Variation Of Material Parameters Research Articles

Optical Conductivity Measurement of a Dimer Mott-Insulator to Charge-Order Phase Transition in a Two-Dimensional Quarter-Filled Organic Salt Compound

We report a novel insulator-insulator transition arising from the internal charge degrees of freedom in the two-dimensional quarter-filled organic salt β-(meso-DMBEDT-TTF)2PF6. The optical conductivity spectra above Tc=70 K display a prominent feature of the dimer Mott insulator, characterized by a substantial growth of a dimer peak near 0.6 eV with decreasing temperature. The dimer peak growth is rapidly quenched as soon as a peak of the charge order appears below Tc, indicating a competition between the two insulating phases. Our infrared imaging spectroscopy has further revealed a spatially competitive electronic phase far below Tc, suggesting a nature of quantum phase transition driven by material-parameter variations.

Influence of ambient temperature variations on the performance of Lyot depolarizers

The influence of temperature on the efficiency of Lyot depolarizers is analysed. It is a commonly used idealization that if the birefringent sections forming the depolarizer are made long enough with respect to the coherence time of the lightwave then strictly complete depolarization is always assured. This can lead to a false conclusion that in a real-world system the residual degree of polarization (DoP) will reach a certain value, slightly higher than zero, and remain independent of the initial polarization state (SoP) and insensitive for small variations of material parameters. We point out that Lyot depolarizers are always inhomogeneous in general and, thus, a precise estimation of the maximum possible DoP of an emerging lighwave is not trivial. Using a system made of two sections of lithium niobate we examine and explain how environmental temperature variations within the range of 1 ° C can significantly affect the depolarization efficiency. The numerical predictions of the effect have been verified qualitatively in experiments.

Optimization of structures under material parameter uncertainty using evidence theory

An evidence-based approach is developed for optimization of structural components under material parameter uncertainty. The approach is applied to evidence-based design optimization (EBDO) of externally stiffened circular tubes under axial impact load using an isotropic–elastic–plastic plasticity model to simulate dynamic material behaviour. Uncertainty modelling considers the changes in material parameters that are caused by variability in material properties as well as incertitude and errors in experimental data and procedure to determine the material parameters. Spatial variation of material parameters across the structural component is modelled using a field joint belief structure and propagated for the calculation of evidence-based objective function and design constraints. Surrogate models are used in both uncertainty propagation and solution of the optimization problem. The methodology and the solution to the EBDO example problem are presented and discussed.

Tolerance Prediction for Forming Force of Upsetting-Extruding Process by Using Points of Monomial Cubature Rules

An efficient method for estimating the range of forming force for an upsetting-extruding process was proposed, which may be useful to choose appropriate forming equipment. The accurate prediction of the forming force of an upsetting-extruding process is the key to form a work piece successfully. However, the forming force is variable in a certain range for the variation of material and process parameters. In general, the variation is dominated by some of the main effects and lower-order interactions due to the sparsity-of-effect principle. Therefore, the construction of polynomial chaos expansion with points of monomial cubature rules, which need fewer points than other kinds of integral, is particularly attractive in dealing with computational model for the forming simulation. An automobile threated plate is used to illustrate the validation of the method.

Modeling of Long Term Effects on Plasma Facing Components for a Fusion Power Reactor

In a fusion power reactor the Plasma Facing Components (PFC) will experience a thermal and neutron irradiation induced creep together with tensile properties degradation and swelling due to neutron irradiation. So the investigation of the long term creep effects on the materials used for the PFC’s in a fusion power plant are of vital importance for the design and safe operation of the device. On the other hand the creep behavior study for a given material requires long and expensive test campaigns, repeated on specimens at different levels of neutron irradiation, because of the material parameters variation due to the cumulated irradiation.In this work we want to investigate if the numerical mechanical simulations employment, according to a proper methodology, could reduce the number of needed creep tests, because this would be a valuable help in defining suitable materials and valid conceptual designs for PFC’s. For this reason a method based on the systematic variation of the parameters of the empirical law, e.g. the Norton-Bailey, is outlined. To exemplify it, the behavior of a simplified model is analyzed under thermal and mechanical cyclic loading in a time transient elasto-plastic simulation, including the creep behavior, varying the parameters in the empirical creep law for the material.

