement of a mechanical model for theload-deflection of multilayer membranes under uniform differential pressureand on its application to the experimental extraction of materialparameters. Going beyond previous results, the analytical model takes intoaccount the mechanics of multilayers and elastic supports covering all casesbetween rigidly clamped to simply supported structures and enables thestraightforward assessment of stress profiles within the deformedstructures. A comprehensive set of long membranes made of variousmultilayers of silicon nitride and oxide films are fabricated andcharacterized. The out-of-plane deflection profile under pressure load ismonitored by means of a laser profilometer. The pressure is stepped up untilfracture occurs. From the stress profiles in the membrane at fracture, thebrittle material strength is analyzed using Weibull statistics. The bulgesetup has been fully automated for the measurement of 80 membranes perwafer. This realizes, for the first time, the high throughput-acquisition ofmechanical thin film data with convincing statistical control.

Our surrounding environment is teeming with useful energy, waiting to beharnessed (i.e., solar, wind, tidal, etc.). If this energy can be exploitedat the point where it is required, then the need to carry additional powersources can be reduced. In recent years, magnetic shape memory alloys (MSMA)have demonstrated an ability to convert mechanical energy to magneticenergy. Such conversions have lead to the investigation of these alloys forenergy harvesting applications.

There are a number of issues to address when forming a MSMA/polymercomposite. The polymer must be stiff enough to transmit the induced strainthrough the entire matrix, yet soft enough not to exceed the MSMA blockingstress. Also, the polymer must not dampen any force applied before it can betransmitted to the MSMA particles.

Ten polymers have been investigated for MSMA/polymer composites. The workpresented here will describe progress in nickel-manganese-gallium(Ni-Mn-Ga)/polymer composite fabrication and characterization. Specialattention will be given to polymer selection, optimizing particle dispersionand MSMA/polymer interfacial interactions.

Carbon in its various forms, specifically nanocrystalline diamond, maybecome a key material for the manufacturing of micro- andnano-electromechanical (M/NEMS) devices in the 21st Century. In order toutilize effectively these materials for M/NEMS applications, understandingof their microscopic structure and physical (mechanical properties, inparticular) become indispensable. The micro- and nanocrystalline diamondfilms were grown using hot-filament and microwave chemical vapor depositiontechniques involving novel CH4 / [TMB for boron doping and H2S for sulfurincorporation] in high hydrogen dilution chemistry. To investigate residualstress distribution and intermolecular forces at nanoscale, the films werecharacterized using Raman spectroscopy and atomic force microscopy in termsof topography, force curves and force volume imaging. Traditional forcecurve measures the force felt by the tip as it approaches and retracts froma point on the sample surface, while force volume is an array of forcecurves over an extended range of sample area. Moreover, detailed microscalestructural studies are able to demonstrate that the carbon bondingconfiguration (sp2 versus sp3 hybridization) and surface chemicaltermination in both the un-doped and doped diamond have a strong effect onnanoscale intermolecular forces. The preliminary information in the forcevolume measurement was decoupled from topographic data to offer new insightsinto the materials's

The wear resistance and the mechanical properties of polymer matrixcomposite fibers filled with inorganic fillers have been investigated inorder to find out the way to increase the wear resistance of the fiberswithout losing tensile modulus and strength. Nylon 6 and poly(ethyleneterephthalate) have been used as the matrix polymer and aluminum boratewhisker and carbon nanotube have been used as the fillers. The wearresistance of the fibers has been evaluated by observing the fiber crosssection after the side of the fiber was worn using a rotating drum coveredwith abrasive paper. The wear resistance of the nylon 6 and PET fibers wasincreased by the addition of these fillers without the loss of tensilemodulus and strength. The effects of the addition of the fillers on the wearresistance have been compared with the effects of stretching and heattreatment of the fibers.

Copper-based high strength nanofilamentary wires reinforced by bccnanofilaments (Nb or Ta) are prepared by severe plastic deformation for thewinding of high pulsed magnets. In-situ tensile tests under neutron beamwere performed on a Cu/Nb nanocomposite composed of a multiscale Cu matrixembedding 554 Nb filaments with a diameter of 267 nm and spacingof 45 nm. The evolution of elastic strains for individual lattice plane ineach phase and peak profiles in the copper matrix versus applied stressevidenced the co-deformation behavior with different elastic-plastic regimesand load sharing: the Cu matrix exhibits size effect in the finest channelswhile the Nb nanowhiskers remain elastic up to the macroscopic failure, witha strong load transfer from the copper matrix onto zones that are still inthe elastic regime. Taking into account results from residual latticestrains also determined by neutron diffraction, the yield stress in thefinest Cu channels is in agreement with calculations based on a singledislocation regime.

In this study, magnesium-aluminum (Mg-Al) based LDHs with different Mg2+/Al3+ ratios were prepared by co-precipitationmethod and modified with perfluorooctane-sulfonic acid tetraethylammoniumsalt (PFOSA). X-Ray Diffraction (XRD), Atomic Force Microscopy (AFM),Fourier Transfer Infrared spectroscopy (FTIR) and Thermogravimetric Analysis(TGA) were carried out to obtain the structural and thermal characteristicsof resulting materials. The organo-modified LDHs have been used in theformulation of Nafion® nanocomposites. Nanocomposite membranes were preparedby casting of LDH/PFOSA nanoparticles dispersed in Nafion® solution. Then,modified LDH/Nafion composite membranes were evaluated for water retentioncapability at ambient and elevated temperature.

