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Baaser H.,Freudenberg Forschungsdienste Kg | Hopmann C.,RWTH Aachen | Schobel A.,RWTH Aachen
Archive of Applied Mechanics | Year: 2013

The description of (quasi-)incompressible materials such as elastomers is well established in modern continuum mechanics for many years now as well as from a theoretical background as in the numerical implementation in commercial software packages in the context of finite elements. Nevertheless, some questions arise in the practical application of that matter describing technical components, e.g., in the discussion What are valid equivalent measures in order to compare different deformations? Here, one could request for expressions that arise in a deformation intensity and an indication of the deformation mode locally at each material point. We propose an extension of the well-known description of incompressible kinematics. We reformulate the strain invariants at incompressibility in terms of (I 1, I 2) leading to an equivalent pair (λ, m) in order to determine a distance of an arbitrary deformation state, e.g., to its equivalent shearing state. Therefore, we postulate and define an associated deformation state and give the mathematical derivation of quite nice relationships, which we demonstrate on a shear example using the finite elements method to visualize the "new" measure quantity. © 2012 The Author(s). Source

Pazur R.J.,Freudenberg Nok General Partnership FNGP | Pazur R.J.,Quality Engineering Test Establishment | Lee D.,Freudenberg Nok General Partnership FNGP | Walker F.J.,Freudenberg Nok General Partnership FNGP | Kasai M.,Freudenberg Forschungsdienste Kg
Rubber Chemistry and Technology | Year: 2012

A series of compounds based on peroxide-cured EPDM were prepared with varying amounts of paraffinic plasticizer and carbon black. Modeling of the NMR relaxation signal was successfully carried out by either a biexponential or triexponential fitting procedure. It was found the degree of plasticization correlated directly with the average molar mass between chain entanglements (M e) calculated from the short decay constant T 21. Values of M e correlated to the dynamic properties (storage modulus and tan δ) in the unvulcanized state, thus providing a measure of processability. An increase in carbon black concentration brought about a decrease in M e because of increased interactions between the filler and the polymer chain. A new parameter M chain-filler is introduced to estimate the average molar mass between polymer chains and fillers. Compared with the chain entanglement density, the overall magnitude of this interaction appears to be weak in the mobile zone of the compound matrix. As in the case of plasticization, a relatively good correlation is obtained betweenMe and the dynamical properties in the unvulcanized state. Compression-set resistance is shown to directly follow the average molar mass between cross-links (M c) before and after aging. The carbon black study results can be understood within the context of a morphological model containing different zones of chain mobility-a thin shell of immobilized chains, an intermediate zone of limited mobility, and a dominant mobile phase consisting mainly of entangled and cross-linked polymer chains. Source

Baaser H.,Freudenberg Forschungsdienste Kg | Schobel A.,RWTH Aachen | Michaeli W.,RWTH Aachen | Masberg U.,RWTH Aachen
KGK Kautschuk Gummi Kunststoffe | Year: 2011

For the efficient dimensioning of elastomer parts the structural simulation by means of Finite Element Analysis (FEA) has developed to be an indispensable tool. For the calibration of these models often only uniaxial tensile tests are conducted to estimate the material parameters. However since technical elastomer parts are usually multiaxially loaded, the accomplishment of multiaxial material testing for a precise structural simulation is essential. Different approaches for the testing of the equibiaxial tensile load condition, which can be easily converted into a pressure load condition, exist at Freudenberg Forschungsdienste (FFD) as well as at the Institute of Plastics Processing (IKV). Despite the differences at (FFD) and at the IKV in the basic principles and the mechanical set-up of both methods, comparable material answers for this load condition can be determined. Source

Losel R.,RWTH Aachen | Grafahrend D.,Freudenberg Forschungsdienste Kg | Moller M.,RWTH Aachen | Klee D.,RWTH Aachen
Macromolecular Bioscience | Year: 2010

For the reconstruction of functional tissue, biodegradable scaffolds providing specific surface functionality and a three-dimensional structure matching that of the damaged tissue are needed. Fibers capable of controlling cell-fiber interaction were produced by electrospinning of PDLLA-block-PEG with thiol-reactive end groups from a solvent mixture. The hydrophilic fibers uniquely combine minimized non-specific protein adsorption and well-defined surface reactivity allowing controlled immobilization of peptides and proteins. Human dermal fibroblasts show adherence and proliferation on the surface of RGDC-functionalized electrospun PDLLA-block-PEG fibers.Human dermal fibroblasts show adherence and proliferation on the surface of RGDC-functionalized electrospun PDLLA-block-PEG fibers. Electrospinning of PDLLA-block-PEG with thiol-reactive end groups from a suitable solvent mixture results in formation of fibers that are resistant towards protein adsorption and that can be functionalized with bioactive compounds taking advantage of their well-defined surface reactivity. Copyright © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Michaeli W.,RWTH Aachen | Hopmann C.,RWTH Aachen | Masberg U.,RWTH Aachen | Behmenburg C.,RWTH Aachen | Hoffmann M.,Freudenberg Forschungsdienste Kg
Gummi, Fasern, Kunststoffe | Year: 2011

In an ongoing research project, the Institute of Plastics Processing (IKV) at RWTH Aachen University aims to increase the energy efficiency of rubber injection moulding in cooperation with industrial partners. The demand for energy was determined in an exemplary manufacturing process. Subsequently, innovative modifications of the injection mould and the machine technology were developed and implemented. The goal is to approximate the mould entry temperature of the rubber to the crosslinking temperature and to limit the heat transfer from the mould into the environment. Source

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