Effect Of Mechanical Deformation Research Articles

Effect of mechanical deformation on the critical current in YBa2Cu3O7−b superconducting films

It is shown that local mechanical bending of YBa2Cu3O7−b Ag-coated superconducting films deposited on flexible metal substrates in the temperature interval 77–300 K may increase the critical density Jc of the transport current to values as high as 106 A/cm2 or even higher at 77 K. Also, bending decreases the voltage criterion. This means a rise in the intergranular conductivity and, accordingly, a reduction of Joule losses.

The coupled effects of mechanical deformation and electronic properties in carbon nanotubes

Coupled effects of mechanical and electronic behavior in single walled carbon nanotubes are investigated by using quantum mechanics and quantum molecular dynamics. It is found that external applied electric fields can cause charge polarization and significant geometric deformation in metallic and semi-metallic carbon nanotubes. The electric induced axial tension ratio can be up to 10% in the armchair tube and 8.5% in the zigzag tube. Pure external applied load has little effect on charge distribution, but indeed influences the energy gap. Tensile load leads to a narrower energy gap and compressive load increases the gap. When the CNT is tensioned under an external electric field, the effect of mechanical load on the electronic structures of the CNT becomes significant, and the applied electric field may reduce the critical mechanical tension load remarkably. Size effects are also discussed.

Effects of mechanical deformation and annealing on the microstructure and hardness of Pb-free solders

The microstructure property relations of several Pb-free solders are investigated to understand the microstructural changes during thermal and mechanical processes of Pb-free solders. The Pb-free solder alloys investigated include pure Sn, Sn-0.7% Cu, Sn-3.5% Ag, and Sn-3.8% Ag-0.7% Cu (in weight percent). To reproduce a typical microstructure observed in solder joints, the cooling rate, ingot size, and reflow conditions of cast alloys were carefully controlled. The cast-alloy pellets are subjected to compressive deformation up to 50% and annealing at 150°C for 48 h. The microstructure of Pb-free solders is evaluated as a function of alloy composition, plastic deformation, and annealing. The changes in mechanical property are measured by a microhardness test. The work hardening in Sn-based alloys is found to increase as the amount of alloying elements and/or deformation increases. The changes in microhardness upon deformation and annealing are correlated with the microstructural changes, such as recrystallization or grain growth, in Pb-free solder alloys.

The influence of mechanical deformation on the electrical properties of single wall carbon nanotubes

Recent experimental studies and atomistic simulations have shown that carbon nanotubes (CNTs) display strong interplay between the mechanical deformation and electrical properties. We have developed a simple and accurate method to determine atom positions in a uniformly deformed CNT via a continuum analysis based on the interatomic potential. A shift vector is introduced to ensure the equilibrium of atoms. Such an approach, involving only three variables for the entire CNT, agrees very well with the molecular mechanics calculations. We then study the effect of mechanical deformation on the band gap change of single wall CNTs under tension, torsion, and combined tension/torsion via the k-space tight-binding method. Prior studies without this shift vector lead to significant overestimation of the band gap change. It is established that the conducting CNTs may easily become semi-conducting ones subject to mechanical deformation, but the semi-conducting CNTs never become conducting ones upon deformation.

Two-Phase (Air and Water) Flow through Rock Joints: Analytical and Experimental Study

This research deals with the characterization of 2-phase flow in a fractured rock mass. A comprehensive mathematical model with which to predict the quantity of each flow component in a single joint is developed. A joint with 2 parallel walls filled with layers of water and air (stratified) is analyzed. The effects of mechanical deformation of the joint, compressibility of fluids, the solubility of air in water, and phase change between fluids have been taken into account to develop analytical expressions that describe the behavior at the airwater interface. The model was calibrated using a newly designed 2-phase triaxial cell. Tests were conducted on fractured hard rock samples for different confining pressures with inlet water and inlet air pressures. As in single-phase flow, it was found both experimentally and theoretically, that the flow quantities of each phase decreases considerably with an increase in confining stress. Results also confirm that the effect of joint deformation and compressibility of fluids governs the flow volume of 2-phase flow. Good agreement was obtained between experimental data and numerical predictions.

