Typical Material Parameters Research Articles

Creep-induced subsidence along coastal Louisiana with GPS measurements and finite element modeling

Subsidence rates typically range between 2−7 mm/yr over the past one or two decades, as observed through GPS measurements at continuously operating reference stations along coastal Louisiana. The creep mechanism in Holocene sediments is adopted to quantitatively interpret the observed land subsidence along coastal Louisiana. An extended elasto-viscoplastic model is developed and implemented in ABAQUS. The material model is calibrated and validated based on both creep and constant rate of strain laboratory experiments conducted on Batiscan clays. Finite element models are then constructed to analyze creep-induced subsidence in Holocene sediments at four stations along coastal Louisiana. These models are calibrated with GPS-derived subsidence data to ensure consistency with measured values. Typical material parameters are used for lightly overconsolidated soils in the extended elasto-viscoplastic model. The modeled subsidence exhibits a negative correlation with both the initial overconsolidation ratio and strain-rate exponent. Subsidence accumulates over time at a decreasing rate. Creep-induced subsidence is predicted at four stations based on the calibrated finite element models, revealing an estimated 30.4 cm of subsidence over a span of 50 years (from 2005 to 2055) at station GRIS in Grand Isle. The significance of this study includes various aspects. The extended elasto-viscoplastic model improves the characterization of viscoplastic deformation in overconsolidated soils, typically associated with small strain rates (e.g., ɛ̇<10−8 s−1) observed in field measurements. The role of creep in subsidence in coastal Louisiana is confirmed, through a combination of GPS measurements and finite element modeling. The mechanism-based prediction of creep-induced subsidence can be applied to locations beyond coastal Louisiana.

Modelling the piezoelectric effect in a composite polymer film filled with disperse piezoelectric

Mesoscopic modelling of a composite material constituted by an electroneutral polymer (matrix) film filled with micropowder of piezoelectric ceramics (filler) is presented. The calculation scheme resembles that of the RVE (Representative Volume Element) method. The representative element (cell) is a right-angle prism with square cross-section, the height of which is equal to the film thickness. Around the midsection of the prism, there are a few (from 2 to 4) spherical piezoelectric particles positioned close to one another. The length of the base side of the prism is determined from the assumed solid phase content of the composite. To simulate the film, the cells are arranged in a continuous flat layer, inside which they are coupled by means of periodic boundary conditions imposed on their lateral surfaces. To reduce the artifacts of the model, the position of the center of each particle is chosen randomly within the area of the prism cross-section. In the framework of this approach, a low-density polyethylene film with embedded barium titanate particles is considered as an example. One of the surfaces of the film is fixed (no displacements), and the other one is left free. For the characteristics of the particles close to those used in the experiment and the typical matrix material parameters (elasticity moduli, Poisson coefficients, dielectric permittivity), the voltage output (piezoeffect) induced in the film in response to the uniform pressure applied to its free surface is evaluated. It is shown that the electric potential along the thickness of the film is nonuniform: it grows inside the particles and falls down in the interparticle gap. In order to present the results in the form applicative for comparison with the experimental data, for each variant of the system (number of the particles, weight fraction of the solid phase), the calculated values are averaged over a few tens of realizations of the particle positions inside the element.

Study on Deformation Characteristics of Diesel Engine Cylinder Liner under Different Influencing Factors

To study the influence of different influencing factors on the cylinder liner deformation characteristics, the finite element method was used to analyze the cylinder liner deformation under the pre-tightening condition of the diesel engine block-cylinder head assembly. Fourier spectrum, coaxiality, and main thrust surface inner diameter change were selected as deformation evaluation indicators to comprehensively evaluate cylinder liner deformation. The influence laws of several typical load parameters, structural parameters, and material parameters on cylinder liner deformation have been studied and sensitivity has been used to characterize the degree of influence of influencing factors on each deformation evaluation indicator. The research results can guide the evaluation and control of cylinder liner deformation under the pre-tightening condition.

