Well-Posedness of Mathematical Models in Continuum Mechanics and Thermodynamics

In the paper, the coupling between the well-posedness of models for the continuum mechanics and thermodynamics is studied.     

Polycrystal vs. Classical Continuum Models for Structures

In this work a comparison of polycrystal and classical continuum models illustrated by examples of full structures is investigated. The general idea is to represent the averaged distribution of displacement, stress and strain fields for statistically randomized realizations of discrete structures. A technique for averaging fields in the FEM program ABAQUS is proposed and implemented. To improve the computation efficiency mesh dependence was investigated. Results of simulation are given for a rectangular plate and for the Kirsch's problem for both examples elastic as well as inelastic material behavior. (© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Higher-Order Anisotropic Caginalp Phase-Field Systems

Our aim in this paper was to study the well-posedness and the dissipativity of higher-order anisotropic phase-field systems. More precisely, we prove the existence and uniqueness of solutions and the existence of the global attractor.

     

Phase-Field Modeling of Hydraulic Fracture

Hydraulically driven fracture has gained more and more research activity in the last few years, especially due to the growing interest of the petroleum industry. Key challenge for a powerful simulation of this scenario is an effective modeling and numerical implementation of the behavior of the solid skeleton and the fluid phase, the mechanical coupling between the two phases as well as the incorporation of the fracture process. Existing models for hydraulic fracturing can be found for example in [1], where the crack path is predetermined, or in [2] who use a phase field fracture model in an elastic framework, however without incorporating the fluid flow. In this work we propose a new compact model structure for the Biot-type fluid transport in porous media at finite strains based on only two constitutive functions, that is the free energy function ψ and a dissipation potential ϕ that includes the incorporation of an additional Poiseuille-type fluid flow in cracks. This formulation is coupled to a phase field approach for fracture and is fully variational in nature, as shown in [3]. In contrast to formulations with a sharp-crack discontinuity, the proposed regularized approach has the main advantage of a straight-forward modeling of complex crack patterns including branching. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Phase-Field Modeling and Numerical Simulation for Ice Melting

In this paper, we propose a mathematical model and present numerical simulations for ice melting phenomena. The model is based on the phase-field modeling for the crystal growth. To model ice melting, we ignore anisotropy in the crystal growth model and introduce a new melting term. The numerical solution algorithm is a hybrid method which uses both the analytic and numerical solutions. We perform various computational experiments. The computational results confirm the accuracy and efficiency of the proposed method for ice melting.     

A Quasi-Stationary Phase-Field Model with Micro-Movements

This note addresses the global strong solvability of a phase-field system arising in connection with the phase transition theory recently proposed by Frémond. The novelty of this modelization consists in considering the macroscopic effect of the microscopic movements of particles of the system that undergoes the phase transition. In particular, we outline the basic features of this model and deal with the upcoming nonlinear PDE system in the one-dimensional setting by means of an approximation—a priori estimates—passage to the limit procedure.     

Infinitesimals and the Continuum

The Mathematical Intelligencer -     

Revisit of Semi-Implicit Schemes for Phase-Field Equations

It is a very common practice to use semi-implicit schemes in various computations, which treat selected linear terms implicitly and the nonlinear terms explicitly. For phase-field equations, the principal elliptic operator is treated implicitly to reduce the associated stability constraints while the nonlinear terms are still treated explicitly to avoid the expensive process of solving nonlinear equations at each time step. However, very few recent numerical analysis is relevant to semi-implicit schemes, while "stabilized" schemes have become very popular. In this work, we will consider semi-implicit schemes for the Allen-Cahn equation with $general$ $potential$ function. It will be demonstrated that the maximum principle is valid and the energy stability also holds for the numerical solutions. This paper extends the result of Tang & Yang (J. Comput. Math., 34(5) (2016), pp. 471-481), which studies the semi-implicit scheme for the Allen-Cahn equation with $polynomial$ $potentials$.     

Phase-Field Modeling of Fracture in Anisotropic Media

In the recent years phase-field modeling of fracture has become a promising tool to describe complex crack patterns in all kinds of solid materials. Many of the models assume an isotropic material behavior, which of course is not a meaningful assumption for e.g. biological tissues such as arterial walls. Since the phase-field approach introduces an additional (smeared) phase describing the evolution of the crack, this method is well suited to be extended to anisotropic materials without thinking about an adaption of the discretization technique. Anisotropy can be incorporated in several ways, like by an extension of the surface energy, i.e. by making the energy release rate orientation dependent, as considered in [1]. Our ansatz is based on a pure geometrical approach, namely on an anisotropic formulation of the crack surface itself. Here, we will focus on transversely isotropic and cubically anisotropic solids, where the latter one makes the incorporation of the second gradient of the crack phase field necessary. At the end one numerical example is shown, which conceptually shows the influence of the anisotropy on the crack path. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

