Multiphysical Effects Research Articles

Modeling of flash sintering of ionic ceramics

A fundamental understanding of the influence of defects in ionic ceramics at the atomic, microstructural, and macroscopic levels, before, during, and after the flash sintering event is key to the development of ceramic processing operations that lead to fast, low cost, and environmentally safe fabrication of materials. The observed phenomenology of the flash process encompasses multiple time and length scales and has resulted in a wide variety of what sometimes appears to be contradictory explanations. This article summarizes the latest developments on the modeling and simulation of flash sintering, specifically those related to the understanding of the equilibrium and kinetic properties and the corresponding microstructural evolution of ionic ceramics. Challenges and opportunities in the development of theoretical analyses that include unidentified multiphysical effects are discussed, as they pertain to the processing of technologically relevant ceramic materials for advanced structures and devices.

Novel magnetoresistance explorations and multistate data storage applications

Novel spintronic devices with low power consumption, nonvolatility, and high storage density are highly desired to meet the rapid development of modern information storage and communication technology, which poses a great challenge to both material and device researches. To overcome this challenge, our group has focused our research on the following two aspects. On one hand, we have explored novel magnetoresistance effects in a variety of materials and devices, aiming to get a deep understanding about the spin dependent transport and obtain an effective control of spin-dependent transport. On the other hand, we have tried to control the magnetoresistance based on multi-physical field effects, aiming to obtain spintronic prototype devices that can be used for multi-state data storage. Regarding the novel magnetoresistance explorations, this article will introduce: (1) The negative magnetoresistance in amorphous condensed magnetic semiconductors. The spin dependent variable range hopping model is proposed, which can quantitatively explain the temperature and magnetic field dependent transport behavior in the condensed magnetic semiconductors. In addition, this model provides an alternative way to detect the spin polarization ratio of the magnetic semiconductors. (2) The positive magnetoresistance in single-crystal CoZnO magnetic semiconductors. By quantitative analysis of the transport properties of CoZnO films, it is observed that the positive magnetoresistance in the “hard gap” regime is the result of the carrier wavefunction shrinkage under applied magnetic field. (3) The rectification magnetoresistance in non-magnetic Schottky heterojunctions and the tunneling rectification magnetoresistance in magnetic tunnel junctions. A brand new rectification magnetoresistance is observed in nonmagnetic Al/Ge Schottky heterojunctions: The application of a pure small sinusoidal alternating current to the nonmagnetic Schottky heterojunctions can generate a significant direct-current voltage, and this rectification voltage strongly varies with the external magnetic field. Moreover, by using CoO-ZnO composite tunneling barrier, the charge-related rectification and spin-dependent tunneling magnetoresistance are integrated into the Co/CoO-ZnO/Co magnetic tunneling junctions to realize the tunneling rectification magnetoresistance. The observation of rectification magnetoresistance and tunneling rectification magnetoresistance not only adds new members to the magnetoresistance family, but also provides a promising way to control the devices’ properties by using alternating current. In terms of multistate data storage application, this review will introduce: (1) The electrical and magnetic field controllable 4 resistance states in oxide heterojunctions. In Co/CoO-ZnO/Co magnetic tunneling junctions, by integrating the electrical field induced resistance switching and the magnetic field induced tunneling magnetoresistance effects, four nonvolatile resistance states are demonstrated. (2) The remanent magnetization controllable 10 resistance states in magnetic heterojunctions. Here, a general remanent magnetism engineering method is proposed for realizing multiple reliable magnetic and resistance states, not depending on a specific material or device structure. Especially, as a proof-of-concept demonstration, ten states of nonvolatile memory based on the manipulation of ferromagnetic remanent magnetization have been revealed in both Co/Pt magnetic multilayers with strong perpendicular magnetic anisotropy and MgO-based magnetic tunneling junctions at room temperature. (3) The spin-orbit torque controllable 10 resistance states in single-layer magnetic alloy. A repeatable bulk spin-orbit torque switching of the perpendicularly magnetized CoPt alloy single-layer films is realized by introducing a composition gradient in the thickness direction to break the inversion symmetry. Moreover, a ten states nonvolatile memory is illustrated solely by changing the electrical current to control the multi-domain states of the CoPt alloy.

