Modeling,Simulation and Parameter Identification for Rate-Dependent Magnetoactive Polymer Response

A finite deformation framework for nonlinear magneto-viscoelasticity is introduced and applied to the constitutive and structural modeling of magnetoactive polymer (MAP) response. In this thermodynamically-consistent formulation the free energy function consists of purely elastic, purely magnetic and coupling contributions, where the rate-dependence is fully attributed to the non-magnetizable matrix material. The model consistently accounts for saturation in the magnetic as well as the magnetostrictive behavior. The identification of material parameters from experimental data is briefly described. Finally, a finite element model for the large strain magneto-mechanical problem is established and tested considering MAP behavior. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Simulation of a Hybrid-Forming Process using Temperature- and Rate-Dependent Viscoplastic Material Models

Hybrid-forming processes for graded structures are quite innovative methods for the production of components with tailored properties, particularly tailored material properties and geometrical shape. In this contribution a hybrid-forming process based on the utilization of locally varying thermo-mechanical effects is investigated [1]. For process optimization and improvement of the resulting work piece the simulation of the entire forming process is necessary in modern engineering. The main topics of this contribution are the simulation of the cyclic thermal loaded forming tool and the simulation of the work piece treated at large deformations with phase transformations. For both materials temperature- and rate-dependent viscoplastic material models are applied and parameter identification using cyclic tensile-compression tests for the forming tool material and phase transformation tests for a low-alloy steel similar to the work piece material is presented. For validation of finite-element-calculations for the forming tool thermal shock experiments are performed with optical deformation measurements. For validation of finite-element-calculations for the work piece numerical results of geometry and structure after heating, forming and cooling are compared to experimental micro sections. Results concerning the forming tool will be used for future lifetime prediction and results concerning the work piece will be used for future specific setting of graded material properties. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Simulation of Rate Dependent Plasticity of Polymers

Polycarbonate is an amorphous polymer which exhibits nonlinear deformation before failure. It shows a pronounced strength-differential effect between compression and tension. Strain rate influences the mechanical response of the polycarbonate. In particular, the yield stress is increased with increasing strain rate. The concept of stress mode dependent weighting function is used in the proposed model to simulate the asymmetric effects for different loading speeds. In this concept, an additive decomposition of the flow rule is assumed into a sum of weighted stress mode related quantities. The characterization of the stress modes is obtained in the octahedral plane of the deviatoric stress space in terms of the mode angle, such that stress mode dependent scalar weighting functions can be constructed. The resulting evolution equations are updated using a backward Euler scheme and the algorithmic tangent operator is derived for the finite element equilibrium iteration. The numerical implementation of the resulting set of constitutive equations is used in a finite element program for parameter identification. The proposed model is verified by showing a good agreement with the experimental data. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Modeling and Simulation of Polyoxymethylene

This essay is aimed at a brief representation of a constitutive model for a plastic called polyoxymethylene. This kind of plastic shows phenomena like tension-compression asymmetry, non-linear rate-dependence as well as a pronounced relaxation behaviour. The tension-compression asymmetry is modelled by the elastic part of the equilibrium stress state whereas the hysteretic part is described by an Armstrong&Frederick-type evolution equation. A particular viscosity function is used for describing the evolution of the viscous strains occuring in the overstress part. The model is able to represent most of the aforementioned phenomena in tension, compression and torsion experiments. In the second part of the article, the implementation of the constitutive model into the .nite element program ANSYS is described followed by a test calculation treating a nut of a bolt. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Mathematical Modeling and Simulation of Antibubble Dynamics

In this study, we propose a mathematical model and perform numerical simulations for the antibubble dynamics. An antibubble is a droplet of liquid surrounded by a thin film of a lighter liquid, which is also in a heavier surrounding fluid. The model is based on a phase-field method using a conservative Allen-Cahn equation with a space-time dependent Lagrange multiplier and a modified Navier-Stokes equation. In this model, the inner fluid, middle fluid and outer fluid locate in specific diffusive layer regions according to specific phase filed (order parameter) values. If we represent the antibubble with conventional binary or ternary phase-field models, then it is difficult to have stable thin film. However, the proposed approach can prevent nonphysical breakup of fluid film during the simulation. Various numerical tests are performed to verify the efficiency of the proposed model.     

An Approach to the Modeling of Physical Ageing in Rubbery Polymers

The oxidation reactions responsible for physical ageing are thermally activated processes and yield cross-linking similar to the vulcanization process and chain-scission reactions. Chain scission, is responsible for the relaxation behaviour under constant stretch, whereas cross-linking is responsible for hardening of the material. The decrease in the stretch at break upon cross-linking motivates the so called network alteration proposed in this contribution. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Theory and Numerics of Rate-Dependent Incremental Variational Formulations in Ferroelectricity

This paper is concerned with macroscopic continuous and discrete variational formulations for domain switching effects at small strains, which occur in ferroelectric ceramics. The developed new three–dimensional model is thermodynamically–consistent and determined by two scalar–valued functions: the energy storage function (Helmholtz free energy) and the dissipation function, which is in particular rate–dependent. The constitutive model successfully reproduces the ferroelastic and the ferroelectric hysteresis as well as the butterfly hysteresis for ferroelectric ceramics. The rate–dependent character of the dissipation function allows us also to reproduce the experimentally observed rate dependency of the above mentioned hysteresis phenomena. An important aspect is the numerical implementation of the coupled problem. The discretization of the two–field problem appears, as a consequence of the proposed incremental variational principle, in a symmetric format. The performance of the proposed methods is demonstrated by means of a benchmark problem. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Modeling and Simulation of the Portevin-Le Chatelier Effect

