A study is made of top-surface cracks induced in brittle trilayers by cyclic indentation with a hard sphere in water. The trilayers consist of an external brittle layer (veneer) fused to an inner stiff and hard ceramic support layer (core), in turn adhesively bonded to a thick compliant base (substrate). These structures are meant to simulate essential aspects of dental crowns, but their applicability extends to a range of engineering coating systems. The study follows on from like studies of brittle monoliths and brittle-plate/soft-substrate bilayers. Competing fracture modes in the outer brittle layer remain the same as before: outer and inner cone cracks and radial cracks, all of which form in the near-contact zone and propagate downward toward the veneer/core interface. Inner cone cracks and radial cracks are especially dangerous because of their relatively steep descent through the outer layer as well as enhanced susceptibility to mechanical fatigue. Experiments are conducted on model glass/alumina/polycarbonate systems, using video cameras to record the fracture evolution in the transparent glass layer in situ during testing. Each fracture mode can lead to failure, depending on the maximum contact load and other variables (plate thickness, sphere radius). The potentially beneficial role of a stiff intervening core is discussed, along with potentially deleterious side effects of residual thermal-expansion-mismatch stresses.

An amorphous nanoparticulate aluminosilicate 3/2-mullite precursor has been synthesized and carefully characterized. The sol contained 2-nm particles of Q3(3Al) silica species together with six-coordinated alumina, which suggested an allophane-like structure of the nanoparticles. The sol remained stable for years, and formed an easily redispersible physical gel upon solvent evaporation. The gel crystallized to mullite at temperatures below 1000 °C, without going through any intermediate spinel phase. Thus, the nanoparticulate precursor is regarded as a homogeneous high-purity mullite precursor with a high Si–O–Al bond density, which is useful in the preparation of various nanostructured Al-rich aluminosilicate materials. The sols and gels were characterized by small-angle x-ray scattering, dynamic light scattering, x-ray diffraction, 27Al and 29Si magic-angle spinning (MAS) nuclear magnetic resonance spectroscopy, and differential thermal analysis.

The mechanical response of living tissue is important to understanding the injury-risk associated with impact events. Often, ballistic gelatin or synthetic materials are developed to serve as tissue surrogates in mechanical testing. Unfortunately, current materials are not optimal and present several experimental challenges. Bulk measurement techniques, such as compression and shear testing geometries, do not fully represent the stress states and rate of loading experienced in an actual impact event. Indentation testing induces deviatoric stress states as well as strain rates not typically available to bulk measurement equipment. In this work, a ballistic gelatin and two styrene-isoprene triblock copolymer gels are tested and compared using both macroscale and microscale measurements. A methodology is presented to conduct instrumented indentation experiments on materials with a modulus far below 1 MPa. The synthetic triblock copolymer gels were much easier to test than the ballistic gelatin. Compared to ballistic gelatin, both copolymer gels were found to have a greater degree of thermal stability. All of the materials exhibit strain-rate dependence, although the magnitude of dependence was a function of the loading rate and testing method.

The bonding strength of a carbon nanofiber array (CNFA) grown on a copper substrate is evaluated based on the measured shearing force-at-failure and the developed analytical stress model that enables one to determine the magnitude and the distribution of the interfacial shearing stress causing the measured (given) shearing force. The experiment is conducted using specially designed test specimens. A table version of the Instron tester is used to measure the applied force and the corresponding displacement in shear. The maximum predicted shear-off stress is about 300 psi (0.211 kgf/m2), and was determined, based on the developed stress model, as a product of the measured 5 kgf/m force at the interface failure and the computed parameter k = 0.0422 m–1 of the interfacial shearing stress.

Melamine (C3H6N6) was used as an additive for synthesizing aluminum nitride by combustion synthesis. It was found that at least 0.1 M of melamine addition to 1 M of aluminum and 0.8 MPa of nitrogen pressure were necessary to initiate a stable reaction. In addition to melamine, however, use of aluminum nitride as a diluent and application of forced nitrogen flow yielded better results. Analyzing the reaction temperatures, reaction rates, nitrogen contents, x-ray diffraction patterns, and scanning electron microscopy photographs, the optimum conditions for synthesizing AlN were established: (i) reactants were 90 wt% (1 M Al + 0.1 M melamine) + 10 wt% AlN diluent, (ii) chamber pressure was 0.9 MPa, and (iii) nitrogen flow rate was 15 l/min. Under these conditions, aluminum nitride with the stoichiometric nitrogen content of 34 wt% could be obtained.

