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Capillary adsorption of droplets into a funnel-like structure

Physical Review Fluids 2022年第5期7卷 054004-054004页

作者： Yanchen Wu Fei Wang Weidong Huang Michael Selzer Britta Nestler Institute for Applied Materials–Microstructure Modelling and Simulation (IAM-MMS) Karlsruhe Institute of Technology (KIT) Straße am Forum 7 Karlsruhe 76131 Germany and Institute of Digital Materials Science Karlsruhe University of Applied Sciences Moltkestraße 30 Karlsruhe 76133 Germany

Penetration of liquid with distinct volumes into a funnel-like pore structure is widely observed in nature and technical applications. However, when the droplet size is comparable with the pore size, the penetration criterion, i.e., under which condition the droplet can penetrate into the pore, remains an open question. In this work, we present theoretical models to address the penetration criteria in terms of the droplet size, the intrinsic wettability, and the opening angle of the funnel-shaped structure. The proposed theoretical models are well corroborated by phase-field simulations. Our findings demonstrate a critical contact angle below which a finite-volume droplet can penetrate into a hydrophobic pore. This critical contact angle is intimately related to the opening angle and the droplet size, which provides a complement to previous literature. Note that for a certain-sized droplet, the critical contact angle becomes invariant when the opening angle is greater than a certain threshold. Moreover, we find that for a constant opening angle, the critical contact angle decreases with the increase of the droplet size. As the droplet volume tends to be infinite, the opening angle has almost no influence on the penetration, and the critical contact angle asymptotically approaches 90∘, being consistent with previous works. Our observations illuminate a special mechanism for a precise maneuver of droplets in pore structures with potential applications in filter systems and microfluidic platforms.

关键词： Capillary interactions Coatings Contact line dynamics Drops & bubbles Flow-structure interactions Hydrophilic interactions Hydrophobic interactions Liquid bridges Surface tension effects Wetting Water

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modeling the moving boundary value problem of electrochemical machining

Modeling the moving boundary value problem of electrochemica...

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92nd Annual Meeting of the International Association of applied Mathematics and Mechanics, GAMM 2022

作者： van der Velden, Tim Ritzert, Stephan Reese, Stefanie Waimann, Johanna Institute of Applied Mechanics RWTH Aachen University Mies-van-der-Rohe-Str. 1 AachenD-52074 Germany Modeling and simulation techniques for systems of polycrystalline materials RWTH Aachen University Mies-van-der-Rohe-Str. 1 AachenD-52074 Germany

Two evolving surfaces define the moving boundary value problem in electrochemical machining. On the side of the work piece, the anodic dissolution yields the evolution of the machined surface. A novel approach for modeling the dissolution process of the anode has recently been proposed by [6], which is based on internal variables and effective material parameters that are inserted into the balance equation of electric charge. Thereby, the resulting distributions of the electric current densities-the driving forces of the dissolution process-are accurately captured without the necessity to adapt the finite element mesh in each time step. On the tool side, an efficient methodology to incorporate the movement of the cathode into the simulation without remeshing had been lacking so far. Thus, we proposed to extend the modeling approach of [6] to model the cathode also based on effective material parameters whilst using a constant finite element mesh (see [7]). The procedure allows for the consideration of arbitrarily complex geometries that additionally may possess differently oriented feed vectors. In this paper, a new anisotropic rule of mixture is put forward. The presented example is restricted to a stationary cathode, but focuses on a detailed investigation of the new methodology and a comparison with existing rules of mixture, which are a key component of the methodology and equivalently applicable to moving boundary value problems. © 2023 The Authors. Proceedings in applied Mathematics & Mechanics published by Wiley-VCH GmbH.

关键词： Cathodes

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Consideration of chemically-induced damage in a thermo-electrically coupled system

Consideration of chemically-induced damage in a thermo-elect...