Security Reliability Analysis of Circulating Water Pump House Pit Excavation of Chen Jiagang Power Plant

The circulating water pump house pit excavation of Chen Jiagang power plant is characterized with complex geological and hydrological condition, high water level, and weakly permeable silt layer within the scope of pit excavation. Based on design and construction principles of safety, feasibility, rationality and economy, different foundation pit dewatering and support programs were analyzed and compared, a excavation method featured with well dewatering and steel pipe soil nails hanging net and stakes was elaborately designed, and establish a monitoring feedback system. And in the base of mathematical statistics, Taylor series method is used to analyze the reliability probability problems of excavation slope stability analysis. The successful implementation of the project indicated that the design and parameters of Chen Jiagang power plant circulating water pump house pit excavation is feasible, and Taylor series method combined with conventional safety factor is able to analyze the influence of material parameters variation on the excavation of the slopes safety.

A Seismic Reliability Assessment of Reinforced Concrete Integral Bridges Subject to Corrosion

This paper seeks to determine the effect deterioration has on the seismic vulnerability of a 3 span integral concrete bridge. Traditionally it has been common to neglect the effects of deterioration when assessing the seismic vulnerability of bridges. However, since a lot of the bridges currently being assessed for retrofit are approaching the end of their design life, deterioration is often significant. Furthermore, since deterioration affects the main force resisting components of a bridge, it is reasonable to assume that it might affect its performance during an earthquake. For this paper, chloride induced corrosion of the reinforcing steel in the columns and in the deck has been considered. Corrosion is represented by a loss of steel cross section and strength. A 3 dimensional non-linear finite element model is created using the finite element platform Opensees. A full probabilistic analysis is conducted to develop time-dependent fragility curves. These fragility curves give the probability of reaching or exceeding a defined damage limit state, for a given ground motion intensity measure taken as Peak Ground Acceleration (PGA). This analysis accounts for variation in ground motion, material and corrosion parameters when assessing its overall seismic performance as well as the performance of its most critical components. The results of the study show that all components experience an increase in fragility with age, but that the columns are the most sensitive component to aging and dominate the system fragility for this bridge type.

Fast Evaluation of Time–Harmonic Maxwell's Equations Using the Reduced Basis Method

The reduced basis method (RBM) generates low- order models for the solution of parametrized partial differential equations to allow for efficient evaluation in many-query and real-time contexts. We show the theoretical framework in which the RBM is applied to Maxwell's equations and present numerical results for model reduction in frequency domain. Using rigorous error estimators, the RBM achieves low-order models under variation of material parameters and geometry. The RBM reduces model order by a factor of 50 to 100 and reduces compute time by a factor of 200 and more for numerical experiments using standard circuit elements.

Continuous glass fiber reinforced wood plastic composite in extrusion process: Mechanical properties

This paper presents an experimental study on the material development where wood plastic composites (WPCs) were reinforced with continuous glass fibers (continuous hybrid WPC) at a low volume fraction. The continuous glass fiber reinforced WPC (CGFR-WPC) were produced in cylindrical profiles via an extrusion process. Experiments were carried out to investigate the effect of wood content, volume fraction of continuous glass fiber and the presence of coupling agent on the mechanical properties of the final products. Three point bending, tensile and impact tests were carried out on the extruded specimens. The results revealed an outstanding improvement in all the mechanical properties, where applying a low fraction of continuous reinforcement via incorporating six rovings of (continuous) fiber reinforcements into the WPCs, maximum increase in flexural, tensile and impact strength were observed to be 2.3, 5.9 and 20 times, respectively. Achieving these large increases in properties via conventional variations in processing and material parameters has not been reported. It is interesting to note that, when applying a larger number of reinforcements, presence of coupling agent in WPCs, exhibited a negative effect on the tensile properties.

Quantum-dot supercrystals for future nanophotonics

The study of supercrystals made of periodically arranged semiconductor quantum dots is essential for the advancement of emerging nanophotonics technologies. By combining the strong spatial confinement of elementary excitations inside quantum dots and exceptional design flexibility, quantum-dot supercrystals provide broad opportunities for engineering desired optical responses and developing superior light manipulation techniques on the nanoscale. Here we suggest tailoring the energy spectrum and wave functions of the supercrystals' collective excitations through the variation of different structural and material parameters. In particular, by calculating the excitonic spectra of quantum dots assembled in two-dimensional Bravais lattices we demonstrate a wide variety of spectrum transformation scenarios upon alterations in the quantum dot arrangement. This feature offers unprecedented control over the supercrystal's electromagnetic properties and enables the development of new nanophotonics materials and devices.

