Values Of Material Parameters Research Articles

X-ray reflectivity data analysis using Bayesian inference: The study of induced Pt magnetization in Pt/Co/Pt

The induced Pt magnetization in a Pt/Co/Pt thin film structure is studied. The normally nonmagnetic Pt acquires a magnetic moment due to the magnetic proximity effect at the Co–Pt interfaces. Element specific Pt structural and magnetic properties are characterized by synchrotron-based resonant x-ray reflectivity and x-ray resonant magnetic reflectivity measurements. An advanced analysis method based on Bayesian inference is used for model fitting of the x-ray data. Using this method, we retrieve the best fit values of material parameters (e.g., thickness, interfacial roughness) from the data. Analysis of x-ray reflectivity data of this specific system shows that the Pt magnetization and Co–Pt interfacial roughness is significantly different between the top and bottom Pt layers, with both values being larger in the top Pt. The successful application of this Bayesian method to study the magnetic and structural properties of a thin film system demonstrates its effectiveness for x-ray reflectivity data analysis.

Electric properties of olive oil under pressure

The main purpose of the experiment was a thermodynamic research with use of the electric methods chosen. The substance examined was olive oil. The paper presents the resistance, capacitive reactance, relative permittivity and resistivity of olive. Compression was applied with two mean velocities up to 450 MPa. The results were shown as functions of pressure and time and depicted on the impedance phase diagram. The three first order phase transitions have been detected. All the changes in material parameters were observed during phase transitions. The material parameters measured turned out to be the much more sensitive long-time phase transition factors than temperature. The values of material parameters and their dependence on pressure and time were compared with the molecular structure, arrangement of molecules and interactions between them. Knowledge about olive oil parameters change with pressure and its phase transitions is very important for olive oil production and conservation.

Bio-convective micropolar nanofluid flow over thin moving needle subject to Arrhenius activation energy, viscous dissipation and binary chemical reaction

The study of nanofluid dynamics considering the bioconvection effects has significant applications, because nanofluid has remarkable capabilities for thermal transportation in comparison with pure fluids in various industrial and engineering applications. Keeping in view, such incredible characteristics the main objective of this work is to examine the influence of bioconvective micropolar nanofluid flow over a thin moving needle comprising of gyrotactic microorganism. The flow is also exposed to Arrhenius activation energy, binary chemical reaction and viscous dissipation. The governing equations are transformed to a dimensionless form by making use of a set of suitable variables and solved afterwards by employing homotopy analysis method (HAM). As main outcomes it is established in this work that, flow profiles decline with growing values of buoyancy ratio parameter, material parameter, volume fraction and bioconvection Rayleigh number. Thermal profile grows up with higher values of volumetric fraction, Brownian motion, Eckert number and thermophoretic parameter. Concentration profiles decline with growing values of thermosphoretic parameter, Brownian motion, Lewis number, chemical reaction parameter and grow up for increasing values of activation energy parameter. Moreover, a fine agreement between current results and the results available in literature has also established in current work.

Phenomena of Bifurcation and Chaos in the Dynamically Loaded Hyperelastic Spherical Membrane Based on a Noninteger Power-Law Constitutive Model

The phenomena of bifurcation and chaos are studied for a class of second order nonlinear nonautonomous ordinary differential equations, which may be formulated by the nonlinear radially symmetric motion of the dynamically loaded hyperelastic spherical membrane composed of the Rivlin–Saunders material model with a noninteger power-law exponent. Firstly, based on the variational principle, the governing equation describing the problem is obtained with the spherically symmetric deformation assumption. Then, the dynamic characteristics of the system are qualitatively analyzed in detail in terms of different values of material parameters. Particularly, for a given constant load, the parameter spaces describing the bifurcation behaviors of equilibrium curves are established and the characteristics of equilibrium points are presented; for a periodically perturbed load, the quasi-periodic and chaotic behaviors are discussed for the systems with two and three equilibrium points, respectively.