A Transient 3-D Thermal Modeling Method for IGBT Modules Considering Uneven Power Losses and Cooling Conditions

Junction temperature is a key parameter for the safe operation of power semiconductor devices in power electronic systems. However, it is difficult to forecast the accurate thermal stress of the device in field use. Consequently, engineers tend to use higher rated devices to maintain excessive margin, resulting in a higher cost. In this article, a transient 3-D thermal modeling method for insulated gate bipolar transistor (IGBT) modules is proposed to obtain accurate temperature distribution considering uneven power losses and cooling conditions. The analytical model of uneven switching energy losses among the parallel IGBT chips in modules is built according to the analysis of device simulation results. The effect of uneven cooling conditions on temperature distribution in IGBT modules is considered by thermal-fluid cosimulation. Furthermore, a hybrid simulation strategy is proposed to obtain the transient thermal behavior in three dimensions. Through appropriate interface design, the power loss model is connected with the finite element model to achieve field-circuit cosimulation with multiple time steps, which takes full consideration of the multiphysical coupling effects among power loss, temperature, and flow fields. Finally, the thermal stresses of IGBT modules under different operating conditions are forecast by the proposed method.

Computational thermomechanics for crystalline rock. Part II: Chemo-damage-plasticity and healing in strongly anisotropic polycrystals

We present a thermal–mechanical–chemical-phase field model that captures the multi-physical coupling effects of precipitation creeping, crystal plasticity, anisotropic fracture, and crack healing in polycrystalline rock at various temperature and strain-rate regimes. This model is solved via a fast Fourier transfer solver with an operator-split algorithm to update displacement, temperature and phase field, and chemical concentration incrementally. In nuclear waste disposal in salt formation, brine inside the crystal salt may migrate along the grain boundary and cracks due to the gradient of interfacial energy and pressure. This migration has a significant implication on the permeability evolution, creep deformation, and crack healing within rock salt but is difficult to incorporate implicitly via effective medium theories compared with computational homogenization. As such, we introduce a thermodynamic framework and a corresponding computational implementation that explicitly captures the brine diffusion along the grain boundary and crack at the grain scale. Meanwhile, the anisotropic fracture and healing are captured via a high-order phase field that represents the regularized crack region in which a newly derived non-monotonic driving force is used to capture the fracture and healing due to the solution–precipitation. Numerical examples are presented to demonstrate the capacity of the thermodynamic framework to capture the multiphysics material behaviors of rock salt.

A curing model for the numerical simulation within additive manufacturing of soft polymers using peridynamics

Within this paper, the modelling and simulation of extrusion-based Additive Manufacturing (AM) processes of curing polymers is presented. The challenge of the AM is the adjustment of processing parameters. This includes the application of laser radiation to locally accelerate the curing in order to control the final geometry of the implant. Since complex multi-physical coupling effects are hardly predictable by operator experience, numerical simulations are beneficial. When the underlying physical effects of the AM processes are captured correctly within the simulations, a realistic representation of the process is possible. To model the material behaviour during the process, a process-dependent large strain curing model is formulated, considering the stress free curing behaviour of the material. State-of-the-art models are not able to model the fluid-like behaviour of low cured polymers. This needs a formulation that takes into account finite deformations. Hence, the current model is extended to finite plasticity using a process-dependent yield function. This allows the modelling of material spreading in the fluid-like state by simultaneously reducing the accumulation of elastic stored energy, which would lead to an unintentional and non-physical bounce-off behaviour otherwise. For the numerical simulations, an enhanced version of the peridynamic correspondence formulation using fractional subfamilies with associated volume weighting factors is introduced and implemented. Besides the specific laser modelling as a volumetric heat source, a local–non-local coupling of the arising thermo-chemo-mechanical coupled equations is introduced within the peridynamic framework. Within the simulations, the applicability of the plasticity-based approach to model material spreading in the fluid-like state is presented. Finally, the software for extrusion-based printing processes is developed and the complete thermo-chemo-mechanical coupled AM process is simulated. It is shown that higher geometrical precision is obtainable in terms of a reduced material spreading by the application of a laser radiation. The model constitutes the first step of the virtual implant development regarding the optimisation possibilities during the AM process.

