Effect Of Uniaxial Deformation Research Articles

Effect of uniaxial deformation along the trigonal axis on the band structure of bulk bismuth

Effect of uniaxial deformation along the trigonal axis on the band structure of bulk bismuth

EFFECT OF DEFORMATION ON MIGRATION RATE OF GRAIN BOUNDARIES IN NICKEL

Effect of deformation along various directions against migrating boundary on migration rate of edge boundaries with <100> and <111> misorientation axes in nickel was studied by means of molecular dynamics method. Grain boundaries were created in U-shaped model. Force of boundary surface tension, arising from the boundary intension to minimize its energy, was the reason of directed movement of the boundary toward its area decrease. The force provoking migration and migration rate of the boundary remained constant throughout the entire movement of the boundary, gradually decreasing towards the end of computer experiment, which made it possible to measure migration rate quite simply. Effect of uniaxial deformation along the X, Y, Z axes on migration rate of the boundaries was considered. Uniaxial deformation in the model was set at beginning of the computer experiment by changing corresponding interatomic distances along one of the axes. Interactions of nickel atoms with each other were described with the aid of Cleri Rosato many-particle potential constructed in the framework of tight binding model. For the boundaries considered, dependences of migration rate on misorientation angle at temperature of 1700 K were obtained. It is shown that the high-angle <111> and <100> edge boundaries migrate approximately at the same rate, while mobility of low-angle boundaries differs significantly: low-angle <111> boundaries migrate about twice as fast as the <100> boundaries. It was found that in almost all cases, both at elastic compression and tension deformation, migration rate of considered boundaries was slowed down. An exception was the case of deformation along the <111> edge boundary axis. When compressing along the edge axis, <111> boundary migrated faster, while on the contrary, it was slower at tension. The obtained results testify to the fact that migration of edge boundaries is not due to diffusion processes, such as climbing of dislocations, single migrations of atoms, but, apparently, by collective atomic permutations: shifts, slides and splittings of grain boundary dislocations.

Effect of uniaxial deformation on the current–voltage characteristic of a p-Ge/n-GaAs heterostructure

The effect of uniaxial deformation under a stress of up to 6 kg/cm2 on the current–voltage characteristics of a p-Ge/n-GaAs heterostructure is studied at 300 and 77 K. It is found that both the forward and reverse currents increase with increasing pressure, with the change in the forward current exceeding that in the reverse current by an order of magnitude. Deformation is also examined in relation to different crystallographic directions. It is found that the effect is at a maximum if the compression direction is parallel to . This result can be used in the development of uniaxial-strain sensors.

Effect of Uniaxial Deformation on Structure and Transport in Hydrated Nafion 117: Molecular Dynamics Simulation Study

Abstract The deformation of hydrated Nafion 117 was implemented using full-atomistic molecular dynamics simulation method to elucidate how the mechanical deformation affects the structure and transport of hydrated Nafion membrane. First, Nafion 117 membrane was equilibrated with 20 wt. % water content through an annealing procedure. The simulated characteristic correlation length and the diffusion coefficient of water and hydronium ions were analyzed for comparison with those observed in experiments. Then, the equilibrated Nafion membrane was deformed uniaxially up to 300 % of strain with a constant strain rate. The change in nanophase-segregation of hydrated Nafion during the deformation process was characterized using a directional structure factor as well as the pair correlation function in order to achieve fundamental understanding of the relationship of such structural change as a function of strain with the proton transport. It was found from the pair correlation analysis that the sulfonate distribution and sulfonate-hydronium correlation became stronger through the deformation while the hydronium ion solvation and the internal structure of water phase were not dependent on the deformation. From the directional structure factor profile, it was found that the long range correlation was developed in the perpendicular direction to the extension. The diffusions of water and hydronium ions were enhanced by 30 and 2 %, respectively, after the deformation. From this study, we suggested that it is desirable to investigate the proton transport using simulation methods covering larger dimensions with a long time scale.

Effect of uniaxial deformation on the structure and hysteresis magnetic characteristics of a hard magnetic alloy Fe-22% Cr-15% Co

The structure and magnetic hysteresis characteristics of anisotropic samples of a hard magnetic alloy Fe-22% Cr-15% Co subjected to uniaxial plastic deformation at a temperature up to 400°C are investigated. It is established that the maximum energy product of the anisotropic samples decreases substantially after deformation at a retained coercive force and remanence, while the maximum energy product of isotropic samples increases somewhat after deformation. The variation of the magnetic properties is related to the structure evolution during deformation.

Effect of uniaxial deformation on the number of pairs of inversely populated electronic states

Simple electronic spectra are considered in the tight-binding approximation for the case of uniform uniaxial deformation. It is shown that there is a range of deformations (considerably exceeding a threshold one) in which conditions for the generation of phonons by nonequilibrium electrons are satisfied. Moreover, in this range an increase in the deformation is accompanied by an increase in the number of pairs of potentially active electronic states. The effect is pronounced more strongly in the case of tensile deformation. The results obtained are important for the development of the theory of reconstructive martensitic transformations.

