Universität Stuttgart

Now showing 1 - 4 of 4

Open Access
Weak or strong : on coupled problems in continuum mechanics
(2010) Markert, Bernd; Ehlers, Wolfgang (Prof. Dr.-Ing.)
The present work aims at giving a concise introduction to the vast field of coupled problems, particularly to those of importance in engineering and physics. Therefore, the common terminology and an appropriate classification of coupled equation systems is presented accompanied by some mathematical and computational issues. Attention is focused on volumetrically coupled multi-field formulations arising from the continuum mechanical treatment of multi-physics problems, but also geometrically coupled problems are addressed. Based on actual problems in the areas of poroelastodynamics, continuum biomechanics, and fluid-saturated porous media in general both the theoretical modeling by means of coupled continuum equations as well as the efficient numerical solution in the context of the finite element method (FEM) are presented and discussed in a problem-oriented fashion.
Open Access
Predicting fracture in disordered network materials using the local intelligent stress threshold indicator
(2025) Bachhav, Bhagyashri; Wu, Zhao; Markert, Bernd; Stamm, Benjamin; Shields, Michael D.; Falk, Michael L.; Bamer, Franz
Network glass fracture occurs as a sequence of elementary events occurring at weak sites in the glass structure. Fracture is a highly complex process that occurs suddenly and without obvious structural or thermodynamic signs prior to the event’s occurrence. We show that a stress threshold value quantified by local mechanical probing highly correlates with nanoscale crack nucleation in a two-dimensional network glass. Subsequently, a neural network-based predictor, the local intelligent stress threshold indicator (LISTI), links the local stress threshold with the undeformed local structural topology. LISTI yields a reliable heatmap indicating soft spots that strongly correlate with the localized initiation and development of the fracture process. Finally, we show that LISTI can be used to find local zones prone to rearrangement in real-measured two-dimensional silica glass structures.
Open Access
Molecular mechanics of disordered solids
(2023) Bamer, Franz; Ebrahem, Firaz; Markert, Bernd; Stamm, Benjamin
Disordered solids are ubiquitous in engineering and everyday use. Although research has made considerable progress in the last decades, our understanding of the mechanics of these materials is, at best, in an embryonic state. Since the nature of disorder complicates the realization of physically meaningful continuum-mechanical models, particle-based molecular descriptions provide a powerful alternative. This paper reviews the numerical realization of classical molecular dynamics from an engineer’s perspective, starting with selecting potential functions, boundary conditions, time integration, and thermodynamic ensembles. Then, we discuss the concept of the potential energy landscape and the computational realization of the most suitable minimization methods. Subsequently, we discuss the algorithms necessary to numerically generate disordered materials, considering their thermodynamic properties and structural identification. We comprehensively and critically review computational methods and strategies available to mimic disordered materials on a molecular level and discuss some intriguing phenomena that are, to date, mostly ignored when applying models based on continuum-mechanical frameworks. We present the crucial difference between the shear response of a crystalline and a disordered structure. In this context, we elaborate on why it is beneficial to use an overdamped, athermal description to disentangle the complex deformation mechanics of disordered solids and comprehensively discuss the theory of the mechanics of disordered materials, including the problems of prediction and reversibility. Furthermore, we examine the fracture process on the nanoscale and investigate the response behavior to more complex deformation protocols. Finally, we provide critical conclusions, including challenges and future perspectives for engineers.
Open Access
Porous media viscoelasticity with application to polymeric foams. Second revised edition
(2010) Markert, Bernd
The goal of this contribution is to merge the advances in porous media theories and the state of the art in single-phase finite viscoelasticity within a well-founded thermodynamical framework. In particular, a thermodynamically consistent constitutive setting is presented where, based on the internal variable concept, an extended Ogden-type viscoelasticity formulation is embedded into the macroscopic Theory of Porous Media (TPM). By focusing on immiscible binary solid-fluid aggregates, essential nonlinearities of the strongly coupled problem are included in the formulation. Thus, the developed biphasic continuum mechanical model accounts for the relevant physical properties stemming from the porous microstructure, the moving and interacting viscous pore fluid (compressible or incompressible), and the directly coupled intrinsic viscoelasticity of the skeleton material itself. In order to demonstrate its suitability, the presented model is especially adapted to the behavior of open-celled polymer foams, as these materials combine all nonlinearities under absolute finite viscoelastic deformations. Finally, after the numerical treatment of the governing model equations through the mixed finite element method (FEM), large strain 3-d simulations reveal the capabilities of the proposed macroscopic formulation and the efficiency of its numerical implementation.

Universität Stuttgart

Browse

Filters

Settings

Sort By

Results per page

Search Results