Understanding lightning strike induced damage mechanism of carbon fiber reinforced polymer composites: An experimental study

To date, the predictive analysis of lightning-induced damage of carbon fiber reinforced polymer composites (CFRP) is challenging due to the complex multi-physical coupling effects. The current study aims to clarify the lightning-induced damage mechanism of CFRP and improve the lightning protection systems for aerospace applications. Herein, an artificial lightning strike experiment was designed to simulate the real-life conditions and investigate the influence of lightning strike on a quasi-isotropic CFRP sample. The lightning strike and corresponding degradation process were observed by using a high-speed camera and infrared thermal imaging. Moreover, lightning-induced damage was assessed by visual inspection and non-destructive testing. The damage behavior of CFRP composites was deduced by analyzing the lightning process and damage modes. The results reveal that the damage is caused by the electro-thermo-mechanical response due to lightning arc flow and Joule heating ablation due to the conductive nature of the CFRP composites. The current work provides an enhanced understanding of the failure mechanism under lightning strike and outlines instructional suggestions to refine the numerical model of lightning-induced damage of CFRP for further study.

Toward a Robust Design of an Aileron Electromechanical Actuator: Sensitivity Analysis and Parametric Tolerancing Using a Variational Approach

For a mechatronic system, the lack of robustness is mainly due to an ignorance of variability, which is unavoidable in every designed system at all stages of system development and during its life cycle. In fact, the inherent imperfections of manufacturing processes and operational variations such as material wear or multiphysical effects (thermal, vibrations, etc.) involve parametric variations, which can degrade the proper system function. To ensure a high level of quality and to improve design robustness, the deviations between actual and target definition should be restricted by specified tolerances. Moreover, it is important to understand the relationship between parameter deviations and system behavior. Thus, in this article, a variational approach is proposed to identify performance sensitivity to parameter deviations in a mechatronic system and to determine influential parameters that affect significantly the proper functioning of the system and its behavior. Furthermore, this approach is used to specify the admissible parameter deviations for which the given specifications can be guaranteed. The complete approach is applied to an example in the aeronautic field: an electromechanical actuator driving an aircraft primary flight control surface (aileron).

Comparison and parametric study of two theoretical modeling approaches based on an air-to-water thermoelectric generator system

Numerical model and thermal resistance model are two commonly used modeling approaches to analyze the performance of thermoelectric devices. However, a great number of assumptions and simplifications are made in previous researches. This work presents a steady state and fluid-thermal-electric multi-physical numerical model and improves the conventional thermal resistance model to investigate the performance of an air-to-water thermoelectric generator system. In considering the multi-physical field coupling effects and temperature dependent thermoelectric material properties, the comparison of these two theoretical models and parametric investigation on the thermoelectric generator system are conducted. The results indicate that the thermal resistance model can be used to preliminarily evaluate the performance of thermoelectric generator system with acceptable accuracy at appropriate working conditions, but more precisely, the numerical model should be adopted. Besides, the heat losses should not be omitted in the theoretical analysis, and an optimal load resistance must be chosen between the maximum power one and the maximum conversion efficiency one. The findings of this work can guide the future theoretical analysis of the thermoelectric generator system by numerical model or thermal resistance model.

Optical-force-directed single-particle-based track etching in polystyrene films

The establishment of optical trapping theory by A Ashkin almost half a century ago led to the trapping and manipulation of micro-/nano-objects and atoms by laser beams, which is now applied in many fields. However, in a complex system where multi-physical effects interact synergistically, light–matter interaction becomes dynamic and complicated and is still poorly understood. Here, by utilising plasmonic heating, nanolithography of polystyrene (PS) films and nanomanipulation of gold nanoparticles are realised. We find that laser power and PS film thickness as well as particle shape strongly affect the etching behaviour of the PS films, which is a synergistic effect of photothermal ablation and optical forces. Theoretical calculations and simulations rationalise the proposed mechanism, which is also verified by experimental observation. This understanding not only sheds light on how the synergistic effect of photo-ablation and optical forces acts on the particles and polymer films, but also provides a guideline for light-directed single-particle-based nanolithography and nanomanipulation.