Vibration mitigation in saturated soil by periodic in-filled pipe pile barriers

Abstract The complex dispersion relations and vibration mitigation properties of periodic in-filled pipe pile barrier in fluid-saturated poroelastic soil are investigated. The periodic structure theory is adopted and the viscosity of the in-filled materials is taken into account by using the Kelvin-Voigt model. The local resonance attenuation zones (LRAZs) covering the resonance frequency of the inner oscillator are obtained and then broadened by properly designing the viscosity of the in-filled materials. The influences of the typical geometry and material parameters of the pile barriers on the LRAZs are comprehensively studied. To validate the efficiency of LRAZs, the dynamic responses of a finite periodic pipe pile system are numerically simulated by conducting the time-history analysis. Taking the viscosity of the rubber into account, it is found that the attenuation parameter is suppressed in the LRAZs and enlarged outside of the LRAZs. In addition, the propagation of shear-waves can be effectively reduced in the LRAZs below 20 Hz when filling the pipe piles with soft materials. The findings of this study present a proper way to design periodic pipe pile barriers in saturated soil for ambient vibration attenuation, especially in the low-frequency range.

The direction of the d-vector in a nematic triplet superconductor

We investigate the states of triplet pairing in a candidate nematic superconductor versus typical material parameters, using the mean field theory for two- and three-dimensional tight-binding models with local triplet pairing in the Eu representation of the D3d, the point group of the system. In the two-dimensional model, the system favors the fully gapped chiral state for weaker warping or lower filling level, while a nodal and nematic state is favorable for stronger warping or higher filling, with the d-vector aligned along the principle axis. In the presence of lattice distortion, relative elongation along one of the principle axes, , tends to rotate the nematic d-vector orthogonal to , resulting in the nematic state at sufficient elongation. Three-dimensionality is seen to suppress the chiral state in favor of the nematic ones. Our results may explain the variety in the probed direction of the d-vector in existing experiments.

Correlation Study Between Material Parameters and Mechanical Properties of Iron–Carbon Compacts Using Sensitivity Analysis and Regression Model

Changing the material parameters such as powder characteristics and additives affects the final properties of an iron–carbon alloy. This study investigated the influences of three typical material parameters, iron particle size, graphite addition, and powder lubricant addition, on the density and mechanical properties of an iron–carbon alloy formed via powder compaction and sintering. Each material parameter was designed with five levels, and all of the powder mixtures were compacted under 500 MPa and sintered at 1120 °C for 30 min. The microstructure of the samples was observed for the green part and sintered part. Through the tensile test, yield strength, ultimate tensile strength, and elongation were measured. The tensile fracture surface was also examined to understand the changes in mechanical properties according to the parameters. The correlations between mechanical properties and material parameters were characterized by the mapping functions, and a sensitivity analysis was carried out to investigate which parameter had the larger influence on the mechanical properties. The results showed that graphite addition has the greatest influence on the mechanical properties due to the microstructural changes from hypoeutectoid structure to hypereutectoid structure. Further, a regression model was developed to describe the mechanical response of the iron–carbon alloy depending on the material conditions.

Antiferromagnet-based magnonic spin-transfer torque

In an antiferromagnet (AF) with uniaxial anisotropy, spin-up and spin-down magnons coexist and form an intrinsic degree of freedom resembling electrons. When polarized by an adjacent ferromagnet (F), a magnonic pure spin current can be thermally generated in an AF. We explore thermal magnon transport in an insulating F/AF/F trilayer where propagating magnons inside the AF spacer can transfer angular momenta between the two Fs. We find that a sufficiently large temperature gradient can switch the downstream F via magnonic spin-transfer torque if it is initially antiparallel with the upstream F. A reciprocal switching is achievable by reversing the temperature gradient. Using typical material parameters, we estimate the threshold to be less than 1 K/nm at room temperature, which can be reduced by raising temperature and enhancing the interfacial exchange coupling.