Theoretical Prescriptions for Improving Conductances of Short DNA Segments Sandwiched between Metal Electrodes

In the band-resonant tunneling regime, we studied by theoretical simulations the effects of mechanical deformation and gate modulation on the electronic transport properties through short (34 Å-long) deoxyribonucleic acid (DNA) segments sandwiched between two aluminum electrodes. We found that the structural deformation of DNA, such as the tilting of the guanine (G)–cytosine (C) base pairs, causes the upper shifts of their occupied energy levels. When these energy levels cross the Fermi level and the excess charge flows out to the electrodes, the hole is injected into the G–C base pairs, dominantly into the guanine array. In addition, we found that by applying the negative gate bias voltages, the occupied energy levels are raised across the Fermi level and the hole is injected into the guanine array. By these carrier injections, the conductances of the short DNA molecule improve dramatically in both cases.

Role of mechanical deformation in the texturing of coated conductor composites

Ni and Ni-based alloys have received considerable attention as the substrates for HTS coated conductors. A critical step in the successful fabrication of coated conductor composites on metal substrates is to produce cube texture by mechanical deformation using the rolling assisted biaxial textured substrate (RABiTS) approach. In this paper, we investigated the effects of mechanical deformation and heat treatment on the growth of texture in nickel and nickel–tungsten alloys with the objective of understanding mechanisms of mechanical texturing in coated conductor substrates. The results show that the sharpest cube texture is obtained by cold rolling nickel and nickel tungsten alloys in passes of less than 5% deformation followed by annealing at high temperature.

Mechanical deformation effect on CsI(Tl) scintillators efficiency

Due to the technological limitations in scintillation crystal growth and machining afterwards, crystals always contain certain internal defects and nonuniform distribution of intrinsic stresses. This work is directed to study the effect of CsI(Tl) mechanical deformation on their scintillation efficiency. It is shown that light output changes depend on the type of deformation (shock, steady deformation) and crystallographic orientation of specimen. The value of the phenomenon reaches up to 20% of the CsI(Tl) light output. Stress relaxation is the reason for the scintillator light output recovery. For CsI(Tl) scintillator mechanical deformation effects on light output will significantly decrease in the first 7–10 days after application of the stress and might completely disappear within 30–40 days.

Development of a technique for modelling clay liner desiccation

AbstractThis paper presents a model for the analysis of clay liner desiccation in a landfill barrier system due to temperature effects. The model incorporates consideration of fully coupled heat‐moisture‐air flow, a non‐linear constitutive relationship, the dependence of void ratio and volumetric water content on stress, capillary pressure and temperature, and the effect of mechanical deformation on all governing equations. Mass conservative numerical schemes are proposed to improve the accuracy of the finite element solution to the governing equations. The application of the model is then demonstrated by examining three test problems, including isothermal infiltration, heat conduction and non‐isothermal water and heat transport. Comparisons are made with results from literature, and good agreement is observed. Copyright © 2003 John Wiley & Sons, Ltd.

Effect of Mechanical Deformation on Permeation of Hydrogen in Iron

Rate of hydrogen permeation was measured under static as well as dynamic mechanical deformation conditions. Cylindrical tensile test specimens were used for the study and hydrogen permeation was measured electrochemically. It was observed that the hydrogen diffusivity decreased as plastic deformation increased for the static deformation experiments while elastic deformation had no significant effect on diffusivity but increased the steady state permeation flux. For the dynamic loading experiment, an elastic deformation increased the hydrogen permeation rate almost linearly. Onset of plastic deformation led a sudden decrease of permeation rate and the reduced rate was rapidly recovered when the plastic deformation ceased. These rapid changes in the permeation rates were explained that the absorbed hydrogen was trapped by dislocations and creation rate and density of dislocations changed drastically when plastic deformation started and stopped.

SANS studies of hybrid nanosystems

The soft matter group of LLB is centered on Small Angle Neutron Scattering (SANS). It is in charge of three classical SANS facilities (one annular detector and two XY detectors) and one polarized neutron SANS, and is developing a new USANS diffractometer. The group is also connected withneutron reflectivity, and to a lesser extent to inelastic scattering (spin echo, time of flight). In the field of soft matter, the expertise has been for many years focused on polymer solutions (neutral and charged), adsorbed polymers, polymer melts, and liquid crystalline polymers, witha focus on the effect of mechanical deformation (“rheo-SANS”). More recently, such deformation effects have been studied also on polymer latex films and latex-silica composites. We have chosento present this work here, which is at the boundary between polymer and colloid science, since interactions between silica particles in the films are involved and control partly the reinforcement of the polymer film. We will balance this example with another, the case of particles dispersed inside aqueous clays gels: Here, the particles are magnetic and play the role of probes, notinfluencing the properties of the material, but allowing an understanding of its properties, in particular the mechanical ones. Both systems are hybrid materials for which SANS is useful. For maghemite-clay mixtures, the contrast-matching method with a mixture of normal and deuterated water allows one to separate the different correlations: As usual, SANS is a powerful tool for thestudy of ternary systems. For composite films, the case of silica particles covered by polymer is under development; in this situation, labeling the grafted polymer will also give information unique to SANS.