A detailed computational model for cylindrical lithium-ion batteries under mechanical loading: From cell deformation to short-circuit onset

The safety design of systems using lithium-ion batteries (LIBs) as power sources, such as electric vehicles, cell phones, and laptops, is difficult due to the strong multiphysical coupling effects among mechanics, electrochemistry and thermal. An efficient and accurate computational model is needed to understand the safety mechanism of LIBs and thus facilitate fast safety design. In this work, a detailed mechanical model describing the mechanical deformation and predicting the short-circuit onset of commercially available 18650 cylindrical battery with a nickel cobalt aluminum oxide (NCA) system is established for the first time. The mechanical properties of anode, cathode, and separator are characterized. Based on the experiment results, the constitutive models of component materials are established and validated through numerical simulations. A detailed computational model including all components (i.e., separator, anode, cathode, winding, and battery casing) is then developed by evaluating four typical mechanical-loading conditions. Short-circuit criteria are subsequently established based on the separator failure, thereby enabling the mechanical model to predict the short circuit electrochemically. Results show that the model can describe LIB behaviors from mechanical deformation to internal short circuit. Results provide a powerful tool for the safety design of LIBs and related engineering systems.

Multidimensional Reversible Solid Oxide Fuel Cell Modeling for Embedded Applications

This paper presents a multiphysical modeling of a two-dimensional (2-D) reversible tubular solid oxide cell. The developed model can represent both a solid oxide electrolysis cell (SOEC) and solid oxide fuel cell (SOFC) operations. By taking into account of the electrochemical, fluidic, and thermal physical phenomena, the presented model can accurately describe the multiphysical effects inside a cell for both fuel cell and electrolysis cell operation under entire working range of cell current and temperature. In addition, an iterative solver is proposed which is used to solve the 2-D distribution of physical quantities along the tubular cell. The proposed model is suitable for embedded applications, such as real-time simulation or online diagnostic control. The reversible solid oxide cell model is then validated experimentally in both SOEC and SOFC configurations under different species partial pressures, operating temperatures, and current densities conditions.

Unsteady reactive magnetic radiative micropolar flow, heat and mass transfer from an inclined plate with Joule heating: A model for magnetic polymer processing

Magnetic polymer materials processing involves many multi-physical and chemical effects. Motivated by such applications, in the present work, a theoretical analysis is conducted of combined heat and mass transfer in unsteady mixed convection flow of micropolar fluid over an oscillatory inclined porous plate in a homogenous porous medium with heat source, radiation absorption and Joule dissipation. A first-order homogenous chemical reaction model is used. The transformed non-dimensional boundary value problem is solved using a perturbation method and Runge–Kutta fourth-order numerical quadrature (shooting technique). The emerging parameters dictating the transport phenomena are shown to be the gyro-viscosity micropolar material parameter, magnetic field parameter, permeability of the porous medium, Prandtl number, Schmidt number, thermal Grashof number, species Grashof number, thermal radiation–conduction parameter, heat absorption parameter, radiation absorption parameter, Eckert number, chemical reaction parameter and Eringen coupling number (vortex viscosity ratio parameter). The impact of these parameters on linear velocity, micro-rotation (angular velocity), temperature and concentration are evaluated in detail. Results for skin friction coefficient, couple stress coefficient, Nusselt number and Sherwood number are also included. Couple stress is observed to be reduced with stronger magnetic field. Verification of solutions is achieved with earlier published analytical results.

Numerical investigation of the efficiency of emission reduction and heat extraction in a sedimentary geothermal reservoir: a case study of the Daming geothermal field in China.

The utilization of geothermal energy is clean and has great potential worldwide, and it is important to utilize geothermal energy in a sustainable manner. Mathematical modeling studies of geothermal reservoirs are important as they evaluate and quantify the complex multi-physical effects in geothermal reservoirs. However, previous modeling efforts lack the study focusing on the emission reduction efficiency and the deformation at geothermal wellbores caused by geothermal water extraction/circulation. Emission efficiency is rather relevant in geothermal projects introduced in areas characterized by elevated air pollution where the utilization of geothermal energy is as an alternative to burning fossil fuels. Deformation at geothermal wellbores is also relevant as significant deformation caused by water extraction can lead to geothermal wellbore instability and can consequently decrease the effectiveness of the heat extraction process in geothermal wells. In this study, the efficiency of emission reduction and heat extraction in a sedimentary geothermal reservoir in Daming County, China, are numerically investigated based on a coupled multi-physical model. Relationships between the efficiency of emission reduction and heat extraction, deformation at geothermal well locations, and geothermal field parameters including well spacing, heat production rate, re-injection temperature, rock stiffness, and geothermal well placement patterns are analyzed. Results show that, although large heat production rates and low re-injection temperatures can lead to decreased heat production in the last 8years of heat extraction, they still improve the overall heat production capacity and emission reduction capacity. Also, the emission reduction capacity is positively correlated with the heat production capacity. Deformation at geothermal wellbore locations is alleviated by smaller well spacing, lower heat production rates, and smaller numbers of injectors in the well pattern, and by placing wells at locations with higher rock stiffness. Compared with the reference case with coal burning for heating purposes, the yearly emission reduction capacity can reach 1 × 107kg by switching to the direct utilization of geothermal energy in Daming field.