Revised metrology for enhanced accuracy in complex optical constant determination by THz-time-domain spectrometry

THz time-domain spectrometry (TDS) probes the complex polarization response of materials. Various analytical procedures are applied by many to extract the associated material optical constants. This has commonly been done by iteratively varying material parameters in order to achieve a match between experiment and a theoretical transfer function (TF). The poly root behavior of a TF is emphasized for measurements with reflections in the time domain. This study provides a comprehensive analysis of the influence of the initial guesses on the accuracy of extracted material parameters. In addition, various ways of representing multiple reflections inside the sample (a Fabry-Perot-like effect) are compared and their contribution to the uncertainty of material parameters is analyzed. Experimental evidence is provided where appropriate to support theoretical statements. Furthermore, this paper offers a basis for data comparison between different THz-TDS systems in transmission mode. Finally, a clear distinction is made between a commonly used basic analysis and an enhanced one, in terms of associated uncertainties in determination of the real and imaginary parts of the complex refractive index.

Thermomechanical Fatigue Characterization of Three Dimensional Compact Tension Specimens Made from Steel

When coupling with temperature is incorporated, the problem of fatigue is formulated within the general framework of thermomechanical fatigue. Considering the special case of steel structures, in addition to variations of material and fatigue parameters with temperature, fatigue damage depends on the phasing existing between the concomitant strain and temperature cycles. In this work, the extended finite element method is used to simulate crack growth under thermomechanical fatigue coupling. Assuming large cycle duration for which temperature variations can be considered to be uniform, this approach is applied in the context of linear elastic fracture mechanics for the particular case of the three dimensional Compact-Tension specimen. The objective is to attempt understanding more closely crack growth mechanism under thermomechanical loading. Characterization of fatigue was assessed as function of phasing and strain restraint.

Photo-controllable electro-optic response of liquid crystalline cells using photo-isomeric molecules

A photo-controllable liquid crystal (LC) material was evaluated using a nematic LC mixture with azobenzene. This study aimed to determine the mechanisms that result in variations of material parameters specifically caused by the morphological change of guest molecules. The transition from rod-shaped trans isomers to bent-shaped cis isomers weakened the intermolecular ordering interactions and the decreasing order parameter caused variations of material parameters. The shift of dielectric response cannot be solely explained by the weakened intermolecular interactions but is also significantly influenced by the properties of the guest cis isomer itself. The bend elastic constant was more affected than the splay elastic constant, which implies that the shift of the elastic properties is due to the morphological shape of the cis isomer as well as the decreased molecular ordering. Thus, three different mechanisms are involved in the variations of the material properties: (i) weakened intermolecular ordering interactions, (ii) direct contribution of cis isomers, and (iii) molecular morphological interactions of the cis isomer with the host LCs. It was also demonstrated that the optical properties of twisted nematic (TN) cells can be controlled, and that the stability of the bend state in the optically compensated birefringence (OCB) mode cell can be improved.

Bi doping modulating structure and phase-change properties of GeTe nanowires

Bi-doped GeTe nanowires were fabricated using chemical vapor deposition. Composition and microstructure characterizations indicated that Bi (∼3 at. %) doping preserved GeTe rhombohedral structure with slight X-ray diffraction peak shifts, implying material parameters variation. A doping model was proposed where three Bi atoms replaced the middle adjacent Ge sites of (001) plane, accompanied by two adjacent Ge vacancies right over Bi atoms. Ab initio calculations re-validated cell parameters change. Furthermore, Bi-doping process resulted in crystalline and amorphous state resistances increased by ∼2 orders, while a crystallization time dramatically reduced down to 50 μs, 20 times shorter compared to undoped nanowires.

Resistive switching near electrode interfaces: Estimations by a current model

The growing resistive switching database is accompanied by many detailed mechanisms which often are pure hypotheses. Some of these suggested models can be verified by checking their predictions with the benchmarks of future memory cells. The valence change memory model assumes that the different resistances in ON and OFF states are made by changing the defect density profiles in a sheet near one working electrode during switching. The resulting different READ current densities in ON and OFF states were calculated by using an appropriate simulation model with variation of several important defect and material parameters of the metal/insulator (oxide)/metal thin film stack such as defect density and its profile change in density and thickness, height of the interface barrier, dielectric permittivity, applied voltage. The results were compared to the benchmarks and some memory windows of the varied parameters can be defined: The required ON state READ current density of 105 A/cm2 can only be achieved for barriers smaller than 0.7 eV and defect densities larger than 3 × 1020 cm−3. The required current ratio between ON and OFF states of at least 10 requests defect density reduction of approximately an order of magnitude in a sheet of several nanometers near the working electrode.