We have used transmission electron microscopy to observe the structural changes that have occurred in multi-walled carbon nanotubes (MWCNTs) because of acid treatment. After a thiolation reaction of the acid-treated MWCNTs using P4S10 in refluxing toluene, we have also used electron energy loss spectroscopy to characterize the changes on the nanotubes from sidewall functionalization. We have determined that the sulfur content bonded to the nanotubes is 0.6% in terms of the atomic content of the samples. Raman spectroscopy was used to examine the vibrational changes that occurred to the nanotubes as well as identifying new vibrational modes around 500 cm−1 characteristic of carbon-sulfur bonds.

A new nonhydrolytic route for the preparation of well-crystallized size-tunable barium titanate (BaTiO3) nanocrystals capped with surface ligands is reported. Our approach involves: (i) synthesizing a “pseudo” bimetallic precursor, and (ii) combining the as-synthesized bimetallic precursor with a mixture of oleylamine with different surface coordinating ligands at 320 °C for crystallization and crystal growth. Different alcohols in the precursor synthesis and different carboxylic acids were used to study the effect of size and morphological control over the nanocrystals. Nanocrystals of barium titanate with diameters of 6–10 nm (capped with decanoic acid), 3–5 nm (capped with oleic acid), 10–20 nm (a nanoparticle and nanorod mixture capped with oleyl alcohol), and 2–3 nm (capped with oleyl alcohol) were synthesized, and can be easily dispersed into nonpolar solvents such as hexane or toluene. Techniques including x-ray diffraction, transmission electron microscopy, selected area electron diffraction, and high-resolution electron microscopy confirm the crystallinity and morphology of these as-synthesized nanocrystals.

The room temperature tensile properties of ultrafine-grained 25-μm gold wires were evaluated as a function of calcium (Ca) doping at various strain rates ranging between 10−3 and 10−1 s−1. Paradoxically, the increased amount of Ca was found to simultaneously increase the strength and ductility of the Au wires. However, based on scanning electron microscopy and tensile characterization, the grain size distributions, strain-hardening rate, and strain rate sensitivity of Au wires did not change with Ca, thus showing that neither grain refinement nor plastic instability are likely to be responsible for the concurrent improvement of strength and ductility.

Instrumented nanoindentation experiments, especially with sharp tips, are a well-established technique to measure the hardness and moduli values of a wide range of materials. However, and despite the fact that they can accurately delineate the onset of the elasto-plastic transition of solids, spherical nanoindentation experiments are less common. In this article we propose a technique in which we combine (i) the results of continuous stiffness measurements with spherical indenters – with radii of 1 μm and/or 13.5 μm, (ii) Hertzian theory, and (iii) Berkovich nanoindentations, to convert load/depth of indentation curves to their corresponding indentation stress–strain curves. We applied the technique to fused silica, aluminum, iron and single crystals of sapphire and ZnO. In all cases, the resulting indentation stress–strain curves obtained clearly showed the details of the elastic-to-plastic transition (i.e., the onset of yield, and, as important, the steady state hardness values that were comparable with the Vickers microhardness values obtained on the same surfaces). Furthermore, when both the 1 μm and 13.5 μm indenters were used on the same material, for the most part, the indentation stress–strain curves traced one trajectory. The method is versatile and can be used over a large range of moduli and hardness values.

This article reports conversion chemistry of preceramic polymer to ceramic phase during the fabrication of high-temperature stable silicon carbide and silicon carbonitride monolithic porous microchannels. The micromolding in capillariesmethod is used to fabricate porous channels by the initial infiltration of a solution of 1.5-μm diameter silica spheres or 1-μm diameter polystyrene spheres into polydimethylsiloxane channels followed by filling the void space among the spheres by using viscous commercial polymeric precursors. Subsequently, the polymer-sphere composite channel was cured and pyrolysed at 1200 °C under inert atmosphere, and final wet etching step of silica spheres with 10% hydrofluoric acid solution developed the pore structures by removing the silica spheres, whereas polystyrene sphere decomposes at the early stage of pyrolysis.