Atomic force microscopy observations of the structural development during the uniaxial stretching of crosslinked low‐density polyethylene in partial and fully molten states

AbstractThe effect of uniaxial deformation in partially and fully molten states on the morphology of crosslinked low‐density polyethylene has been investigated. At low temperatures, the morphology is predominantly fibrillar, with little kebabs appearing on the fibril surfaces. As the deformation temperature is increased into the melting range, the shish density decreases, and overgrowths of kebabs on the fibrils concurrently increase in length. This gives rise to added twisting of the kebabs reflected in the orientation factor analysis. This shish/twisted lamellar kebab texture is observed only in a partially molten state. Studies in a substantially molten state indicate the absence of shish, althugh short lamellae are observed that are oriented in the transverse direction. This morphology indicates a high chain orientation factor as a result of short lamellae that exhibit small twisting similar to Matsumura's rod model. The absence of shishes in the final films stretched isothermally in a substantially molten stage agrees with Schultz's model, in which imperfectly formed shishes dissolve if they are not stabilized by rapid cooling, as is the case in these studies. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2228–2237, 2004

Effect of uniaxial strain on the protective properties of coil-coatings

The effect of uniaxial deformation on coil-coated galvanised steel was investigated. Samples with several degrees of uniaxial elongation were exposed to a corrosive solution and the loss of protective properties was monitored by electrochemical impedance spectroscopy (EIS). Protection rapidly decreased with the degree of elongation. After 16% the coating degradation introduced by elongation was so high that EIS was not able to distinguish different strained samples. The loss of protection was interpreted in terms of the morphological changes experienced by the coated system as a consequence of strain, supported by scanning electron microscopy (SEM) observations.

Influence of deformation on irreversible and reversible crystallization of poly(ethylene‐co‐1‐octene)

AbstractThe effect of uniaxial deformation and subsequent relaxation at ambient temperature on irreversible and reversible crystallization of homogeneous poly(ethylene‐co‐1‐octene) with 38 mol % 1‐octene melt‐crystallized at 10 K min was explored by calorimetry, X‐ray scattering, and Fourier transform infrared spectroscopy. At 298 K, the enthalpy‐based crystallinity of annealed specimens increased irreversibly by stress‐induced crystallization from initially 15% to a maximum of, at least, 19% when a permanent set of more than 200% was attained. The crystallinity increased by formation of crystals of pseudohexagonal structure at the expense of the amorphous polymer, and as a result of destruction of orthorhombic crystals. The stress‐induced increase of crystallinity was accompanied by an increase in the apparent specific heat capacity from 2.44 to about 2.59 J g−1 K−1, which corresponds to an increase of the total reversibility of crystallization from, at least, 0.10 to 0.17% K−1. The specific reversibility calculated for 100% crystallinity increased from 0.67 to 0.89% K−1 and points to a changed local equilibrium at the interface between the crystal and amorphous phases. The deformation resulted in typical changes of the phase structure and crystal morphology that involve orientation and destruction of crystals as well as the formation of fibrils. The effect of the decrease of the entropy of the strained melt on the reversibility of crystallization and melting is discussed. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1223–1235, 2002

The effect of uniaxial deformation on swollen gels

The effect of uniaxial deformation on swollen gels is investigated. The elastic contribution is obtained by a extension of the modified Flory model proposed previously. Following Bastide, it is assumed that the deformation occurs by a process of topological rearrangements of the cross-link junctions. Consequently, the contracted junction affine model is used to describe the relationship between the macroscopic deformation and the resulting chain deformation. Using this simple approach, we examine the effect of deformation on the relative degree of swelling ( φ g /φ gm ) and the packing factor.

Effect of mechanical processing on giant magnetoresistance in melt-spun Co–Cu ribbons

We have investigated the effect of uniaxial deformation on the giant magnetoresistance (GMR) effect in melt-spun Co–Cu ribbons. Postprecipitation deformation does not affect the Co particles, but the mechanical processing increases the structural disorder and the resistivity; thus the GMR effect is degraded. Deforming the metastable alloy prior to precipitation of the Co particles possibly affects the particle nucleation process. As a result, the low-field sensitivity of the GMR effect increases slightly.

Effect of uniaxial deformation on the optical scattering losses of a semicrystalline fluorocopolymer

Both small- and wide-angle light scattering as well as transmission measurements have been used to investigate the optical scattering losses of a vinylidene difluoride-tetrafluoroethylene-hexafluoropropylene copolymer crystallized from the melt. The main origin of the scattering loss is the wide-angle light scattering from the spherulitic superstructure. Uniaxial deformation transforms this structure into a fiber morphology. The attenuation of fibers has been measured for light propagating both parallel and perpendicular to the orientation axis. For both directions, the attenuation decreases with increasing draw ratio. Annealing of the fibers while keeping their ends fixed is an effective method to reduce the attenuation further, to a low value as close to that of the melt.

Impurity States and Optical Transitions in Uniaxially Deformed Narrow‐Gap Semiconductors

AbstractThe effect of uniaxial deformation along cubic axis on the states of point defects in narrow‐gap semiconductors is studied. The energy dependence of the splitting of deep h‐states into two doubly degenerate h1 and h2 states on the deformation value and the semiconductor characteristics is calculated. Changes of optical transitions from deep 1‐c and h‐centres with deformation are also examined. It is shown, that the absorption coefficient in this case is essentially anisotropic and its spectral dependences essentially differ from those in the case without deformation.

The possibility of creating β-rhombohedral boron-based semiconductor devices

This paper reports studies of the electroresistivity, I- V characteristics and time parameters in switching effects of β boron. The effect of uniaxial deformation on some parameters of the material under study is also considered. The piezoresistance and tensor-sensitivity coefficient of β boron was determined over a wide temperature range, β boron crystals are proposed for the development of a number of semiconductor devices.

Finite deformation and tensile strength of polystyrene and polyethylene solids

AbstractFor samples of amorphous polystyrene and partial crystalline polyethylene, the fracture strengths for different degrees of uniaxial flow deformation are determined and are found to agree fairly well with theoretical predictions. For hard polymers, the effect of uniaxial deformation upon the tensile breaking stress of a simplified model solid is discussed. The fracture strength in any direction of this model material may be determined by obtaining the expectation of the strength components of a system of perfectly oriented model elements in that direction.