Atomistic Simulations with Carbon Nanotubes - Classical, Quantum, and Transport Modeling

Theoretical modeling of carbon nanotubes continues to provide useful insight and guidance to many experimental efforts toward technological applications. Molecular modeling tools have been used to study important structural, electronic, elastic, transport, and growth properties of nanotubes. We report results from three recent simulations: (i) effect of adsorbates on field emission from a nanotube tip; (ii) effect of mechanical deformation and chirality of nanotubes on electronic transport; and (iii) coating and solubilizing nanotubes by a polymer. The reported simulations are based on first principles density functional theory (DFT), classical molecular mechanics, and tight-binding transport based on the Green's function formalism.

Corrosion behaviour of stressed magnesium alloys

Potentiodynamic polarisation and impedance measurements are used to examine the corrosion aspects of some Mg-based alloys, which were previously stressed in order to established the effect of mechanical deformation on surface electrochemical reactions. A first approach was made for the unstressed alloys. The electrochemical tests were carried out in a sodium borate buffer solution.

Modeling deformation effects on Tc in epitaxial films of La 1.9Sr 0.1CuO 4

A model is presented for the effect of mechanical deformation on the critical temperature in epitaxial films of strontium-doped lanthanum cuprate. The model, which accounts for the interior geometry and deformation of the crystalline cell, yields predictions that agree remarkably well with the experimental findings of Locquet et al. [Proc. SPIE 3481 (1998)].

Effect of mechanical deformation of neutrophils on their CD18/ICAM-1-dependent adhesion.

Mechanical deformation of polymorphonuclear leukocytes (PMN) changes their expression of the surface adhesion molecule CD11b/CD18. We tested the hypothesis that mechanical deformation of PMN enhances their adhesiveness. Purified human PMN were deformed through either 5- or 3-microm polycarbonate membrane filters and allowed to adhere to 96-well plates coated with human recombinant intercellular adhesion molecule-1 (ICAM-1). Flow cytometric studies showed that deformation of PMN increased CD11b/CD18 expression (P < 0.01). PMN adhesion to ICAM-1-coated plates was dependent on the magnitude of cell deformation (5 microm, 63.8 +/- 8.1%, P < 0.04; 3 microm, 232.4 +/- 20.9%, P < 0.01). Priming of PMN (0.5 nM N-formyl-methionyl-leucyl-phenylalanine) before deformation (5 microm) increased PMN adhesion (63.8 +/- 8.1 vs. 105.3 +/- 16.4%; P < 0.04). Stimulation (5% zymosan-activated plasma) of PMN after deformation resulted in increased adhesion, and the degree of increase was dependent on the magnitude of PMN deformation (stimulation, 50.6 +/- 4%; 5-microm filtration and stimulation, 62.9 +/- 6.6%; 3-microm filtration and stimulation, 249.9 +/- 24.2%; P < 0.01). This study shows that mechanical deformation of PMN causes an increase in PMN adhesiveness to ICAM-1 that was enhanced by both priming of PMN before deformation and stimulation after cell deformation.

The effect of mechanical deformation on the phase transformation of BSCCO superconductors

Mechanical deformation has been widely used to produce textured microstructures to improve the critical current density of Bi2223 superconducting tapes. However, the effect of mechanical deformation on the phase transformation of the BSCCO system has not been well understood. The present research studies the relations between mechanical deformation and the phase transformation kinetics. The results showed that the Bi2223 phase abundance firstly decreased when the mechanical deformation was increased from 20% to 60%, and then increased as the deformation was increased above 60%. The 60% thickness reduction, therefore, resulted in the lowest Bi2223 phase abundance. The effects of mechanical deformation on the distribution of the Bi2223 phase across the thickness of the tape and the grain size of Bi2223 and Bi2212 phases were also studied. The experimental results have been explained by considering the different dominant energies associated with the different mechanical deformation regimes.