A semi-empirical interatomic potential formalism, the modified embedded atom method (MEAM), has been applied to obtain an interatomic potential for the Fe–Pt alloy system, based on the previously developed potentials for pure Fe and Pt. The potential can describe basic physical properties of the alloys (lattice parameter, bulk modulus, stability of individual phases, and order/disorder transformations), in good agreement with experimental information. The procedure for the determination of potential parameter values and comparisons between the present calculation and experimental data or high level calculation are presented. The applicability of the potential to atomistic studies to investigate structural evolution of Fe50Pt50 alloy thin films during post-annealing is also discussed.

Tin(II) organosilicophosphate glasses were prepared by nonaqueous acid–base reactions using orthophosphoric acid, dimethyldichlorosilane, and tin(II)chloride as the starting materials. The structure of the methylsiloxane-phosphate copolymer (methylsilicophosphate) and tin(II) methylsilicophosphate glasses was mainly investigated by the 31P nuclear magnetic resonance technique. A chain structure composed of the –(P–O–Si–O)m– silicophosphate bonds was found as the main structural unit in the methylsilicophosphate prepared by mixing orthophosphoric acid and dimethyldichlorosilane at room temperature. Tin(II) methylsilicophosphate glasses could be prepared by introducing SnCl2 as a cross-linking agent of silicophosphate chains. By increasing the reaction temperature, it was possible to promote the reaction and then to increase the network dimensions of the resultant tin(II) methylsilicophosphate glasses. It was found that the glasses with a high degree of condensation tend to have a better water durability in a humid atmosphere.

Surface evolution was studied for strained SrRuO3 films with a nominal 75 nm thickness deposited at various substrate temperatures (650–850 °C). Epitaxial growth of the films was achieved on single TiO2-terminated SrTiO3 (001) substrates by using ion-beam sputtering. The surface morphology of the deposited films was investigated by scanning tunneling microscopy in ambient conditions, and their microstructure was characterized by transmission electron microscopy. The self-organized step-terrace structure was observed for the films deposited at lower than 800 °C, suggesting that the epitaxial growth proceeded by step-flow growth. In particular, each film showed characteristic surface evolutions pertinent to the misfit strain relaxation stage, mostly influenced by the moving segment of misfit dislocations threading up to the surface: surface undulations for the film at the initial stage of relaxation (deposited at 650 °C), circular growth spirals during the relaxation stage (700 °C), and well-ordered step-terrace structure after almost full development of misfit dislocations (750 and 800 °C).

Cu46Zr47Al7 bulk metallic glass (BMG) and its composites in plate with different thicknesses up to 6 mm were prepared by copper mold casting. Primary crystallizing phases with different microstructures and volume fractions could be obtained under different cooling rates, forming some composites with different mechanical properties. Under compression tests, the 2-mm-thick monolithic BMG has a yield strength of 1894 MPa and a high fracture strength of up to 2250 MPa at plastic strain up to 6%, exhibiting apparent “work-hardening” behavior. The 4-mm-thick Cu46Zr47Al7 BMG composite containing martensite phase yields at 1733 MPa and finally fails at 1964 MPa with a plastic strain of 3.7%.

Stresses in thermally grown SiO2 films on silicon have traditionally been determined by substrate curvature measurements. This technique is useful for studying stresses in thin films, but it cannot be used to investigate stresses generated in the substrate during film growth. In the present work, we used microelectromechanical systems-based microstrain gauge devices fabricated from single-crystal and polycrystalline silicon (henceforth silicon and polysilicon, respectively) to measure oxidation-induced stresses in both dry and wet oxidizing ambients. Our microstrain gauges had thicknesses on the micrometer scale, and were themselves used as the substrates to be oxidized. Stresses could be detected in both the SiO2 scales and the silicon and polysilicon substrates. In the SiO2 scales, the stresses were compressive and exhibited viscoelastic relaxation. The as-grown compressive stresses were greater for wet oxidation than they were for dry oxidation, and greater in scales grown on polysilicon than they were in scales grown on silicon. The viscosity of thermally grown SiO2 was the same whether scales formed by wet or dry oxidation, and the same for oxide scales on silicon and polysilicon. Significant compressive stresses were also generated in polysilicon during oxidation, but not in silicon.