Wave dispersion analysis of multi-story frame building structures using the periodic structure theory

Introducing the periodic structure theory in the field of solid-state-physics into the field of civil engineering, this paper conducts a comprehensive theoretical and numerical study on the wave dispersion properties of multi-story frame building structures. At first, the theoretical infinite periodic model for the multi-story frame building structure is developed. Combining the Bloch-Floquet theorem and the State-Space-Transfer-Matrix-Method (SSTMM), the dispersion equation of the infinite periodic system is solved, from which dispersion curves and group/phase velocity curves of a practical multi-story reinforced concrete frame building structure are investigated. Second, a parametric study is performed to investigate the influences of the typical material parameters (density, strength grade of concrete), geometrical parameters (span length, floor height), theoretical simplified parameters as well as the damping parameter of frame building structures on the dispersion relations. Then, harmonic analysis and time history analysis are conducted to analyze the dynamic properties of the finite periodic frame structure in the frequency domain. Numerical results show that, when the main frequency region of the external excitations (like seismic waves) falls into the passing bands, dynamic responses of the multi-story frame building structure are very large; while the main frequency region of the external excitations falls into the attenuation zones, seismic responses of the multi-story frame building structure are very small.

Strain-induced chiral magnetic effect in Weyl semimetals

We argue that strain applied to a time-reversal and inversion breaking Weyl semi-metal in a magnetic field can induce an electric current via the chiral magnetic effect. A tight binding model is used to show that strain generically changes the locations in the Brillouin zone but also the energies of the band touching points (tips of the Weyl cones). Since axial charge in a Weyl semi-metal can relax via inter-valley scattering processes the induced current will decay with a timescale given by the lifetime of a chiral quasiparticle. We estimate the strength and lifetime of the current for typical material parameters and find that it should be experimentally observable.

Plasmon Dispersion at an Interface Between a Dielectric and a Conducting Medium With Moving Electrons

Dispersion of the plasmonic behavior at an interface between a dielectric and a conducting medium (e.g. metal, doped semiconductor, graphine, or superconductor) is studied considering the free electron gas in the conducting medium be moving along the interface. The derivation of the dispersion equation is provided, including the damping and the electrons drift. It is shown that the electrons behave as a compressible gas giving rise to new features and new surface plasmon wave solutions of the dispersion equation. A normalized form of the derived dispersion equation is obtained. It is then employed to study the general properties numerically using typical semiconductor material parameters found recently experimentally. Results are discussed in the light of possible novel applications of these physical effects such as, for example, plasmons propagation loss compensation.

Linewidth of power spectrum originated from thermal noise in spin torque oscillator

A theoretical formula for the linewidth caused by thermal activation in a spin torque oscillator with a perpendicularly magnetized free layer and an in-plane magnetized pinned layer was developed by solving the stochastic Landau–Lifshitz–Gilbert equation in the energy-phase representation. It is shown that the linewidth can be suppressed to 0.1 MHz by applying a large current (10 mA for typical material parameters). A quality factor larger than 104 is predicted in the large current limit, which is two orders of magnitude larger than a recently observed experimental value.

A parametric study of the Double-Ceramic-Layer Thermal Barrier Coating Part II: Optimization selection of mechanical parameters of the inside ceramic layer based on the effect on the stress distribution

The Double-Ceramic-Layer Thermal Barrier Coating (DCL-TBC) consists of a top ceramic layer, an inside ceramic layer, bond coat (BC) and alloy substrate. The introduction of TC2 has the effect of stress buffer to TC1, which causes the stress of TC1 decreased. In this situation, the typical material parameters ρ and E of the inside ceramic layer will have great influence on the stress distribution and ultimate life of the DCL-TBC. Based on this, the first part of the present paper is to investigate the effect of the typical material parameters ρ and E of the TC2 on stress distribution in the DCL-TBC with the thickness ratio of TC1 and TC2 as 150μm–150μm, using the finite element method. From mass calculation, the influences of the material parameters ρ and E upon the stresses of TC1 and TGO are presented in the paper.Secondly, the typical material parameters ρ and E of the TC2 is optimized and selected based on the optimization criteria which are “the stress of the TC1 is in safe state” and “the TGO has the lowest stress level”. Aiming at the criterion based on the safety of the TC1, “general safety region of E–ρ” and “E–ρ general safety boundary” are concluded in the stress map of E–ρ. Based on the criterion of the lowest stress level in TGO, it has been concluded that the point of 47.796–10.8029 is the best point of E–ρ, i.e. the DCL-TBC has the best life if the modulus E and thermal expansion coefficient ρ of the inside ceramic layer are 47.796GPa and 10.8029/°C(×10−6).