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92nd Annual Meeting of the International Association of applied Mathematics and Mechanics, GAMM 2022

作者： Waimann, Johanna van der Velden, Tim Schmidt, Annika Ritzert, Stephan Reese, Stefanie Modeling and simulation techniques for systems of polycrystalline materials RWTH Aachen University Mies-van-der-Rohe-Str. 1 AachenD-52074 Germany Institute of Applied Mechanics RWTH Aachen University Mies-van-der-Rohe-Str. 1 AachenD-52074 Germany

Electro-chemical machining (ECM) allows the removal of material based on the effect of anodic dissolution and without mechanical contact. Thus, it avoids tool abrasion as well as influencing the surface quality, for instance due to formed dislocations and/or damage. Due to that, ECM is a very attractive machining process for high strength materials such as titanium. The effect of anodic dissolution is a result of a present electric current in combination with the contact with an electrolyte. We show a material model, which enables to predict the mentioned effect by use of a chemically motivated damage of the material based on Faraday’s law. After the approach’s introduction, we will address its consideration within a thermo-electrically coupled finite element method by using effective material parameters that differ between metal and electrolyte. The presentation is completed by the numerical results, which show the method’s ability to simulate the ECM process. © 2023 The Authors. Proceedings in applied Mathematics & Mechanics published by Wiley-VCH GmbH.

关键词： Electrolytes

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A Phase-Field Model for the Wetting Phenomenon of Miscible and Immmiscible Ternary Fluids

SSRN

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SSRN 2022年

作者： Wang, Fei Zhang, Haodong Wu, Yanchen Nestler, Britta Institute of Applied Materials-Microstructure Modelling and Simulation Karlsruhe Institute of Technology Straße am Forum 7 Karlsruhe76131 Germany Institute of Digital Materials Science Karlsruhe University of Applied Sciences Moltkestraße 30 Karlsruhe76133 Germany

Wetting effect has arisen great scientific interest because of its natural significance as well as technical applications. Previous models mostly focus on pure substrate fluids or binary immiscible liquid mixtures. modeling of the wetting phenomenon for multicomponent and multiphase fluids is a knotty issue. In this work, we present a phase-field model to describe the wetting effect for ternary fluids. In particular, we consider both immiscible and miscible ternary fluids, in contrast to previous immiscible ternary fluids in literature. For the miscible fluids, we vary the droplet composition and validate the present model both with Young’s law and Young-Laplace equation. For the immiscible ternary fluids, we manipulate the wettability of two contact droplets deposited on a solid substrate according to three scenarios: (I) both droplets are hydrophilic;(II) a hydrophilic droplet in contact with a hydrophobic one;(III) both droplets are hydrophobic. The contact angles at each triple junction from the simulations are compared with Young’s contact angle as well as with Neumann’s triangle rule. simulations for the validation of our work are performed in 2D and 3D. In addition, we model the evaporation process of a ternary droplet and obtain the same power law of previous experiments. Our model allows to relate the interfacial energies with surface composition, enabling to model coffee ring phenomenon in further perspective. © 2022, The Authors. All rights reserved.

关键词： Wetting

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Two-dimensional TiNBr as photocatalyst for overall water splitting

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Physical Review materials 2025年第2期9卷 025802-025802页

作者： Yatong Wang Geert Brocks Ceren Tayran Süleyman Er DIFFER – Dutch Institute for Fundamental Energy Research De Zaale 20 5612 AJ Eindhoven the Netherlands Materials Simulation and Modeling Department of Applied Physics Eindhoven University of Technology 5600 MB Eindhoven the Netherlands Computational Chemical Physics Faculty of Science and Technology and MESA+ Institute for Nanotechnology University of Twente 7500 AE Enschede the Netherlands Department of Physics Faculty of Science Gazi University Ankara 06500 Turkey

Two-dimensional (2D) Janus materials have gained increasing attention as water-splitting photocatalysts for hydrogen production. We use first-principles calculations to predict a stable 2D Janus T−TiNBr structure with strong near-ultraviolet sunlight absorption and band edges that align favorably with the water redox potentials for oxygen and hydrogen evolution. We show that the optical and electronic properties of T−TiNBr can be modulated to a certain extent by applying external uniaxial strain. Explicit calculations of the redox reactions reveal that solar-driven water splitting is viable at the N-side of T−TiNBr while the Br-side requires modifications such as vacancy creation, the application of an external potential, or adjustment of the pH conditions.

关键词： Redox reactions

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FFT-based simulation of evolving microstructures utilizing an adapting reduced set of Fourier modes

FFT-based simulation of evolving microstructures utilizing a...