Liquid flow-induced energy harvesting in carbon nanotubes: a molecular dynamics study

Energy harvesting by the flow of a hydrochloric acid-water solution through a carbon nanotube (CNT) is explored using atomistic simulations. Through ion configurations near the CNT wall, the ion drifting velocity is obtained, and the induced voltage along the axial direction is obtained as a function of key material and system parameters, including the applied flow rate, ambient temperature, solution concentration and nanotube diameter. The molecular mechanism of ion hopping and motion is elucidated and related to the variation of material and system parameters.

Thermal-Elastic-Plastic Finite Element Analysis for Laser Welding Deformation of Thin Plate

Thermal-Elastic-Plastic finite element analysis is introduced to study the deformation of laser welding of thin plate with consideration of varying material parameters. From aspects of numerical simulation and experiment, three welding cases are investigated: (1) the butt welding with constraint clamp, (2) the free bead welding, (3) the bead welding with constraint clamp. At last, the deformation configurations of welding plate under different constraint cases are characterized, and the behaviors of welding deformation are summarized.

Broadband High Directivity Multibeam Emission Through Transformation Optics-Enabled Metamaterial Lenses

A new broadband two- and three-dimensional, polarization independent coordinate transformation is introduced that is capable of mapping the radiation from an embedded omnidirectional source into any desired number of highly directive beams pointed in arbitrary directions. This transformation requires anisotropic materials, yet is spatially invariant and thereby can be readily implemented by currently existing metamaterial technologies. Moreover, the performance of the transformation is not sensitive to small material parameter variations, thus enabling a broad operational bandwidth. To validate the concept, a broadband 3-D coordinate transformation metamaterial lens fed by a simple monopole antenna was designed, fabricated and characterized, achieving a quad-beam radiation pattern over a 1.26:1 bandwidth with approximately 6-dB realized gain improvement in the $H$ -plane. In addition, the near-field coupling between the monopole and the lens was carefully tuned to accomplish a remarkable 70% broadening of the impedance bandwidth compared to the monopole antenna operating alone. It is also shown from the field simulations that the realized metamaterial lens provides both near-field and far-field 3-D collimating effects.

The theoretical radial stress solution and its experimental verification of expansion cement at annulus interfaces

Abstract To determine the initial loading state of the casing and cement sheath during cement setting, the theoretical solution of radial stresses at the annulus interfaces is derived considering volume expansion and material parameter variation. During the theoretical derivation, cement setting is divided into many time steps. In each step, the original radii of cement sheath without loading are calculated and the radial stresses are calculated according to the compatible deformation condition among the casing, cement sheath after free expansion and the stratum in this time step. The calculated radial stresses and radii of the cement sheath are used as initial data for the next step. The circumferential strains of casing and stratum are measured during cement setting process. The experimental result verifies the correctness of the theoretical solution. The calculated results and experimental data show that the radial stresses on both inner and outer boundaries of cement sheath are compressive stresses during the cement setting process, and their absolute values increase as the elastic modulus of the rock around the well increases. The higher the cement elastic modulus is, the larger the radial compressive stress on the wellbore will be. On the contrary, the radial compressive stress on the outer boundary of the casing will decrease. The cement material with appropriate elastic modulus should be adopted according to different elastic modulus of stratum, so as to realize loading equilibrium of the oil and gas well structural systems.

Effect of viscoplastic material parameters on polymer indentation

The effect of material parameters characterizing viscoplastic flow on the indentation response of polymers is investigated using three-dimensional finite element analyses and a one-dimensional expanding spherical cavity model. The polymer is characterized by a finite strain elastic–viscoplastic constitutive relation and two indenter shapes are considered; a conical indenter and a pyramidal indenter. The ability of the simpler expanding spherical cavity model to reproduce the trends obtained from the finite element solutions is assessed for both indenter shapes. Within the range of parameter variations considered, it is found that two material stress parameters characterizing the plastic flow resistance have the largest effect on the value of the indentation hardness although variations in other material parameters can lead to significant variations.