Low-temperature thermal cycling of plasma sprayed zirconia coatings via curvature measurements is used to quantify their nonlinear mechanical behavior. The nonlinear feature arises from the unique layered, porous and cracked morphology of thermal sprayed ceramic materials. With this procedure, various specimens were tested to investigate the effects of processing condition. The measured nonlinear properties are interpreted in the context of microstructural changes in the plasma sprayed coatings due to differences in particle state upon impact and coating build-up. The implications of this study are significant for thermo-mechanical design of strain-tolerant ceramic coatings in thermal barrier applications.

Semiconductor strained layer superlattices are an ideal model material to study the effects of coherency strain in plasticity, due to the fine control of nanolayer thickness and internal strain afforded by MBE deposition. Previously, nanoindentation of bulk InGaAs at 300K gave a yield pressure of 6GPa (Jayawera et al Proc. Roy Soc, A459, 2049, 2003) while bending at 500 centigrade gave a yield value of 30MPa (Pp’ ng et al Phil. Mag. 85, 4429, 2005). In contrast, coherently strained InGaAs superlattices gave nanoindentation values of 3GPa at room temperature and bending at 500oC gave a yield value also around 3GPa. It appears that the coherency strain can impart an athermal strengthening to the superlattice. It is clearly necessary to do mechanical testing over the range 300-800K that will be able to link the room temperature nanoindentation with the results from the high temperature bending experiment and to determine the relationship between strength, coherency strain and temperature. Preliminary experiments on these samples at elevated temperatures using a hot stage and the UMIS nanoindentation system is difficult but feasible with the help of AFM to verify the contact area.

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

This paper reports on the refinement of a mechanical model for the load-deflection of multilayer membranes under uniform differential pressure and on its application to the experimental extraction of material parameters. Going beyond previous results, the analytical model takes into account the mechanics of multilayers and elastic supports covering all cases between rigidly clamped to simply supported structures and enables the straightforward assessment of stress profiles within the deformed structures. A comprehensive set of long membranes made of various multilayers of silicon nitride and oxide films are fabricated and characterized. The out-of-plane deflection profile under pressure load is monitored by means of a laser profilometer. The pressure is stepped up until fracture occurs. From the stress profiles in the membrane at fracture, the brittle material strength is analyzed using Weibull statistics. The bulge setup has been fully automated for the measurement of 80 membranes per wafer. This realizes, for the first time, the high throughput-acquisition of mechanical thin film data with convincing statistical control.

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

There are a number of issues to address when forming a MSMA/polymer composite. The polymer must be stiff enough to transmit the induced strain through the entire matrix, yet soft enough not to exceed the MSMA blocking stress. Also, the polymer must not dampen any force applied before it can be transmitted to the MSMA particles.

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

Carbon in its various forms, specifically nanocrystalline diamond, may become a key material for the manufacturing of micro- and nano-electromechanical (M/NEMS) devices in the 21st Century. In order to utilize effectively these materials for M/NEMS applications, understanding of their microscopic structure and physical (mechanical properties, in particular) become indispensable. The micro- and nanocrystalline diamond films were grown using hot-filament and microwave chemical vapor deposition techniques involving novel CH4 / [TMB for boron doping and H2S for sulfur incorporation] in high hydrogen dilution chemistry. To investigate residual stress distribution and intermolecular forces at nanoscale, the films were characterized using Raman spectroscopy and atomic force microscopy in terms of topography, force curves and force volume imaging. Traditional force curve measures the force felt by the tip as it approaches and retracts from a point on the sample surface, while force volume is an array of force curves over an extended range of sample area. Moreover, detailed microscale structural studies are able to demonstrate that the carbon bonding configuration (sp2 versus sp3 hybridization) and surface chemical termination in both the un-doped and doped diamond have a strong effect on nanoscale intermolecular forces. The preliminary information in the force volume measurement was decoupled from topographic data to offer new insights into the materials's

The wear resistance and the mechanical properties of polymer matrix composite fibers filled with inorganic fillers have been investigated in order to find out the way to increase the wear resistance of the fibers without losing tensile modulus and strength. Nylon 6 and poly(ethylene terephthalate) have been used as the matrix polymer and aluminum borate whisker and carbon nanotube have been used as the fillers. The wear resistance of the fibers has been evaluated by observing the fiber cross section after the side of the fiber was worn using a rotating drum covered with abrasive paper. The wear resistance of the nylon 6 and PET fibers was increased by the addition of these fillers without the loss of tensile modulus and strength. The effects of the addition of the fillers on the wear resistance have been compared with the effects of stretching and heat treatment of the fibers.

Copper-based high strength nanofilamentary wires reinforced by bcc nanofilaments (Nb or Ta) are prepared by severe plastic deformation for the winding of high pulsed magnets. In-situ tensile tests under neutron beam were performed on a Cu/Nb nanocomposite composed of a multiscale Cu matrix embedding 554 Nb filaments with a diameter of 267 nm and spacing of 45 nm. The evolution of elastic strains for individual lattice plane in each phase and peak profiles in the copper matrix versus applied stress evidenced the co-deformation behavior with different elastic-plastic regimes and load sharing: the Cu matrix exhibits size effect in the finest channels while the Nb nanowhiskers remain elastic up to the macroscopic failure, with a strong load transfer from the copper matrix onto zones that are still in the elastic regime. Taking into account results from residual lattice strains also determined by neutron diffraction, the yield stress in the finest Cu channels is in agreement with calculations based on a single dislocation regime.