Systematic selection of field response measurements for excavation back analysis

In a geotechnical excavation, back analyses are routinely performed using the measured field responses to derive the material parameter values for the different soil layers present at the site. For the purpose of back analyses, the engineers will usually make use of a portion of the large volumes of field data collected, in order to keep the computational effort to a manageable level. However, excavation back analyses using different selected sets of field response measurements may not yield the same knowledge of material parameter values. Therefore, measurements need to be carefully selected to obtain the best estimates of material parameter values. Currently, the selection of measurements is largely based on engineering heuristics; no method has been proposed to systematically quantify the expected knowledge of the parameter values that field response measurements could provide. In this paper, a hierarchical algorithm based on a joint-entropy objective function is proposed to systematically evaluate the knowledge gained from wall deflections measured by eight inclinometers at an excavation site. The algorithm ranks the inclinometers based on the expected knowledge yield of the parameter values. Back analysis using actual field response measurements is then carried out to corroborate the ranking. The rankings obtained from the back analysis results and the predictions of the hierarchical algorithm are very similar, which suggests that the latter method can aid in the judicious selection of field response measurements in order to obtain useful knowledge of material parameter values. Since the application of the hierarchical algorithm does not entail the use of actual measurements, such predictions can be made at the early stages of a project, even before the commencement of site activities.

A Parameter Sensitivity Study of Solid Oxide Fuel Cells Based on One-dimensional Model

Solid oxide fuel cells (SOFCs) are promising and efficient energy conversion devices. The modeling method was widely used to study characteristics of SOFCs due to limitation of experiments. Values of material properties such as porosity, tortuosity and pore radius are required information in modeling. Current modeling works usually employ material properties used in the literature, which are not exactly measured and the values vary in wide ranges. However, inappropriate selection of material properties can result in incorrect modeling results of SOFCs. In this study, a one-dimensional model of SOFCs was established to analyze the effects of different material parameters on the modeling results. A parameter sensitivity analysis was also conducted to determine the most influential parameters on the polarization curve. The results provide a reference for selection values of SOFC material parameters. This work can also be used as a guideline to fit the experimental polarization curve in numerical simulations by adjusting appropriate material parameters.

Rock slope stability charts based on limit equilibrium method incorporating Generalized Hoek–Brown strength criterion for static and seismic conditions

Stability charts present a graphical approach for the estimation of factor of safety (FOS) of a finite slope with uniform soil properties which are routinely used by geotechnical engineers. They provide a way for quick and efficient determination of stability of slopes sidestepping the need for carrying out actual analysis. In the present work, authors have developed stability charts of rock mass to determine global minimum FOS for rock slope stability problems. The rock mass is modelled by incorporating generalized Hoek–Brown strength criterion proposed by Hoek et al. (Hoek–Brown criterion—2002 edition, 2002). Limit equilibrium technique based Morgenstern and Price (Geotechnique 15:79–93, 1965) method is used to determine the value of factor of safety of the rock slope against failure. An evolutionary optimization method i.e. Particle swarm optimization (PSO) is used to search for the minimum FOS values and the associated critical failure surface out of all possible slip surfaces. A MATLAB code has been developed for this purpose. The charts have been developed for the entire range of Geological Strength Index (GSI) values ranging from 0 to 100 for intact rock mass characterized by the disturbance factor D = 0 for both static and seismic loading conditions. The seismic slope analysis is performed by an equivalent static method using a horizontal seismic coefficient (kh) with values ranging from 0.10 to 0.30. Stability charts contain stability numbers which are inversely proportional to FOS value of the slope. In the present work, stability numbers are plotted for different inclination angles ( $$\beta$$ ) equal to 15°, 30°,45°, 60° and 75+°, respectively, for both static and seismic conditions considering the variations of other material parameters such as $$m_{i}$$ and $${\text{GSI}}$$ . Stability numbers are observed to increase with an increase in angle of inclination ( $$\beta$$ ) of the slope and correspondingly FOS values follow a decreasing trend. However, stability numbers follow a decreasing pattern with increasing values of material parameters $$m_{i}$$ and $${\text{GSI}}$$ designating improved rock quality with corresponding increase in FOS values of the rock slope.