一个完全双曲相场系统的指数吸引子

本文研究一个非线性双曲微分积分系统,它由H.G.Rotstein等人于2001年提出,用来描述某种特殊的相位转换现象.该系统刻画了相对温度(?)和序参数(或相场)x的变化规律.对(?)和x分别赋予Dirichlet和Neumann边界条件下,该问题生成一个耗散的动力系统,Grasselli和Pata证明了该系统整体吸引子的存在性,随后,Grasselli证明了该系统的指数吸引集的存在性.本文进一步证明其指数吸引子的存在性,在得到指数吸引子有有限的分形维数的同时得到整体吸引子的分形维数的有限性.     

Direct and Inverse Problems for a Phase-Field Model with Memory

We consider a semilinear integrodifferential system in non-normal form. Such a system is a generalization of the one that arises in the phase-field theory with memory. We prove an abstract existence and uniqueness theorem and a continuous dependence result for the direct problem. Reformulating the direct problem in a suitable way we prove that the identification problem admits a unique solution.     

A Magneto-Mechanically Coupled Phase-Field Model at Large Deformation

The aggregate magneto-mechanical behavior of magneto-rheological elastomers (MREs) stems from the magnetic properties of the ferromagnetic inclusion and the mechanical properties of the matrix material. We propose a large deformation micro-magnetic theory, to predict the behavior and interaction of ferromagnetic particles inside an elastomeric matrix. A rate-type variational principle, with the magnetization as the order parameter is proposed. A large deformation Landau-Lifshitz-Gilbert equation for the time evolution of the magnetization, is obtained directly from the proposed variational principle. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

模糊集的基数与连续统假设

本文在模糊映射的基础上给出了模糊集基数的定义，它把普通集的基数作为特款；不但得到有关基数的大部分结论，而且有其自身的特殊性质；特别，对于连续统假设这一世界难题可能有新的启示．     

连续统与Turing度

令Ｄ为所有Ｔｕｒｉｎｇ度的集合，≤为Ｄ上的图林化归关系．一函数ｆ：Ｄ→Ｄ称为前进函数如果对任何ａ∈Ｄ，ａ≤ｆ（ａ）。对于一个前进函数ｆ，我们说Ｄ中的两个度ａ，ｂ是ｆ－不可比较的，如果ａ≮ｆ（ｂ）且ｂ ≮ｆ（ａ），否则是ｆ－可比较的．本文的一个主要结果是：在ＺＦＣ中连续统假设成立当且仅当存在一个前进函数ｆ：Ｄ→Ｄ使得Ｄ中任何两个度都是ｆ－可比较的.     

Asymptotic Compactness and Attractors for Phase-Field Equations in ℝ3

In this paper we study the asymptotic behaviour of solutions of the phase-field system on an unbounded domain. We do not assume conditions on the non-linear term ensuring the uniqueness of the Cauchy problem, so that we have to work with multivalued semiflows rather than with semigroups of operators. In this way we prove the existence of a global attractor by considering the convergence in an appropriate weighted space. This result is also new for more restrictive conditions, which guarantee the uniqueness of solutions.     

微极连续体力学比经典连续体力学更深入一层次

本文通过刚删架(动静态响应与屈曲)的微极梁板模型,血液的牛顿-微极分层流模型以及人骨微极特性的实验论证等阐明微极连续体理论的本质特点,从应用侧面阐述微极连续体力学比经典连续体力学更深一层次的观点,并介绍该理论及其近期应用的部分进展情况。     

A Phase-Field Model Based on a Three-Phase-Lag Heat Conduction

Our aim in this article is to study a phase-field system based on a three-phase-lag for the thermal flux vector. In particular, we prove the existence and uniqueness of solutions and then study the spatial behavior of the solutions in a semi-infinite cylinder, when such solutions exist.     

A Phase-Field Model of Ductile Fracture at Finite Strains

This work outlines a variational-based framework for the phase field modeling of ductile fracture in elastic-plastic solids at large strains. The phase field approach regularizes sharp crack discontinuities within a pure continuum setting by a specific gradient damage model with geometric features rooted in fracture mechanics. Based on the recent works [1, 2], the phase field model of ductile fracture is linked to a formulation of gradient plasticity at finite strains in order to ensure the crack to evolve inside the plastic zones. The thermodynamic formulation is based on the definition of a constitutive work density function including the stored elastic energy and the dissipated work due to plasticity and fracture. The proposed canonical theory is shown to be governed by a rate-type minimization principle, which determines the coupled multi-field evolution problem. Another aspect is the regularization towards a micromorphic gradient plasticity-damage setting which enhances the robustness of the finite element formulation. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)