Changes In Material Parameters Research Articles

Change of material parameters of lead zirconate titanate rings after applying non-uniform mechanical stress

Lead zirconate titanate rings were subjected to different mechanical stress applied by bolt clamping. The piezoelectric and elastic coefficients, the relative permittivity and the electromechanical coupling factor of the compressed rings were evaluated from the impedance and phase spectra using a commercial package “Piezoelectric Resonance Analysis Program” (PRAP). The results show that the piezoelectric coefficient e 33, elastic coefficient c 33 D and electromechanical coupling factor k t decreased, while the relative permittivity ε 33 S/ ε 0 increased with the increase in mechanical stress. The changes of the material parameters of the compressed rings are understood from the movements of domain walls upon the application of different torques.

Nonlinear time-dependent response of isotactic polypropylene

Tensile creep tests, tensile relaxation tests and a tensile test with a constant strain rate are performed on injection-molded isotactic polypropylene at room temperature. A constitutive model is derived for the time-dependent behavior of semicrystalline polymers. A polymer is treated as an equivalent network of chains bridged by permanent junctions. The network is modeled as an ensemble of passive mesoregions (with affine junctions) and active mesodomains (where junctions slide with respect to their reference positions with various rates). The distribution of activation energies for sliding of junctions in active mesoregions is described by a random energy model. Adjustable parameters in the stress–strain relations are found by fitting the experimental data. It is demonstrated that the concentration of active mesodomains monotonically grows with strain, whereas the average activation energy for sliding of junctions and the standard deviation of energies suffer substantial down jumps in the vicinity of the yield point. With reference to the concept of dual population of lamellae, these changes in material parameters are attributed to transition from breakage of subsidiary (thin) lamellae in the subyield region to fragmentation of dominant (thick) lamellae in the postyield region of deformations.

Strain Measurement in Coronary Arteries Using Intravascular Ultrasound and Deformable Images

Atherosclerotic plaque rupture is responsible for the majority of myocardial infarctions and acute coronary syndromes. Rupture is initiated by mechanical failure of the plaque cap, and thus study of the deformation of the plaque in the artery can elucidate the events that lead to myocardial infarction. Intravascular ultrasound (IVUS) provides high resolution in vitro and in vivo cross-sectional images of blood vessels. To extract the deformation field from sequences of IVUS images, a registration process must be performed to correlate material points between image pairs. The objective of this study was to determine the efficacy of an image registration technique termed Warping to determine strains in plaques and coronary arteries from paired IVUS images representing two different states of deformation. The Warping technique uses pointwise differences in pixel intensities between image pairs to generate a distributed body force that acts to deform a finite element model. The strain distribution estimated by image-based Warping showed excellent agreement with a known forward finite element solution, representing the gold standard, from which the displaced image was created. The Warping technique had a low sensitivity to changes in material parameters or material model and had a low dependency on the noise present in the images. The Warping analysis was also able to produce accurate strain distributions when the constitutive model used for the Warping analysis and the forward analysis was different. The results of this study demonstrate that Warping in conjunction with in vivo IVUS imaging will determine the change in the strain distribution resulting from physiological loading and may be useful as a diagnostic tool for predicting the likelihood of plaque rupture through the determination of the relative stiffness of the plaque constituents.

General equivalent circuit of batteries and fuel cells

A general electrical circuit is described whose properties are analogous to those of fuel cells and batteries. It is shown how this equivalent circuit model can show the influence of changes in material parameters upon the output of such physical systems. As an example, the significance of the transference numbers of minority electronic and ionic charge carriers in the electrolyte on the output voltage of fuel cells and batteries is readily seen.

