Mechanical analog of temperature for the description of force distribution in static granular packings

The mechanical analog of temperature for the description of force distribution in static granular packings was discussed. The constraint on entropy was found to be considered as measure of the degree of retained disorderness in the system. The role of mechanical temperature as a parameter controlling the mixity between energy minimization and entropy maximization in the equilibrium condition was also elaborated.published_or_final_versio

Nanomechanical Characterization of Soft Materials

This chapter reviews the creep or viscoelastic deformation behavior of soft materials under nanoindentation-type testing. Analysis protocols of nanoindentation based on the Hertzian elastic contact theory, linear viscoelasticity analyses, and a more recent rate-jump method, are described and assessed. In addition to continuous viscoelasticity, a special type of discrete creep deformation, often observed in a wide range of materials during nanomechanical testing, is also highlighted.postprin

The effects of creep on elastic modulus measurement using nanoindentation

During the unloading segment of nanoindentation, time dependent displacement (TDD) accompanies elastic deformation. Consequently the modulus calculated by the Oliver-Pharr scheme can be overestimated. In this paper we present evidences for the influence of the measured modulus by TDD. A modification method is also presented to correct for the effects of TDD by extrapolating the TDD law in the holding process to the beginning of the unloading process. Using this method, the appropriate holding time and unloading rate can be estimated for nanoindentation test to minimise the effects of TDD. The elastic moduli of three materials computed by the modification method are compared with the results without considering the TDD effects.published_or_final_versio

A rate-jump method for characterization of soft tissues using nanoindentation techniques

The biomechanical properties of soft tissues play an important role in their normal physiological and physical function, and may possibly relate to certain diseases. The advent of nanomechanical testing techniques, such as atomic force microscopy (AFM), nano-indentation and optical tweezers, enables the nano/micro-mechanical properties of soft tissues to be investigated, but in spite of the fact that biological tissues are highly viscoelastic, traditional elastic contact theory has been routinely used to analyze experimental data. In this article, a novel rate-jump protocol for treating viscoelasticity in nanomechanical data analysis is described. © 2012 The Royal Society of Chemistry.postprin

Effects of pore-channel ordering on the mechanical properties of anodic aluminum oxide nano-honeycombs

The mechanical properties of anodic aluminum oxide (AAO) nano-honeycombs with different spatial ordering of pore-channels are investigated by nanoindentation. The pore-channel ordering is systematically varied by carefully adjusting the orientation of the aluminum used for anodization. The results indicate that the strength of AAO structures increases significantly with the regularity of their pore-channel arrangement, whereas the elastic modulus is less sensitive to pore-channel regularity. © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.postprin

The sintering and densification behaviour of many copper nanoparticles: A molecular dynamics study

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Size effect on the strength of micron-sized polycrystals – A dislocation dynamics simulation study

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Effects of boron doping on the grain growth behaviour of γ/γ nickel-aluminium alloy

Effects of 0.5 at. 9c boron doping on Nigs Al y/f superalloys were investigated for the first !ime. yielding a number of observations not previously observed in the literature. First, the grant growth kinetics of both the doped and undoped alloys were found to disobey the simple Nielsen law d = Of. but instead follow an equation of the type d = C ln(r) + C0. The constants C and Co were found to be respectively 10.2 and 23.2 for the boron-free alloy, and 6.2 and 14.2 for ire boron-doped alloy, i.e., the grain growth rate was retarded significantly upon boron doping. Such a retarding effect is thought to be due to the formation of a boron-nickel cosegregated zone observed at the grain boundaries of the doped alloy: the width of the zone, in juni's, is two to three orders of magnitude larger than the boron induced disordered layer found in nickel rich Ni3Al. compounds doped with boron. Other associated effects of the cosegregated zone include a -harp increase in toughness, much better slip transmission across grains and reduced workhardening rates. Another intriguing point is that the Y precipitates were found to segregate to the grain boundaries in the boron-free alloy after cold rolling, but no such segregation of y precipitates, has been observed in the boron-doped alloy. The different deformation microstructures and the retarded grain growth rates upon boron doping will be discussed.published_or_final_versionlink_to_subscribed_fulltex

Additive free co-deposition of nanocrystalline copper/cuprous oxide by electrodeposition

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Metal-to-insulator transition in sputter deposited 3Ni/Al thin films

Thin films with a 3Ni/1Al atomic ratio were synthesized using low-power dc planar magnetron sputtering from a nickel–aluminum alloy target. Chemical analysis revealed that a significant amount of oxygen was incorporated into the Ni–Al thin films which were prepared under a typical vacuum of ~1×10–5 mbar. These thin films were found to exhibit a prominent temperature dependence of electrical resistance, the magnitude of which diminishes upon increasing the film thickness or the in situ deposition temperature. Cross-sectional transmission electron microscopy revealed a nanocrystalline structure of the films which changes as a function of deposition temperature. Electron diffraction indicates the existence of a single-phase face-centered cubic structure in the nanocrystallites, yet with an enormous expansion of the crystal lattice for the low temperature deposited films when compared with the intermetallic Ni3Al lattice. On raising the deposition temperature or increasing the film thickness, however, the lattice constant gradually declines toward the lattice constant of bulk Ni3Al. An attempt is made to correlate the lattice structures of the crystallites and the electrical properties of the films with the potential influence of the dissolved oxygen in the Ni–Al lattice. © 2000 American Institute of Physics.published_or_final_versio