In this study, magnesium-aluminum (Mg-Al) based LDHs with different Mg2+/Al3+ ratios were prepared by co-precipitation method and modified with perfluorooctane-sulfonic acid tetraethylammonium salt (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 characteristics of resulting materials. The organo-modified LDHs have been used in the formulation of Nafion® nanocomposites. Nanocomposite membranes were prepared by casting of LDH/PFOSA nanoparticles dispersed in Nafion® solution. Then, modified LDH/Nafion composite membranes were evaluated for water retention capability at ambient and elevated temperature.

In this work we present a micromechanical model for two-phase ductile/brittle laminates that captures the macroscopic behavior, as well as the underlying micro-mechanisms of deformation and failure, in particular the synergy between the inelastic deformation mechanisms of crazing and shear yielding. The finite element implementation of our model considers a three-dimensional representative volume element (RVE), and incorporates continuum-based physics-inspired descriptions of shear yielding and crazing, along with failure criteria for the ductile and brittle layers. The interface between the ductile and brittle layers is assumed to be perfectly bonded. The model successfully explains the volume fraction effect on the micro and macromechanics of ductile/brittle microlaminates subjected to uniaxial tension.

In this study we evaluate the interfacial shear strength and scratch resistance 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 temperature above its melting point and varying the hold time and cooling rates. Degree of crystallinity of the samples was evaluated using differential scanning calorimetry (DSC). Quantitative nanoscale friction experiments were conducted using an atomic force microscope with commercially available Si3N4 probes under dry conditions. A higher crystallinity resulted in lower friction force and lower interfacial shear strength as well as increased scratch resistance. The trend in friction response was observed in microscale friction measurements.

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

Transparent conductive oxide (TCO) thin films are extensively used in display industry and they can be utilized for flexible displays. The polymer and the plastic materials used as flexible substrates are more bendable and lighter weight compared to glass substrates. However, its mechanical and surface properties differed from glass substrates result in different quality of TCO layers deposited on it. In this study, Polyethylene Terephthalate (PET) and glass were used as substrates. Indium Tin Oxide (ITO), Zinc Oxide (ZnO), Mg-doped ZnO (MZO), Al-doped ZnO (AZO), Ga-doped ZnO (GZO), Al-doped MZO (AMZO), Ga-doped MZO (GMZO) were used as TCO materials deposited by RF sputtering. Rutherford Backscatter Spectroscopy (RBS) and X-Ray Diffraction (XRD) were used to analyze the chemical composition and crystal structure of TCO thin films. Light transmittance and surface resistivity were measured after the different deposited conditions. , Mg-, Al-, Ga- doped ZnO indeed modified the optical properties of ZnO and better than ITO. However, the electrical conductivity was not improved obviously compared to ITO when they deposited on PET substrate at room temperature.

The effects of several microstructural parameters on the mechanical behaviour of a helically perforated thin film structure, or inverse microspring, were investigated using a finite element model[1]. The parameters investigated were the helical pitch angle, the cross-section radius, and the coil spacing. The elastic modulus was found to depend most strongly on the helical pitch angle (changing by a factor of 1.3 as the pitch angle went from 35° to 70°). Variations in the coil radius and the film thickness had a minor effect on the modulus. It was also found that using a finite size model (as opposed to an infinite model using periodic boundary conditions) produced better conditioned results. A preliminary confirmation of the model's validity was performed by comparison to nanoindentation results of a nickel helically perforated thin film.

Thermal spray is a significantly advanced but inherently complex deposition process that involves successive impingement of molten droplets on a substrate to form coating with a ¡°brick-wall¡± layered structure. The anisotropic microstructure of coatings is very sensitive to processing conditions and has significant influence on the properties. This study aims to understand the processing-microstructure-thermal property correlation of thermally sprayed coatings. Thermal transport properties of three coating systems forming composites with pores (yttria stabilized zirconia (YSZ) -Air), a second phase (Mo-Mo2C) and a graded material (YSZ-NiCrAlY) are interpreted from the point of view of microstructure and chemical composition. In the case of YSZ-Air composite, results indicate that porosity contribution from 20-35% decreases the thermal conductivity by 50-70% of the bulk value. For the intrinsic composite of Mo and Mo2C, which coexist as stable phases, thermal conductivity increases significantly with 1.75wt% carbon addition since it reduces formation of MoO2 during processing, but decreases with 3.5wt% carbon addition. This is attributed to larger carbide retention in the latter. For the discrete layered and graded composites of YSZ-NiCrAlY, which are made up of varying fractions of these two constituents, thermal conductivity decreases sharply up to 40wt% YSZ and then more gradually with increasing YSZ content. This paper examines these experimental findings by treating the these complex coatings as multiphase composites.