Time-Frequency Resolved Coherent Raman Scattering From Molecular Liquids and Their Mixtures With Quasi-Cw Noisy Light: I(2) CRS Spectrograms

It is demonstrated how time-frequency resolved coherent Raman scattering (CRS) signals generated by broadband, non-transform limited, quasi-cw (noisy) light can be sensitive probes of molecular vibrational dynamics. The coherent Raman scattering signals from molecular liquids and their mixtures with noisy light are dispersed onto a CCD array and probed interferometrically to produce time-frequency domain spectrograms. These spectrograms offer an extensive oversampling of the data resulting in improved precision of measured parameters over previous noisy light methods. This technique has been very useful in measuring small changes in material parameters, such as Raman frequency shifts and linewidth changes, in dilution series with Raman inactive diluents. Very recently theory and experiment have extended to include mixtures with multiple Raman resonances. Several examples of experiments are presented and discussed.

Critical factors affecting the high-temperature corrosion performance of iron aluminides

Iron aluminides are known to exhibit good-to-excellent corrosion resistance in a number of high-temperature environments. Under most conditions, this resistance derives from the establishment and maintenance of a sound and adherent alumina layer. Consequently the performance of iron aluminides under different aggressive high-temperature can be related to fundamental factors that affect the development, adhesion, and durability (lifetime) of protective alumina. Overall corrosion resistance depends not only on thermodynamic stability of the reaction product in a particular environment and its growth kinetics, but also on scale integrity and morphology, the chemical and physical nature of the oxide–metal interface, alloy strength, and the specific composition of the iron aluminide. Despite the multiplicity of factors, a relatively simple lifetime prediction model based on aluminum consumption can be used to evaluate the influences of changes in material parameters and to determine approaches to improving high-temperature corrosion resistance of iron aluminides.

Investigations on ferroelectric liquid crystalline systems with the laser intensity modulation method

Spatially resolved polarization and charge distributions have been investigated in sandwich cells of two ferroelectric liquid crystal side-chain polymers and a low molecular weight ferroelectric mixture. For measurements without external field, contributions to the distribution at the surface of the liquid crystal layer have been found for all three materials. These are attributed to nonvanishing polarization due to surface interaction of the molecules. For both polymeric materials there is a strong dependence of the shape of the measured pyrospectra on the sample temperature. This is attributed to changes in material parameters. In contrast to this, for the low molecular weight substance only minor changes are visible. For an applied external electric field, additional contributions to the resulting distribution caused by charge layers and by polarization due to helix unwinding can be observed. Charge layers are located near the surface of the liquid crystal layer. Helix unwinding can be observed for the low molecular weight material at room temperature. One of the polymers which is in the glassy state at room temperature shows corresponding effects above its glass transition point. © 1998 John Wiley & Sons, Ltd.

Anomalies of ferroelectric domain wall motion near the transition point

Optical measurements of the individual ferroelectric/ferroelastic domain wall oscillations in the ac electric field were carried out up to the transition temperature. The amplitude of the wall vibrations fell abruptly to zero so that the wall was at rest during the phase transition. The change of oscillation characteristics with temperature is shown to be dependent on the history of motion, in part on the initial amplitude and the presence of the shell of mobile defects or charge carriers. Change of material parameters, influence of screening or defects shell, and critical damping are discussed as possible mechanisms of the effect. The last assumption is shown to be in a good agreement with the experimental data. The measurements of the amplitude of domain wall vibrations may be used as a simple method for investigations on critical phenomena in ferroelectrics.

In situ computerized optical reflectivity measurement system for ion implantation

A computerized in situ optical reflectivity measurement system for the quantitative determination of material parameter changes of a substrate during the process of ion implantation is presented. These changes are related to the extent and nature of the induced crystal disorder in the substrate. The system consists of an optical reflectometer, with data acquisition and signal processing capabilities. For each sample a case history of the implant is obtained in the form of a continuous graph of reflectivity vs. a desired implantation parameter (e.g. dose). Examples regarding the implantation of /sup 31/P/sup +/, /sup 40/Ar/sup +/, and /sup 14/N/sup +/ are presented. Additional suggestions for further system development and applications are made. Among the advantages of in situ measurements are the time-effort-expense. savings, a higher yield of experimental data per sample, higher accuracy, repeatability, and various possibilities of process control.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Modeling of discontinuities in general coaxial waveguide structures by the FDTD-method