CdZnTe:In single crystals were annealed in CdZn vapors through a method involving a high-temperature step and a low-temperature step in sequence. The effects of annealing on the properties of CdZnTe:In were characterized with photoluminescence (PL) spectra. The neutral acceptor bound exciton (A0, X) peak, which was on the right shoulder of the neutral donor bound exciton (D0, X) peak, disappeared after annealing. A fine donor-acceptor pair structure and its longitudinal optical phonon replicas were clear before annealing. However, both of them became undistinguishable in the PL spectrum of annealed CdZnTe:In. The two phenomena imply that the annealing treatment can remove the impurities from CdZnTe:In wafers effectively. In addition, the intensity of Dcomplex band fell remarkably after annealing, which confirmed that Cd vacancies were well-compensated in the annealing treatment.

The yield strength of iron-carbon nanotube composites fabricated by in situ chemical vapor deposition of 2.2 vol% single-wall carbon nanotubes (SWNTs) inside an iron matrix showed substantial enhancement up to 45%, relative to that of similarly treated pure iron samples without carbon nanotubes of the same piece density. The work hardening coefficient and the Vickers hardness coefficient also significantly increased in these composites relative to the reference samples. X-ray diffraction together with energy dispersive x-ray measurements and micro-Raman spectroscopy indicated no concomitant formation of carbides and very little amorphous carbon during the vapor deposition process. Micro-Raman spectroscopy and scanning and transmission electron microscopy showed spectral signatures and images, respectively, indicating the formation and dispersion of SWNTs within the cavities of the iron matrix. It is suggested that the increased strength of the nanocomposites was due to the mechanical support provided to these cavities by the extremely strong SWNTs.

Fe element was partially substituted by Zr and Co in an attempt to enhance the glass-forming ability, and mechanical and soft magnetic properties of Fe74-xNb6B17Y3(Zr, Co)x (x = 3, 5, 8) amorphous alloys. Both partial replacements resulted in the enhancement of the glass-forming ability, and 3-mm diameter rods with a fully amorphous structure were prepared by a copper mold casting method. Zr and Co containing Fe-based bulk amorphous alloys exhibited high compressive fracture strength of about 4 and 3.5 GPa, respectively. However, Zr and Co induced different effects on the magnetic properties. Whereas the partial replacement of Fe by Zr was found to decrease dramatically the saturation magnetization, the partial replacement of Fe by Co provided an increase of about 25% of the saturation magnetization.

Investigations of bone mechanical properties are of major importance for bone pathology research, biomaterials, and development of in vivo bone characterization devices. Because of its complex multiscale structure, assessment of bone microstructure is an important step for understanding its mechanical behavior. In this study, we have investigated the strain rate influence on the mechanical properties of interstitial lamellae on two human femur bone samples. Nanoindentation tests were performed with the continuous stiffness measurement technique. Young's modulus and hardness were calculated using the Oliver and Pharr method. A statistical significant influence of strain rate on hardness was found (p < 0.05) showing a viscoplastic behavior of interstitial bone at the micrometer scale. This phenomenon may reflect the role of the organic component in the bone matrix mechanical behavior.

Joint reliability of immersion Ag with two different solders, Sn–37Pb and Sn–3.5Ag, were evaluated. We first compared the interfacial reactions of the two solder joints and also successfully revealed a connection between the interfacial reaction behavior and mechanical reliability. The Sn–Pb solder produced a Pb-rich phase along the interface between the solder and the Cu substrate during aging. In contrast, the Sn–Ag solder exhibits an off-eutectic reaction to produce the eutectic phase and Ag3Sn precipitate. The shear test results show that the Sn–Pb solder joint fractured along the interface showing brittle failure indications possibly due to the brittle Pb-rich layer. In contrast, the failure of Sn–Ag solder joint was only through the bulk solder, providing evidence that the interface is mechanically reliable. The results from this study confirm that the immersion Ag/Sn–Ag solder joint is mechanically robust, and thus the combination is a viable option for a Pb-free package system.