Mathematical modelling of unsteady solute dispersion in two-fluid (micropolar-Newtonian) blood flow with bulk reaction

A mathematical model is developed for hemodynamic transport of a reactive diffusing species e.g., oxygen in a rigid artery under constant axial pressure gradient and undergoing a first-order chemical reaction with streaming blood. A two-fluid model is deployed where the core region is simulated as an Eringen micropolar fluid, and the plasma layer engulfing the core, i.e., near the boundary, is analyzed as Newtonian viscous fluid. Closed-form solutions are presented for the velocity and micro-rotation profiles, and a Gill decomposition method is deployed for the concentration field. Expressions are derived for the dispersion coefficient, mean and transverse concentration. Transverse concentration is observed to be enhanced with increasing micropolar coupling number (N) and reaction rate (β); however, it is reduced with greater micropolar material parameter (s) and viscosity ratio (λ). Axial mean concentration peaks are reduced in magnitude and displaced further along with the arterial geometry with greater micropolar material parameter values, whereas the opposite effect is induced with greater micropolar coupling number. The study is relevant to hemorheology, diseased arteries and coagulating hemodynamics and may help physiologists in furnishing a more refined understanding of diffusion processes in cardiovascular hydrodynamics.

Substrate design to minimize residual stresses in Directed Energy Deposition AM processes

This paper proposes a strategy to optimize the design of the substrate structures used in Additive Manufacturing (AM) by Directed Energy Deposition (DED) to minimize the residual stresses induced by this fabrication process. To this end, several numerical analyses were performed to analyse different substrate designs in order: (i) to reduce the sensitivity to the initial non-steady stage when the first layers of material are deposited, (ii) to optimize the heat flux through the substrate to reduce the Maximum Temperature Gradients (MTG) and, (iii) to modify the substrate stiffness and its mechanical constraining to the thermal deformations during the building process and the cooling phase. To ensure the reliability of the numerical simulations, an in-house software is calibrated to allow for an accurate analysis of DED. Thus, an experimental setting is undergone to feed the numerical model with suitable values of both material and process parameters through temperature and displacement measurements and numerical fitting. Once calibrated, the software is used to evaluate the performance of several substrate designs to mitigate the residual stresses induced by the DED process. A thin-walled rectangular part selected as industrial demonstrator showed a significant reduction (up to 62%) of the maximum tensile stresses.

Diffusion transport over grain-boundary barriers as the origin of N1 deep level transient spectroscopy signal in [formula omitted] solar cells

In this work, we explore the hypothesis that the N1 peak in Cu(In,Ga)Se2 (CIGS) solar cells is caused by secondary barriers. We indicate, through numerical modelling of the corresponding Deep Level Transient Spectroscopy (DLTS) signal, that these barriers may be located at grain boundaries. Moreover, the proper reconstruction of the N1 signal using the double-barrier model requires an assumption that corresponding capacitance transients are due to the diffusion limited transport of holes over grain boundaries. Only then we were able to achieve sufficiently small values of the saturation current for realistic values of material parameters. We show that the position of the N1 DLTS peak and its activation energy depends on the effective density and the effective mobility of holes which can be calculated based on grain size and the properties of grain boundaries. This interpretation opens a room for the explanation of the unusual properties of the N1 signal in CIGS solar cells.

Mechanical Properties of Bridge Steel from the Late 19th Century

This article presents the results of testing of the strength of structural steel taken from a railway bridge. It was built within the borders of today’s Poland during the late 19th century and was in use for over 100 years, until the early 21st century. The main mechanical parameters of the bridge steel, such as its static and impact strength were determined. The results of the analysis of fracture surfaces with the aim of the identification of the material’s macrostructure are also presented. This article discusses the findings and analyses the values of material parameters in the context of requirements resulting from existing standards, and compares the results with those obtained during the testing of bridge steels of a similar age and operational period.