During deformation of an Al-Mg alloy (AA5754) dynamic strain aging occurs in a certain range of temperatures and strainrates. An extreme manifestation of this phenomenon, usually referred to as the Portevin-Le Chatelier (PLC) effect, consists in the occurrence of strain localisation bands accompanied with discontinuous yielding. The PLC effect stems from dynamic dislocation-solute interactions and results in negative strain-rate sensitivity of the flow stress. The PLC effect is detrimental to the surface quality of sheet metals and also affects the ductility of the material. Since the appearance of the effect strongly depends on the triaxiality of the stress state, three-dimensional finite element simulations are necessary in order to optimize metal forming operations. We present a geometrically nonlinear material model which reproduces the main features of the PLC effect. The material parameters were identified based on experimental data from tensile tests. Special emphasis was put on the critical strain for the onset of PLC effect, ε _c , and the statistical characteristics of the stress drop distribution. (© 2006 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.     

The Thermoregulation of Infants: Modeling and Numerical Simulation

A mathematical model is developed and used for a computer simulation of the thermoregulation of premature infants. We propose a finite volume technique for the solution of the associated partial differential equation on an unstructured grid. Emphasis is laid on the model and the validation of the numerical scheme. Beside various test runs using real life data, we present a discrete maximum principle for the steady state solution with respect to the non-convex computational domain.This revised version was published online in October 2005 with corrections to the Cover Date.     

地下矿山运输系统建模与仿真

系统仿真是系统工程领域的研究热点之一.针对大型地下矿山的运输这一庞大而复杂的系统,以云南锡业集团松树脚矿1360水平运输系统为研究对象,应用离散事件仿真原理,建立了运输系统模型.通过对某些运输参数的调整,确定了其最优的车辆分配,分析了运输系统效率,对该运输系统的运输能力做出了科学的评估.     

Modeling and Numerical Simulation of Breaking Waves on Structures

This work deals with the analytical and numerical simulation of the loads on cylindrical offshore structures due to breaking waves. We investigate breaking waves impact on a cylindrical structure on the surface of the water by using a multiphase flow model of immiscible fluids based on the Volume of Fluid (VOF) method. Different numerical schemes are applied to identify the sharp interface between water and gas. The results are compared as well with the already existing experimental, analytical and numerical studies by [1-3]. The agreement shows that the analytical and numerical models are suited to describe the experimental results. (© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

率相关晶体塑性模型的塑性各向异性分析

在Sarma和Zacharia的工作基础上,改进了单晶晶体弹粘塑性本构模型的积分算法,并采用改进的欧拉法结合迭代方法求解,特点是稳定性好计算效率较高．然后用上述模型及算法研究了:1）在单向拉伸和平面应变压缩变形下单晶塑性各向异性的特点;2）晶体模型中的主要材料参数（应变率敏感指数m和潜硬化比率q）和加载应变率对单晶塑性各向异性的影响;3）沿不同的晶体方向加载对滑移系启动的影响．     

Simulation of Electrolytes in the Modeling of Batteries

Calculating the cell voltage of a lead-acid battery requires the solution of a complex multiphysical problem including electrochemical reactions on the electrode surfaces and diffusive transport in the enclosed electrolyte. Recently, the authors proposed a new electrolyte model with a thermodynamically correct coupling of mechanics to the diffusive transport. In the analysis of that model, formal asymptotic expansions were applied to handle sharp interface layers. Here, we use this analysis to formulate a simplified model for a lead-acid battery such that it is not necessary to resolve the layers numerically, but instead there are jump conditions at double layers imposed. The cell voltage is then derived using Butler-Volmer Formula. (© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Phase Field Modeling of Crack Propagation at Large Strains with Application to Rubbery Polymers

The computational modeling of failure mechanisms in solids due to fracture based on sharp crack discontinuities exhibits drawbacks in situations with complex crack topologies. This drawback is overcome by diffusive crack modeling based on the introduction of a fracture phase field characterizing via an auxiliary variable the crack topology. In the following we extend recent advances in phase-field-type fracture based on operator split techniques, suggested in Miehe et al. [1], to the modeling of crack propagation in geometrically large deforming solids e.g. rubber-like materials. An extremely robust algorithmic treatment based on an operator split scheme is introduced consisting of three steps. Updating i) a local history-field containing the maximum reference energy, ii) the fracture phase field, and iii) the displacement field. We demonstrate the performance of proposed phase field formulation for largely deforming solids by means of a representative numerical example. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Modeling and Numerical Simulation of Cavitation for Compressible Liquid Flow

A method for the numerical simulation of cavitation phenomena based on the thermodynamic properties of liquid and steam is described. Thereby, a homogeneous cavitation model using a fully compressible discretization technique is considered. The ability of the scheme is proven by numerical experiments.     

大垂度柔索的动力学建模与仿真

用多刚体-球铰模型对大垂度柔索进行离散化建模,利用多刚体系统动力学理论建立了该模型的动力学方程.采用矩阵广义逆理论对其位移和速度进行修正,以消除该微分-代数方程在数值分析中的违约现象.数值仿真证明了该方法的正确性.