Computational model for determination of dynamic load capacity of large three-row roller slewing bearings

In the presented paper a calculation procedure for determination of dynamic load capacity of large three-row roller slewing bearings is presented. The calculation procedure consists of three main parts: (i) determination of internal contact force distribution in a large three-row roller slewing bearing with consideration of bearing clearances and ring support deformations, (ii) determination of stress field in the contact area between raceway and rollers as a consequence of contact forces and (iii) determination of the bearing’s fatigue life due to contact fatigue of the raceway. The internal contact force distribution is determined numerically by using a symmetry 3D FEM-model of a large three-row roller slewing bearing. Another numerical procedure is used to determine the stress field in the contact area between rollers and raceway. This problem is studied on different roller types: cylindrical roller (without profile correction), fully crowned roller (logarithmic-profile) and partially crowned roller (ZB-profile). Numerically determined contact stresses then serve as a basis for fatigue analyses, where the bearing’s service life of the bearing is determined by using the stress-life approach, considering typical material parameters of the bearing’s raceway.

Nanofluidic delivery of molecules: integrated plasmonic sensing with nanoholes

This article presents the detailed analysis of nanofluidics as a mechanism for the delivery of residual vapour/gas molecules in the air to nanoscale apertures in a porous metal or composite membrane with surface plasmons producing field hotspots near the apertures. Finite element analysis is used to calculate and to optimise the flow rate of air through apertures of different diameters with partial slip boundary conditions. Comparison of the calculated nanofluidic delivery rates with those due to diffusion of the tested residual molecules in the air is also conducted. Typical structural and material parameters at which either of these delivery mechanisms appears dominant are determined. Ways for further optimisation and enhancement of the operational capabilities of the described structures as nano-optical sensors and measurement techniques are also identified and discussed.

Self-consistent simulation of intermediate band solar cells: Effect of occupation rates on device characteristics

In order to design optimum structures for intermediate band solar cells, simulations based on self-consistent drift-diffusion model with a suitable treatment of the intermediate band in device domain are necessary. In this work, we have included the dependence of occupation rate of intermediate band at each position on optical generation rate via the intermediate band. Typical material parameters of GaAs were used except for the absorption coefficient of each corresponding band-to-band transition. Simulation results using our model indicate that the dependence of occupation rate on device position strongly affect short-circuit currents and also electrostatic potentials of the cell.

Faraday waves in smectic A liquid crystal layers

We studied with linear stability analysis the onset of parametric waves on the surface of asmectic A liquid crystal. For thin Sm-A layers under an applied static magnetic field thereare subharmonic–harmonic branches of surface waves at low modulating frequencyof the driving acceleration and long wavelength. A semi-infinite Sm-A mediumposes a dispersion relation with similar trends as for Newtonian liquids. Whenthe external forcing is negligible there are two damped surface waves excitedby thermal fluctuation of the interface, whereas in the absence of a magneticfield the dominant modes are of harmonic type for typical material parameters.

Flexoelectro-optic properties of chiral nematic liquid crystals in the uniform standing helix configuration

The flexoelectro-optic effect describes the rotation of the optic axis of a short-pitch chiral nematic liquid crystal under the application of an electric field. We investigate the effect in the uniform standing helix, or "Grandjean" configuration. An in-plane electric field is applied. The director profile is determined numerically using a static one-dimensional continuum model with strong surface anchoring. The Berreman method is used to solve for plane-wave solutions to Maxwell's equations, and predict the optical properties of the resulting structure in general cases. By using a chiral nematic with short pitch between crossed polarizers an optical switch may be generated. With no applied field the configuration is nontransmissive at normal incidence, but becomes transmissive with an applied field. For this case, numerical results using the Berreman method are supplemented with an analytic theory and found to be in good agreement. The transmitted intensity as a function of tilt, the contrast ratio, and the tilt required for full intensity modulation are presented. The angular dependence of the transmission is calculated and the isocontrast curves are plotted. For typical material and cell parameters a switching speed of 0.017 ms and contrast ratio of 1500:1 at normal incidence are predicted, at a switch-on tilt of 41.5 degrees. Experimental verification of the analytic and numerical models is provided.