Periodic response of a nonlinear axially moving beam with a nonlinear energy sink and piezoelectric attachment

An efficient semi-numerical framework is used in this paper to analyze the dynamic model of an axially moving beam with a nonlinear attachment composed of a nonlinear energy sink and a piezoelectric device. The governing equations of motion of the system are derived by using the Hamilton’s principle with von Karman strain-displacement relation and Euler - Bernoulli beam theory. The nonlinear energy sink is modeled as a lumped - mass system composed of a point mass, a spring with nonlinear cubic stiffness and a linear viscous damping element. The piezoelectric device is placed in the ground configuration. Frequency response curves of the presented nonlinear system are determined by introducing the incremental harmonic balance and continuation method for different values of material parameters. Based on the Floquet theory, the stability of periodic solutions was determined. Moreover, the presented results are validated with the results obtained by a numerical method as well as the results from the literature. Numerical examples show a significant effect of the nonlinear attachment on frequency response diagrams and vibration amplitude reduction of the primary beam structure.

A fully coupled damage model with stress triaxiality and Lode dependence

In the present work, an advanced CDM model considering stress triaxiality and Lode angle effect is proposed. The framework of thermodynamics of irreversible processes with state variables is used to build the constitutive equations accounting for strong and full coupling between all the dissipative phenomena. The proposed model is implemented into Finite Element (FE) code ABAQUS/Explicit via a user material subroutine (VUMAT). A detailed parametric study with various values of the new material parameters is conducted in order to show the predictive capability of the proposed model. Applications to sheet metal forming simulation have been performed to validate the damage prediction capability of the proposed model, and the numerical simulation results are analysed and discussed.

Editorial for the special issue on advances in forward and inverse surrogate modeling for high‐frequency design

Editorial for the special issue on advances in forward and inverse surrogate modeling for <scp>high‐frequency</scp> design

Mathematical analysis of a non-Newtonian polymer in the forward roll coating process

Abstract This article describes the development of a mathematical model of forward roll coating of a thin film of a non-Newtonian material when it passes through a small gap between the two counter-rotating rolls. The conservation equations of mass, momentum, and energy in the light of LAT (lubrication approximation theory) are non-dimensionalized and solutions for the velocity profile, flow rate, pressure distribution, pressure, forces, stresses, power input to the roller, and temperature distribution are calculated analytically. It is found that by changing (increasing/decreasing) the value of material parameters, one can really control the engineering parameters like, stress and the most important the coating thickness and is a quick reference for the engineer working in coating industries. Some results are shown graphically. From the present study, it has been established that the material parameter is a device to control flow rate, coating thickness, separation points, and pressure distribution.

Numerical and experimental analysis of fretting fatigue performance of the 1350-H19 aluminum alloy

When power transmission cables are subjected to oscillatory displacements, due to the wind vibration, fretting fatigue phenomenon takes place, being the main prompter of catastrophic failure. In this work, we investigate the behavior of an 1350-H19 aluminum wire, that is a structural element of the IBIS (ACSR 397.5 MCM) conductor cable, when subjected to fretting fatigue. For this, a numerical methodology was developed, in which a three-dimensional finite element model was constructed to obtain the maximum Von Mises stresses in the vicinity of the wire-to-wire contact. Thus, a stress-based uniaxial fatigue approach was implemented, resulting in S–N curves. The effect of mean stresses on fatigue behavior was also considered through a series of well-known models. The data generated in this process were validated with experimentally obtained S–N curves on a MTS 322.21 machine, especially modified for this purpose. Most of the results were within the limits considered, with slightly conservative tendencies. A new value of adjustable material parameter has been proposed to be used with Walker’s model, increasing the accuracy of the predictions.

Analysis of three-dimensional bending deformations and failure of wet and dry laminates

For given mechanical properties of the fiber and the matrix, and their volume fractions, we first numerically, using the finite element method, find values of the elastic moduli and the diffusivity of the homogenized unidirectional (UD) lamina. However, values of material parameters appearing in the Hashin failure criteria for a lamina and in the cohesive zone model for simulating delamination between adjacent plies, the coefficient of swelling (or hygral expansion), and of the reduction in values of parameters upon full saturation with water are taken from the literature. Using these values, we analyze 3-dimensional hygro-mechanical deformations of dry and fully saturated UD and cross-ply (CP) laminates for a 3-point bending configuration, and delineate differences in failure mechanisms of dry and wet laminates. It is found that, at full saturation, the hygral stresses are negligible in UD laminates but alternate between compressive and tensile values of large magnitude in the CP laminate. Furthermore, the hygral stresses are found to suppress failures in some regions but facilitate in other parts of the laminates. During displacement controlled simulations, the maximum load at the mid-span of wet laminates is found to be about 30% less than that for the corresponding dry laminates, delamination induced between adjacent plies of a laminate causes noticeable sliding between them, and warping near the laminate corners.