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92nd Annual Meeting of the International Association of applied Mathematics and Mechanics, GAMM 2022

作者： Gierden, Christian Waimann, Johanna Svendsen, Bob Reese, Stefanie Institute of Applied Mechanics RWTH Aachen University Mies-van-der-Rohe-Straße 1 AachenD-52074 Germany Modeling and simulation techniques for systems of polycrystalline materials RWTH Aachen University Mies-van-der-Rohe-Straße 1 AachenD-52074 Germany Material Mechanics RWTH Aachen University Schinkelstraße 2 AachenD-52062 Germany Microstructure Physics and Alloy Design Max-Planck-Institut für Eisenforschung GmbH Max-Planck-Straße 1 DüsseldorfD-40237 Germany

The mechanical behavior of a periodic heterogeneous microstructure may be predicted by using a fast Fourier transform (FFT) based simulation approach. To reduce the computational effort of this method, we introduced a model order reduction (MOR) technique utilizing a reduced set of Fourier modes for the computations in Fourier space. To increase the accuracy of this MOR technique we developed a geometrically adapted sampling pattern for choosing the considered Fourier modes based on the representation of phases within the microstructure. Since the phase distribution of, for example, martensite and austenite in a polycrystalline microstructure evolves with increasing mechanical or thermal loads, the set of considered Fourier modes should also evolve according to the underlying micromechanical fields. We present the accuracy and the adaptability of this adaptive reduced set of Fourier modes by investigating the micromechanical fields of a polycrystal considering such phase transformations. © 2023 The Authors. Proceedings in applied Mathematics & Mechanics published by Wiley-VCH GmbH.

关键词： Fast Fourier transforms

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Two-scale FE-FFT-based thermo-mechanically coupled modeling of elasto-viscoplastic polycrystalline materials at finite strains

Two-scale FE-FFT-based thermo-mechanically coupled modeling ...

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92nd Annual Meeting of the International Association of applied Mathematics and Mechanics, GAMM 2022

作者： Schmidt, Annika Gierden, Christian Waimann, Johanna Svendsen, Bob Reese, Stefanie Institute of Applied Mechanics RWTH Aachen University Mies-van-der-Rohe-Straße 1 AachenD-52074 Germany Modeling and simulation techniques for systems of polycrystalline materials RWTH Aachen University Mies-van-der-Rohe-Straße 1 AachenD-52074 Germany Material Mechanics RWTH Aachen University Schinkelstraße 2 AachenD-52062 Germany Microstructure Physics and Alloy Design Max-Planck-Institut für Eisenforschung GmbH Max-Planck-Straße 1 DüsseldorfD-40237 Germany

Due to the general pursuit of technological advancement, structural components need to meet increasingly higher standards. In order to optimize the performance behavior of the used materials, detailed knowledge of the overall as well as microscopic material behavior under certain mechanical and thermal loading conditions is required. Hence, we present a two-scale finite element (FE) and fast Fourier transformation (FFT)-based method incorporating finite strains and a thermo-mechanically coupled constitutive model for elasto-viscoplastic polycrystalline materials. Assuming that the length scale of the microscale is sufficiently smaller compared to the length scale of the macroscale, we consider the macroscopic and microscopic boundary value problem as two coupled subproblems. The macroscopic boundary value problem is solved utilizing the finite element method. In each macroscopic integration point, the microscopic boundary value problem is embedded as a periodic unit cell whose solution fields are computed utilizing fast Fourier transforms and a Newton-Krylov solver. The scale transition is performed by defining the macroscopic quantities via the volume averages of their microscopic counterparts. In order to demonstrate the use of the proposed framework, we predict the macroscopic and microscopic fields of a polycrystalline material within a numerical example using an efficient and accurate FE-FFT-based two-scale method. © 2023 The Authors. Proceedings in applied Mathematics & Mechanics published by Wiley-VCH GmbH.

关键词： Polycrystalline materials

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Investigation of microstructure evolution accounting for crystal plasticity in the multiphase-field method

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PAMM 2023年第3期23卷

作者： Thea Kannenberg Lukas Schöller Andreas Prahs Daniel Schneider Britta Nestler Institute for Applied Materials—Microstructure Modelling and Simulation (IAM-MMS) Karlsruhe Institute of Technology (KIT) Karlsruhe Germany Institute of Digital Materials Science (IDM) Karlsruhe University of Applied Sciences Karlsruhe Germany Institute of Nanotechnology (INT) Karlsruhe Institute of Technology (KIT) Eggenstein-Leopoldshafen Germany