Characteristics of micro-texture and meso-texture in(Bi, Pb)2Sr2Ca2Cu3O10 superconducting tapes

Grain boundary misorientation is known to limit the critical currentdensity of bulk high temperature superconductors. However, the effect ofmechanical deformation on the texture evolution during powder-in-tube (PIT)processing remains unclear, especially on the microstructural level. In thepresent work, the micro- and meso-texture characteristics of PIT-processed(Bi, Pb)2Sr2Ca2Cu3O10 (Bi2223) superconductor tapes wereinvestigated. The results for micro-texture show that a/b-axes texture doesexist in PIT-processed tapes. From the meso-texture studies, it was found thata majority of the grain boundaries were formed by grains with a non-parallelc-axis. These grain boundaries generally have low mismatch angles of up to~10°. High-angle misorientation boundaries ranging up to45° are generally c-axis twist boundaries. Furthermore, about 40% ofthe grain boundaries could be coupled strongly.

Apparatus for Studying the Effect of Mechanical Deformation on the Permeation of Organics through Polymeric Films

A new experimental apparatus for studying the effect of mechanical deformation on the permeation of organic compounds through polymeric membranes is described. The apparatus consists of a custom-built biaxial membrane stretching device and an ASTM F739 permeation cell. Infrared spectroscopy was used as the analytical technique to measure, in real time, the downstream concentration of organic compounds that passed through the membrane. The equipment was used to monitor the permeation of single organic liquids and organic mixtures through uniaxially and biaxially elongated membranes composed of polyisoprene rubber and carbon black. The steady-state flux of acetone through a 40% uniaxially deformed membrane increased by 100%, as compared to that for a nonelongated film, whereas the acetone flux decreased by 25% when the membrane was deformed biaxially 40x40%. Variations in membrane thickness with stretching were small and could not account for the observed change in acetone flux with uniaxial elongation. For an equivolume feed mixture of acetone, benzene, and hexane, the steady-state permeation of all three compounds increased when the membrane was elongated 40x40%, as compared to the nonstretched case. Some deterioration of the membrane occurred during permeation of pure benzene with biaxial stretching (40x40%), as evidenced by a step-jump increase in the benzene flux. No deterioration was observed with nonelongated and uniaxially stretched films.

Micro-indentation and scanning probe microscopy to assess multilayer magnetic film damage

We have combined several techniques to evaluate the effect of mechanical deformation on the topography and magnetics of an underlying thin magnetic film. Micro-indentation techniques are used to introduce tailored deformations to magnetic recording disks. Atomic force microscopy (AFM) and magnetic force microscopy (MFM) then map out the topography of the indentations and the effect on the underlying magnetic film. Indentation morphology includes pyramidal and conical indents, linear scratches, and reciprocating wear tracks. The extent of topographical damage assessed by AFM correlates with the carefully controlled normal and tangential forces of the micro-indenter. Sub-surface `damage’ is assessed by MFM, monitoring for loss of resolution in pre-written magnetic data tracks. Mechanical tests are conducted at very low speeds and loading rates; hence, frictional heating or other thermo-mechanical factors that might cause ambiguities in data interpretation can be safely ruled out. By using the combination of micro-mechanical testing, Raman spectroscopy, and AFM/MFM techniques, we have found that mechanically introduced bit contrast degradation is attributed to physical modification of the magnetic coating and protective overlayer. The indentation and scratch tests both confirm that static pressure alone is not sufficient to cause the observed magnetic degradation; other mechanical factors must be invoked, including alteration of the geometry of the magnetic coating. Micro wear is capable of causing magnetic damage at much lower pressures than indentations or scratches. From wear track data, the degree of disk surface damage is correlated with the degree of magnetic bit contrast degradation. From wear track data on DC-erased samples it is concluded that mechanical deformation can induce magnetic contrast via concerted reorientation of grain c-axis and, hence, reorientation of magnetic moments.

Reversible electromechanical characteristics of carbon nanotubes under local-probe manipulation

The effects of mechanical deformation on the electrical properties of carbon nanotubes are of interest given the practical potential of nanotubes in electromechanical devices, and they have been studied using both theoretical and experimental approaches. One recent experiment used the tip of an atomic force microscope (AFM) to manipulate multi-walled nanotubes, revealing that changes in the sample resistance were small unless the nanotubes fractured or the metal-tube contacts were perturbed. But it remains unclear how mechanical deformation affects the intrinsic electrical properties of nanotubes. Here we report an experimental and theoretical elucidation of the electromechanical characteristics of individual single-walled carbon nanotubes (SWNTs) under local-probe manipulation. We use AFM tips to deflect suspended SWNTs reversibly, without changing the contact resistance; in situ electrical measurements reveal that the conductance of an SWNT sample can be reduced by two orders of magnitude when deformed by an AFM tip. Our tight-binding simulations indicate that this effect is owing to the formation of local sp3 bonds caused by the mechanical pushing action of the tip.