Measuring the mechanical properties of human skin in vivo using digital image correlation and finite element modelling

The mechanical properties of the skin are important in many applications, but are not well understood. This paper presents a method for measuring the mechanical properties of human skin in vivo using digital image correlation, with a finite element model that was used to optimize the material properties to obtain the best match with the model data. The skin was modelled as an Ogden hyperelastic membrane, with a tension field wrinkling model and an initial stretch identified as an additional material parameter, and the boundary conditions were the measured load and the displacements around the edge of the region of interest. Fast, reliable convergence was obtained using a Hager–Zhang non-linear conjugate gradient solver. A stochastic optimization procedure was used to identify the material parameters. Good estimates of the material parameters could be obtained from the displacement field at a single time point. Typical material parameters were μ = 10 Pa, α = 26, and an initial strain of 0.2. These parameters were not unique; the stochastic optimization procedure gave good global convergence and an indication of the overall uncertainty in the identification of the results. It is argued that the use of the DIC technique, which generates very large amounts of data, also gave a clearer picture of the overall uncertainty.

Modeling of Resin Flow in Reinforced Dielectric Prepregs

Manufacturing of printed circuit boards or chip-packaging substrates involves the use of resin-filled reinforcement materials, known as prepregs, to bond together laminates with patterned copper layers and serve as dielectric material. In the circuit board or substrate lamination process, the prepreg sheet is placed on top of the conductive copper patterns and pressure is applied to squeeze the resin out of the prepreg to flow and fill the gaps between the baseboard and the copper as well as drilled holes and vias. The primary processing requirement is for resin to fill all the gaps within reasonable time and pressure limits, before the resin cures to a hardened thermoset material. As the resin flow path may be nontrivial, it is desirable to model resin flow and filling of the gap as a function of applied pressure and lamination press closing rate so that one can successfully manufacture a variety of circuit board designs with different material systems. In this work, we model the flow during the filling of the gaps and justify noteworthy simplifications to provide a solution in closed form. This allows us to relate the material and process parameters such as prepreg thickness and applied pressure to the circuit board design. It also permits prediction of the transient development of gap filling. We illustrate the factors that influence the flow and fill process and discuss their importance. Finally, we analyze the process with typical material and processing parameters and compare it with laboratory scale and industrial experiments.

Toward an Understanding of Controlling Parameters in Softwood and Hardwood Pellets Production

Production of biofuel pellets from hardwood, such as beech, is often very troublesome as observed in large-scale pellet production plants, where reduction of capacity and frequent blocking may be experienced. The problems may be reduced through a laborious optimization procedure of the process conditions and the utilization of softwood and adhesive materials. To optimize and facilitate such a procedure, a deeper understanding of the fundamental physical−chemical mechanisms that control the pelletizing process is sought after by combining small-scale experiments and an advanced pellet production model. Mixtures of beech rich in corrosive alkali chloride salt, pine softwood, brewers spent grains (BSG), and inorganic additives are experimentally tested using a small-scale pellet mill. It was possible to pelletize a beech/pine mixture containing up to 40% (wt) beech. The addition of 15% (wt) BSG to the beech dust significantly facilitated the pelletizing process. The addition of necessary inorganic anti-slag and anti-corrosive compounds into pellets made of beech may enhance the problems in an unpredictable way. However, if the inorganic additives are added directly into BSG before mixing it with the beech dust, the material can easily be pelletized. A pellet production model is developed that describes the pelletizing pressure variation along the press channels of the matrix. Equations based on differential control volumes are set up to describe the forces acting on the pellet in the matrix. Important model parameters are the sliding friction coefficient, the ratio of compression, and the material-specific parameters, such as the elastic modules and Poisson's ratio. Model calculations show how the variation in the model parameters significantly changes the necessary pelletizing pressure. Using typical material parameters of beech and pine, it is illustrated why beech, in accordance with the experimental test results, is more difficult to pelletize than pine.