Microwave-induced electrical discharge of metal strips for the degradation of biomass tar

Considering the global energy and environment crisis, biomass energy is a major research focus. Gasification is a commonly used biomass energy conversion technology, but it inevitably yields tar as a by-product, accompanied by many hazards. This study investigates the use of microwave metal discharge as an energy-efficient alternative to current technologies for processing and treating tar from biomass gasification. The related special effects and factors affecting metal discharge were also investigated. The experimental and analytical results confirmed that microwave metal discharge could easily degrade toluene, reaching more than 50% degradation in the presence of very few (n = 5) discharge points. Compared with the traditionally employed tar-cracking process, the proposed process has distinct advantages and characteristics, particularly regarding speed and efficiency. In addition, microwave metal discharge achieves an excellent combination of multi-physical effects of light, heat, and plasma. In this study, the thermal and luminous effects associated with the discharge process were successfully studied in isolation, and a feasible mechanism research method was obtained by the appropriate test instruments and characterization parameters. This facilitates study on the mechanism of toluene degradation by microwave metal discharge. In-depth studies of the mechanism are necessary to enable the potential applications of microwave-assisted pyrolysis, pollutant removal, organic synthesis, and material preparation and regeneration.

On the paradoxical determinations of the lacuno-canalicular permeability of bone

The lacuno-canalicular permeability has been shown to play a key role in the behavior of bone tissue. The aim of this study is, by giving an overview of the determinations of this parameter, to question the paradoxical values provided by theoretical predictions and recent experimental measurements. We propose therefore a Kozeny-like law obtained by a numerical method which relates the permeability to the textural parameters of cortical bone microstructure. Moreover, we suggest possible explanations for this paradox considering the empirical difficulties and possible multiphysical effects.

The nonlinear dynamic response of microbeam of MEMS capacitive switch under mechanical shock

The microelectromechanical system (MEMS) capacitive switch based on clamped---clamped microbeam has garnered significant attention due to their geometric simplicity and broad applicability, and the accurate model which describes the multiphysical effects of MEMS capacitive switch should be developed to predict the nonlinear dynamic response of clamped---clamped microbeam. A improved macromodel of the clamped---clamped microbeam-based MEMS capacitive switch is presented to investigate the nonlinear dynamic response of clamped---clamped microbeam of MEMS capacitive switch under different mechanical shock in this article, the macromodel provides an effective and accurate design tool for this class of MEMS devices because of taking account into some effects simultaneously including midplane stretching effect, residual stress and different mechanical shock loads. A numerical analytical method based on multimode Galerkin discretization is presented to investigate the nonlinear response of clamped---clamped microbeam of MEMS capacitive switch under the different mechanical shock loads. The results show that using five or more modes can be sufficient to capture the nonlinear dynamic response of clamped---clamped microbeam, and the microbeam experiences a mechanical shock load as a quasi-static load or a dynamic load depending on the ration between the natural periods of the structure and the period or frequency of mechanical shock load. The proposed method gives the identical results to other numerical methods in the literature. Moreover, this method is straightforward to implement and could save computation efforts while not losing accuracy.

Frequency shifts in plate crystal resonators induced by electric, magnetic, or mechanical fields in surface films

We study frequency shifts in plate crystal resonators with surface films. The films are multiphysical, including the effects of inertia, stiffness, intrinsic stress, piezoelectric coupling, and piezomagnetic coupling. Mindlin's two-dimensional equations for a crystal plate with two elastic surface films are generalized to include the multiphysical effects of the films. They are used to study thickness-shear vibrations of a rotated Y-cut quartz plate with initial fields resulting from the mechanical, electric, and magnetic fields in the surface films. Frequency shifts caused by the initial fields are calculated and examined. Results show that plate crystal resonators with multiphysical surface films may be used for electric/magnetic field sensing.