The finite-difference time-domain (FDTD) method is used to model generalized coaxial waveguide structures with discontinuities. The cross section of the waveguide consists of a closed outer conductor and one or two inner conductors of arbitrary shape. The cross section can have any number of dielectric materials with losses. The singular field-behavior near sharp edges is explicitly included in the finite-difference scheme. Any kind of discontinuity can be handled: changes in cross-section as well as changes of material parameters. From the time-domain data, frequency-domain data (S-parameters) are obtained using Fourier-transform techniques.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

プラズマ回転電極法による均一球形粉末製造の検討とその金属間化合物への応用

Atomization mechanism and production of atomized high quality powder by Plasma Rotating Electrode Process (PREP) were discussed. The atomization mechanism changed from direct drop formation (DDF) to film disintegration (FD), through ligament disintegration (LD) depending on either the changes in material parameters or those in the operation parameters. DDF mechanism yielded the highest quality powder particles consisting of exceedingly spherical shape, uniform size and clean without contamination. Therfore, this powder seemed to be suitable for compaction by Wing or near-net-shape forming. The results of the study were applied for producing PREPed powders of some intermetallics such as Ti-aluminides and TiNi. The compacts of those powders showed improved mechanical properties compared with the conventionally processed materials.

Radiation effects in high temperature superconducting films and devices for the NRL high temperature superconductivity space experiment

The effects of proton irradiation on the performance of films and microwave devices made from the high temperature superconductors YBa/sub 2/Cu/sub 3/O/sub 7- delta / and Tl/sub 2/Ca/sub 2/BaCu/sub 2/O/sub 8/ have been measured and can be explained in terms of radiation-induced changes in material parameters such as surface impedance, critical current and transition temperature. Changes in material parameters can in turn be linked to atomic displacement effects.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Free‐field response from inclined body waves in a viscoelastic random medium

AbstractThis paper deals with the free‐field response of the in‐plane motion resulting from a combination of inclined incident body waves. The amplification of waves in a viscoelastic layer with stochastic changes in the elastic properties and density is investigated. The method used is that of Karal and Keller and is based on the idea of the fundamental matrix. The third order correlations are neglected. The resulting integro‐differential equations for the average displacements are solved by the Laplace transform. Generally, analysis indicates that the stochastic changes in the shear modulus and density enhance the damping in a significant manner. However, increases in the waves' amplification can arise in the case of a small dimensionless frequency and uncorrelated stochastic changes of material parameters.

Total dose and transient radiation effects on GaAs MMICs

To elucidate the effects of radiation on GaAs monolithic microwave integrated circuits (MMICs), radiation-induced changes in DC parameters of test FETs and in the measured microwave performance of MMICs were compared. Changes in material parameters determined from the DC results were used to model the observed microwave performance degradation. In addition, the effect of accumulated radiation damage in MMICs was studied in terms of the amplifier response to transient radiation pulses. The effect of 1-MeV electron irradiation on microwave response and transient radiation pulse response was measured in 0.5- to 12.5-GHz distributed amplifiers (ion-implanted) and in 28-GHz power amplifiers (with epitaxially grown active layers).< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Hysteretic Endochronic Theory for Sand

A new form of endochronic constitutive model is presented to describe the behavior of dry or drained sand, and its parameters are determined by extensive comparisons with published test data. Jump‐kinematic hardening is used to guarantee that the hysteresis loops always close, yield positive energy dissipation, and give an increase in tangent modulus when unloading changes to reloading. Criteria for virgin loading, unloading and reloading are formulated in terms of deviatoric work, and changes of material parameters at loading‐unloading‐reloading transition points are determined. Two endochronic units coupled in parallel are used to describe the measured response over a broad range of strain amplitude. The inelastic volume change is characterized so as to include both densification and dilatancy. Certain material properties are determined as functions of the void ratio. Calculations show that the lateral stress in a simple shear test quickly becomes almost equal to the vertical stress. A three‐dimensional finite element analysis of the simple shear test with endochronic theory reveals significant stress nonuniformity; but this is found to have little effect on the resulting hysteresis loops.

