Modelling of thin polymer films

If we bond substrates like metal sheets by a thin polymer film we know about the existence of a boundary layer between the polymer and the substrate. The properties of this boundary layer differ from the bulk properties and influence the overall behavior of the bond. Here we present a mechanical theory based on a scalar-valued order parameter that allows us to describe these effects. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Modelling of a Cellular Rubber with Nonlinear Viscosity Functions

In this paper a porous carbon black-filled rubber is investigated under uniaxial tension. On the experimental site the main focus of attention lies on the Mullins effect, the thixotropic and the viscoelastic behaviour. Because of the two phase character of cellular rubber, the Theory of Porous Media is taken into account. Performing a proper preconditioning, the Mullins effect can be eliminated. Hence, it is not included in the material model. The constitutive model for the basic elasticity is based on a polynomial approach for an incompressible material which is expanded by a volumetric term to include the structural compressibility. Finally, the concept of finite viscoelasticity is applied introducing an intermediate configuration. Nonlinear relaxation functions are used to model the process dependent relaxation times, to simulate the thixotropy and the highly nonlinear behaviour concerning the deformation and feedrate. The material parameters of the model are estimated using a stochastic identification algorithm.     

High-resolution simulation of microstructures in dual-phase steel

Modern dual-phase (DP) steels are widely used in industry due to their favorable material behavior based on the complex microstructure. In the presented work, a microstructure based FEM model for the elasto-plastic deformation of DP steels is developed in order to accomplish a deeper understanding of the structure-property correlation. The underlying microstructure is obtained by serial section tomography. The following contribution deals with a comparison of different approaches to build a FE mesh, which is based on such microstructures. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

On the Description of Partially Saturated Soils by the Theory of Porous Media

In this contribution, a multi‐phase soil model based on the Theory of Porous Media (TPM) is presented. The model is fully coupled in the following constitutive phases: An elasto‐plastic or elasto‐viscoplastic solid skeleton, a materially incompressible pore‐liquid (water) and a materially compressible pore‐gas (air). The interaction of the solid skeleton and the pore‐fluids is specified by a capillary pressure‐saturation relation, whereas the mobilities of the fluid phases in the pore‐space of the solid skeleton are described by the so‐called relative permeabilities. Finally, a gravity governed initial‐boundary‐value problem solved by the FE method is presented.     

Characterization of short fiber reinforced polymers

This contribution presents ideas, how composite materials can be characterized with respect to experimental testing. The material properties of the investigated short glass fiber reinforced polymer are obtained by providing results from the experiment in order to seperate different material effects, such as elasticity, plasticity, damage, viscoelasticity, compressibility and anisotropy. Therefore, at first, linear uniaxial tensile tests with cyclic loadings have been realized. The application of the material in this work is the machining by a three-dimensional forming process. Hence, multiaxial loadings have to be additionally taken into account matching these conditions. In order to provide more information, biaxial tensile tests have to be realized using a testing device supplying the additional necessary experimental data [1, 2]. A final aim of this work is to develope a verification experiment representing the three-dimensional forming process as realistically as possible, e. g. a Nakajima test [4]. For this case, a three-dimensional optical analysis in order to get the necessary measurement data, is indispensable to realize an inverse method [3] by comparing the information of the complete deformation field as well as the force data of the experiment using a given material model. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)