Regarding microstructured materials, a quantitative prediction of phase transformation processes is highly desirable for a wide range of applications. With respect to polycrstalline materials, the plastic material behavior is commonly investigated using a crystal plasticity (CP) theory, since it accounts for the underlying microstructure, that is, slip systems of the crystal lattice. In classical continuum mechanics, grain boundaries (GBs) are commonly modeled as material singular surfaces. However, the tracking of moving GBs, present during phase transformation processes, is numerically challenging and costly. This can be circumvented by the use of a multiphase-field method (MPFM), which provides a numerically highly efficient method for the treatment of moving interfaces, considered as diffuse interfaces of finite thickness. In this work, the microstructural evolution is investigated within the MPFM accounting for CP. The implementation of the constitutive material behavior within the diffuse interface region accounts for phase-specific plastic fields and the jump condition approach. To improve the understanding of the impact of plastic deformation on the phase evolution, a single inclusion problem is analyzed. Within a plastically deformed matrix, the shape evolution of a purely elastic inclusion with a different Young's modulus, referred to as inhomogeneity, is investigated. It is shown, how the anisotropic plastic behavior affects the phase evolution. The resulting equilibrium shapes are illustrated and examined.

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A U-Net-Based Self-Stitching Method for Generating Periodic Grain Structures

arXiv

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arXiv 2023年

作者： Ji, Ye Koeppe, Arnd Altschuh, Patrick Griem, Lars Rajagopal, Deepalaxmi Nestler, Britta Chen, Weijin Zhang, Yi Zheng, Yue Centre for Physical mechanics and Biophysics School of Physics Sun Yat-Sen University Xin’gang West Road 135 Guangdong Guangzhou510275 China Guangdong Provincial Key Laboratory of Magnetoelectric Physics and Devices School of Physics Xin’gang West Road 135 Guangdong Guangzhou510275 China State Key Laboratory of Optoelectronic Materials and Technologies School of Physics Xin’gang West Road 135 Guangdong Guangzhou510275 China Institute for Applied Materials–Microstructure Modelling and Simulation Karlsruhe Institute of Technology Strasse am Forum 7 Baden-Württemberg Karlsruhe76131 Germany Institute for Digital Materials Science Karlsruhe University of Applied Sciences Moltkestr. 30 Baden-Württemberg Karlsruhe76133 Germany

When modeling microstructures, the computational resource requirements increase rapidly as the simulation domain becomes larger. As a result, simulating a small representative fraction under periodic boundary conditions is often a necessary simplification. However, the truncated structures leave nonphysical boundaries, which are detrimental to numerical modeling. Here, we propose a self-stitching algorithm for generating periodic structures, demonstrated in a grain structure. The main idea of our algorithm is to artificially add structural information between mismatched boundary pairs, using the hierarchical spatial predictions of the U-Net. The algorithm provides an automatic and unbiased way to obtain periodic boundaries in grain structures and can be applied to porous microstructures in a similar way. Copyright © 2023, The Authors. All rights reserved.

关键词： Periodic structures

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modeling the material behavior of heterogeneous materials considering a two-scale FE–FFT-based simulation framework

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PAMM 2023年第2期23卷

作者： Annika Schmidt Christian Gierden Johanna Waimann Stefanie Reese Institute of Applied Mechanics RWTH Aachen University Aachen Germany Modeling and Simulation Techniques for Systems of Polycrystalline Materials RWTH Aachen University Aachen Germany

In various engineering applications, components subjected to high mechanical or multi-physical loads such as thermal, thermo-mechanical, or electro-thermal loads are predominantly made of metals or composites. These materials are characterized by polycrystalline or multi-phase microstructures which determine the overall material response. However, since the microscopic material behavior is directly related to the distribution, size, and morphology of the individual grains or phase constituents, precise predictions of the macroscopic material response require simulations of the microstructural behavior. Hence, this work considers a two-scale finite element (FE) and fast Fourier transform (FFT)-based simulation framework, which is an efficient alternative to the classical method for the simulation of periodic unit cells. Assuming scale separation, the macroscopic and microscopic boundary value problems are first solved individually and subsequently linked by performing a scale transition in terms of averaging the macroscopic quantities over the corresponding local fields. While the macroscopic solution is computed by means of the finite element method, the microscopic boundary value problem, which is embedded as a periodic unit cell in each macroscopic integration point, is solved using an FFT-based simulation method. In general, these microscopic simulations allow to model grain-scale phenomena such as martensitic phase transformation or plastic deformation caused by dislocation glide which can be observed in polycrystalline materials. In this work, we present a two-scale FE–FFT-based model to capture the martensitic phase transformations in shape memory alloys. In order to demonstrate the applicability of the model, a numerical example is given.

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