Design of an Experimental Setup for Testing Multiphysical Effects on High Speed Mini Rotors

Recently, there have been numerous research projects on the development of minirotating machines. These machines mostly operate at speeds above the first critical speed and have special levitation systems. Besides, the multiphysical effects become significant in small scale. Therefore, advanced modeling approaches should be developed and innovative experimental rigs with the foregoing requirements should be constructed in order to test the developed techniques. In the current study, the design of an experimental setup for testing the multiphysical effects has been outlined. First, the previously developed multiphysical models (Dikmen, E., van der Hoogt, P., de Boer, A., and Aarts, R., 2010, “Influence of Multiphysical Effects on the Dynamics of High Speed Minirotors—Part I: Theory,” J. Vibr. Acoust., 132, p. 031010; Dikmen, E., van der Hoogt, P., de Boer, A., and Aarts, R., 2010, “Influence of Multiphysical Effects on the Dynamics of High Speed Minirotors—Part II: Results,” J. Vibr. Acoust., 132, p. 031011) for the analysis of small scale rotors are described briefly for background information. Second, an analysis of the effect of the rotor parameters (diameter, length, rotation speed, etc.) on the dynamics of the rotor under multiphysical effects is presented. Afterward the design process which includes the design decisions based on these results, the availability, simplicity, and applicability of each component is presented in detail. Finally, the experimental results have been presented and the efficiency of the design has been evaluated. In summary, the design requirements for an experimental setup for testing multiphysical effects on minirotors have been analyzed. The design procedure and evaluation of the design have been presented.

Influence of Multiphysical Effects on the Dynamics of the High Speed Mini Rotors—Part II: Results

In Part I of this work, a theoretical analysis showed that the surrounding air in the closed confinement between rotor and casing has a significant effect on the dynamic behavior of high speed minirotors. In order to validate the developed theoretical model, an experimental setup is designed and the dynamic behavior of the rotor with medium gap confinement is studied. The experimental setup has flexible supports, which consist of beams with adjustable length. The support stiffness is changed by altering the beam length. Modal analysis of the rotor is done in free-free conditions in order to test the capability of the rotordynamic model without the supports and multiphysical effects. The experimental and simulation results agree well with a difference of 1%. Then modal analysis of the whole structure is done at standstill and during operation in the absence of the casing. In this way, multiphysical effects are eliminated and only support effects on the dynamics of the structure are observed. The supports appear to have significant effect on the natural frequencies of the flexural modes of the system. Different support modeling techniques are studied and adequate equivalent models are obtained. These models are then implemented into the structural model of the rotor. Finally, multiphysical effects are tested at different speeds with different support stiffnesses. Experiments are performed with and without the casing for determining the change in the natural frequencies and onset of instability. The surrounding fluid has a significant effect on the stability of the system while the natural frequencies do not change significantly. The experimental and theoretical results are in fair agreement for predicting the natural frequencies and the onset of instability.

Influence of Multiphysical Effects on the Dynamics of High Speed Minirotors—Part I: Theory

In this study, a modeling approach has been developed to take multiphysical effects into account in the prediction of the rotordynamic behavior of high speed minirotating machinery with a moderate flow confinement. The temperature increase in the confinement and the flow induced forces resulting from the surrounding fluid have been studied and these models are combined with the structural finite element models for determining the rotordynamic behavior. The structure has been analyzed via finite elements based on Timoshenko beam theory. Flow induced forces are implemented to the structure as added mass-stiffness-damping at each node representing the structure in the fluid confinement. A thermal model based on thermal networks in steady-state has been developed. This model is used to calculate the heat dissipation resulting from air friction and temperature increase in the air gap as a function of rotation speed. At each rotation speed, the temperature in the air gap between the rotor and stationary casing is calculated and air properties, which are used for the calculation of flow induced forces are updated. In this way, thermal and fluid effects in medium gap confinements are coupled with the rotordynamic model and their effects on stability, critical speeds, and vibration response are investigated. The experimental results are reported and compared with the theoretical results in an accompanying paper (Part II).