Magnetic field effect on piezo-thermoelastic wave propagation in a half-space within dual-phase-lag

The current work is concerned with the study of wave propagation in a half-space of a piezo-thermoelastic material under a bias tangential magnetic field within dual-phase-lag (DPL). This is relevant to the design and performance of piezoelectric devices working under a bias magnetic field, for example, the DC magnetic field piezoelectric sensors widely used in various areas of technology. The characteristic time for the problem under consideration is in the range of picoseconds, which is comparable to the thermal relaxation times in many metals. Exact analytic expressions for the mechanical displacement, temperature, stress, electric potential, electric displacement, electric current and induced magnetic field are obtained using normal mode analysis. Plots are provided and discussed for rather large intensities of the magnetic field. Comparison is carried out between the results predicted by DPL and Lord–Shulman theory (LS) in the presence or absence of magnetic field. The presented results clearly indicate that the effect of magnetic field is more pronounced for LS than for DPL. It was found that for magnetic field intensities of $$10^7$$ Tesla, both theories give almost identical results. Beyond this threshold value, sensible deviations between the theories start to appear and grow with the intensity of the magnetic field. In connection with experimental measurements, the present investigation may help in calculating numerical values of different material parameters and in assessing the efficiency of the two considered theories.

Frequency-dependent dielectric response of ferroelectric–dielectric junction with negative electric capacitance

We calculated the frequency dependent dielectric response (electric susceptibility) of layered ferroelectric-dielectric junction, biased by the time-dependent harmonic voltage with single frequency $\omega$. Working point is stabilized, by the charge boundary condition between the layers, in the region with negative electric capacitance. The static susceptibility $\chi_0$ is negative and relative dielectric constant $\epsilon_r$ smaller than one, clearly indicating the opposite direction of electric field and polarization in the ferroelectric layer due to the negative electric capacitance. At finite frequencies this sign is preserved in real part of susceptibility which gains the frequency dependence. Also, frequency dependent imaginary part arises due to the phase shift between electric field and polarization. The type of that frequency dependence in linear regime is so-called relaxation (Debye) response, i.e. $\chi'(\omega)=\chi_0/(1+(\tau \omega)^2)$ and $\chi"(\omega)=\chi_0\tau \omega/(1+(\tau \omega)^2)$, where $\tau$ is polarization switching time characteristic to ferroelectric material. In particular, we modeled the junction of ferroelectric BaTiO$_3$ and dielectric Al$_2$O$_3$, taking the experimental values of material parameters, and addressed the role of nonlinearity with respect to result of the linear response theory.

Optimum First Failure Loads of One- and Two-Core Doubly Curved Sandwich Shells

For fixed values of the areal mass density, product of the midsurface curvilinear lengths, and the choice from three unidirectional fiber (glass, graphite, or aramid) reinforced composites for facesheets, one- and two-core doubly curved sandwich shell’s geometries, fiber material, and fiber orientations for the facesheets are found that maximize the first failure load. Also determined are the locations of failure points and stress components significantly contributing to the failure, as well as the effects of uncertainties in values of material parameters on the failure load. The shell’s quasi-static and infinitesimal deformations are analyzed with a third-order shear and normal deformable plate/shell theory, in-plane stresses are found by using the plate theory deformations and transverse stresses using a one-step stress recovery scheme. The Tsai–Wu failure criteria, and honeybees inspired nest-site selection optimization algorithm are employed. Effects of uncertainties in material parameters are quantified by the Latin hypercube method and a statistical software, JMP. The predicted failure load and the failure point location agree well with their experimental values. It is observed that the first failure occurs in a core (facesheet) due to the transverse shear stress (in-plane transverse axial stress) exceeding its critical value. The methodology can be used to design the minimum weight optimal doubly curved multicore sandwich shells.