A new low-voltage electrically-addressed bistable nematic liquid-crystal boundary-layer display

A method of electrical switching between the bistable states of a recently reported display is described [p. 1007, [5]]. The topologically-equivalent bistable states have boundary-inversion (BI) layers adjacent to one or the other of the cell surfaces. The display allows low-voltage operation, is capable of good contrast, and is relatively insensitive to changes in material parameters, boundary conditions, and temperature. In the described method of switching, the state is selected by the height of an ac switching voltage in a suitably fabricated asymmetrical cell. A low switching voltage, by a process that is uniform over the pel area, quickly produces the state with the BI layer at the surface favored by the cell's asymmetry. A somewhat higher voltage produces the other state by a domain wall slowly shrinking from the pel perimeter. The write time (uniform process) can be as short as 50 ms, but the erase time (domain wall motion) is more than a second.

The influence of material parameters on nonuniform plastic flow in simple tension

The development of nonuniform plastic flow in a strain hardening and strain rate sensitive metal is examined under simple tension. The analytical model assumes that the localized deformation develops from an initial geometric nonuniformity in the test specimen and the axial stress is uniform in the cross section. All the material constants and parameters in the constitutive equation are derived from simple tension and load relaxation tests for a variety of metals. It is shown that the early stage of localized deformation as indicated by the computed profiles of the gage section is in good agreement with the experimental data. The results of the computed and experimental stress-strain curves are also in agreement, except at the final stage of necking where the hydrostatic stress is known to play an important role. Implications of the computed limiting strain and gage section strain with changes in material parameters are discussed by comparing the results with measured strains to fracture.

Radiation Effects in Gaas Junction Field-Effect Transistors

GaAs field-effect transistors for linear and digital circuits are finding applications in systems that have to function in a nuclear environment. This paper reviews and analyzes the radiation damage mechanisms in GaAs material and applies the material parameter changes to predict changes of electrical parameters of junction field-effect transistors due to exposure to fast neutrons and total dose ionizing radiation. The transient response to pulsed ionizing radiation is analyzed and experimental results are correlated with theoretical predictions. Annealing characteristics of radiation-generated defects are described. The prospects for hardening GaAs fieldeffect transistor integrated circuits against the effects of nuclear radiation are assessed.

Interpretation of elastic-wave scattering theory for analysis and design of flaw-characterization experiments: The long-wavelength limit

Recently, the results of a general theory of the scattering of elastic waves from a flaw embedded in an isotropic medium were shown in the far-field limit to be compactly represented by a single vector, the f vector. Studying the f vector is thus a way to investigate systematically the dependence of the scattering on the polarization of the incident mode, scattering angle, changes in material parameters, and shape. In the long-wavelength limit the f vector is exactly determinable and exhibits significant features of the flaw. We discuss long-wavelength scattering results for volume flaws and idealized cracks and compare some of the results with those of the Born approximation, which has already been calibrated by comparison to exact calculations and experiment.

A Comparison of Fast Neutron Irradiation Effects in Photoconductive and Photovoltaic InSb Infrared Detectors

The relative neutron irradiation hardness of photoconductive and photovoltaic InSb infrared detectors is examined for various operating modes and conditions. It is found that photoconductors are much less vulnerable to fast neutrons at 78K than are photovoltaic detectors. The damage mechanisms for photovoltaic detectors are increased leakage currents coupled with a decrease of minority carrier lifetime in the bulk region with a damage constant of 1.5 × 10-14 ?m-2 n-1 cm2, while a carrier removal rate of 1.1 cm-1 is established for 14 MeV neutron-irradiated p-type InSb with an initial carrier concentration of ~3 × 1014 cm-3. It is shown that these changes in material parameters can be used to predict fast neutron damage under all realistic operating conditions. The effects of neutron irradiations on signal, noise, current-voltage characteristics and spectral response are discussed in detail.