In this work we present a micromechanical model for two-phaseductile/brittle laminates that captures the macroscopic behavior, as well asthe underlying micro-mechanisms of deformation and failure, in particularthe synergy between the inelastic deformation mechanisms of crazing andshear yielding. The finite element implementation of our model considers athree-dimensional representative volume element (RVE), and incorporatescontinuum-based physics-inspired descriptions of shear yielding and crazing,along with failure criteria for the ductile and brittle layers. Theinterface between the ductile and brittle layers is assumed to be perfectlybonded. The model successfully explains the volume fraction effect on themicro and macromechanics of ductile/brittle microlaminates subjected touniaxial tension.

In this study we evaluate the interfacial shear strength and scratchresistance of medical grade ultra-high molecular weight polyethylene(UHMWPE) (GUR 1050 resin) as a function of polymer crystallinity.Crystallinity was controlled by heating UHMWPE samples to a temperatureabove its melting point and varying the hold time and cooling rates. Degreeof crystallinity of the samples was evaluated using differential scanningcalorimetry (DSC). Quantitative nanoscale friction experiments wereconducted using an atomic force microscope with commercially available Si3N4 probes under dry conditions. A highercrystallinity resulted in lower friction force and lower interfacial shearstrength as well as increased scratch resistance. The trend in frictionresponse was observed in microscale friction measurements.

In this paper, we explore the use of nanoindentation techniques as a methodof measuring equivalent stress-strain curves of the PECVD SiOx thin films.Three indenter tips with different geometries were adopted in ourexperiments, enabling us to probe different regimes of plastic deformationin the PECVD SiOx thin films. A shear transformation zone (STZ) basedamorphous plasticity theory is applied to depict the underlying plasticdeformation mechanism.

Transparent conductive oxide (TCO) thin films are extensively used indisplay industry and they can be utilized for flexible displays. The polymerand the plastic materials used as flexible substrates are more bendable andlighter weight compared to glass substrates. However, its mechanical andsurface properties differed from glass substrates result in differentquality of TCO layers deposited on it. In this study, PolyethyleneTerephthalate (PET) and glass were used as substrates. Indium Tin Oxide(ITO), Zinc Oxide (ZnO), Mg-doped ZnO (MZO), Al-doped ZnO (AZO), Ga-dopedZnO (GZO), Al-doped MZO (AMZO), Ga-doped MZO (GMZO) were used as TCOmaterials deposited by RF sputtering. Rutherford Backscatter Spectroscopy(RBS) and X-Ray Diffraction (XRD) were used to analyze the chemicalcomposition and crystal structure of TCO thin films. Light transmittance andsurface resistivity were measured after the different deposited conditions., Mg-, Al-, Ga- doped ZnO indeed modified the optical properties of ZnO andbetter than ITO. However, the electrical conductivity was not improvedobviously compared to ITO when they deposited on PET substrate at roomtemperature.

The effects of several microstructural parameters on the mechanicalbehaviour of a helically perforated thin film structure, or inversemicrospring, were investigated using a finite element model[1]. Theparameters investigated were the helical pitch angle, the cross-sectionradius, and the coil spacing. The elastic modulus was found to depend moststrongly on the helical pitch angle (changing by a factor of 1.3 as thepitch angle went from 35° to 70°). Variations in the coil radius and thefilm thickness had a minor effect on the modulus. It was also found thatusing a finite size model (as opposed to an infinite model using periodicboundary conditions) produced better conditioned results. A preliminaryconfirmation of the model's validity was performed by comparison tonanoindentation results of a nickel helically perforated thin film.

Thermal spray is a significantly advanced but inherently complex depositionprocess that involves successive impingement of molten droplets on asubstrate to form coating with a ¡°brick-wall¡± layered structure. Theanisotropic microstructure of coatings is very sensitive to processingconditions and has significant influence on the properties. This study aimsto understand the processing-microstructure-thermal property correlation ofthermally sprayed coatings. Thermal transport properties of three coatingsystems forming composites with pores (yttria stabilized zirconia (YSZ)-Air), a second phase (Mo-Mo2C) and a graded material (YSZ-NiCrAlY) areinterpreted from the point of view of microstructure and chemicalcomposition. In the case of YSZ-Air composite, results indicate thatporosity contribution from 20-35% decreases the thermal conductivity by50-70% of the bulk value. For the intrinsic composite of Mo and Mo2C, whichcoexist as stable phases, thermal conductivity increases significantly with1.75wt% carbon addition since it reduces formation of MoO2 duringprocessing, but decreases with 3.5wt% carbon addition. This is attributed tolarger carbide retention in the latter. For the discrete layered and gradedcomposites of YSZ-NiCrAlY, which are made up of varying fractions of thesetwo constituents, thermal conductivity decreases sharply up to 40wt% YSZ andthen more gradually with increasing YSZ content. This paper examines theseexperimental findings by treating the these complex coatings as multiphasecomposites.