TY - GEN A1 - Sparr, Holger A1 - Roszak, Robert A1 - Sagradov, Ilja A1 - Schob, Daniela A1 - Ziegenhorn, Matthias T1 - Thermo-viscoplastic material modelling for self-heating loads and its experimental verification T2 - Technische Mechanik N2 - The paper examines a modelling approach for thermomechanically coupled problems and an experimental concept for a material law validation and verification for self-heating with small to moderate temperature ranges. The study compares two different model formulations and is generally applicable to a variety of material classes. One model is based on a rheological network with an extension for dissipative deformation below the elastic limit. The other model operates without a yield condition. Both models are applied to published experimental data in terms of rate-independent behaviour and the evaluation is carried out on stress-strain-level, temperature evolution and the energy transformation ratio. Furthermore the two models are applied to a strain rate-dependent load case conducted at our institute discussing the same entities. It is pointed out, that the approach of a thermomechanical analysis is valuable and informative to assess the observed deformation processes and to describe the material behaviour with a thermodynamically valid parameter set. KW - Thermomechanics KW - self–heating KW - viscoplasticity KW - energy transformation ratio KW - thermography Y1 - 2020 U6 - https://doi.org/10.24352/UB.OVGU-2020-015 SN - 2199-9244 SN - 0232-3869 VL - 40 IS - 1 SP - 66 EP - 76 ER - TY - GEN A1 - Schob, Daniela A1 - Sagradov, Ilja A1 - Roszak, Robert A1 - Sparr, Holger A1 - Franke, Rainer A1 - Ziegenhorn, Matthias A1 - Kupsch, Andreas A1 - Leonard, Fabien A1 - Müller, Bernd R. A1 - Bruno, Giovanni T1 - Experimental determination and numerical simulation of material and damage behaviour of 3d printed polyamide 12 under cyclic loading T2 - Engineering Fracture Mechanics N2 - The material and damage behaviour of additively manufactured polyamide 12 under cyclic loading was characterized by cyclic tests and microstructure analysis by using microscopy, X-ray refraction, and computed tomography. The results were used to determine parameters for the viscoplastic material model by Chaboche and a damage model by Gurson-Tvergaard-Needleman. The temperature was monitored during the experiments and the self-heating effect was observed. By including this effect, a higher accuracy could be achieved with the results of mechanical experiments. KW - 3D printing Polyamide 12 KW - Chaboche model KW - GTN model KW - Material and damage behaviour KW - X-ray refraction KW - computed tomography Y1 - 2020 U6 - https://doi.org/10.1016/j.engfracmech.2019.106841 SN - 0013-7944 VL - 229 ER - TY - GEN A1 - Boldt, Regine A1 - Leuteritz, Andreas A1 - Schob, Daniela A1 - Ziegenhorn, Matthias A1 - Wagenknecht, Udo T1 - Barrier Properties of GnP–PA-Extruded Films T2 - Polymers N2 - It is generally known that significant improvements in the properties of nanocomposites can be achieved with graphene types currently commercially available. However, so far this is only possible on a laboratory scale. Thus, the aim of this study was to transfer results from laboratory scale experiments to industrial processes. Therefore, nanocomposites based on polyamide (PA) and graphene nanoplatelets (GnP) were prepared in order to produce membranes with improved gas barrier properties, which are characterized by reduced permeation rates of helium. First, nanocomposites were prepared with different amounts of commercial availably graphene nanoplatelets using a semi-industrial-scale compounder. Subsequently, films were produced by compression molding at different temperatures, as well as by flat film extrusion. The extruded films were annealed at different temperatures and durations. In order to investigate the effect of thermal treatment on barrier properties in correlation to thermal, structural, and morphological properties, the films were characterized by differential scanning calorimetry (DSC), wide angle X-ray scattering (WAXS), optical microscopy (OM), transmission electron microscopy (TEM), melt rheology measurements, and permeation measurements. In addition to structural characterization, mechanical properties were investigated. The results demonstrate that the permeation rate is strongly influenced by the processing conditions and the filler content. If the filler content is increased, the permeation rate is reduced. The annealing process can further enhance this effect. KW - graphene nanoplatelets KW - polyamide KW - nanocomposites KW - flat film extrusion KW - permeation rate Y1 - 2020 U6 - https://doi.org/10.3390/polym12030669 SN - 2073-4360 VL - 12 IS - 3 ER - TY - GEN A1 - Sagradov, Ilja A1 - Schob, Daniela A1 - Roszak, Robert A1 - Maasch, Philipp A1 - Sparr, Holger A1 - Ziegenhorn, Matthias T1 - Experimental investigation and numerical modelling of 3D printed polyamide 12 with viscoplasticity and a crack model at different strain rates T2 - Materials Today Communications N2 - This contribution presents an investigation of strain rate dependent behaviour for selective laser sintered polyamide 12. Two different cases are considered: a strain rate change within tensile loading and a relaxation test incorporating a strain rate change after each holding time section. For the simulation of material behaviour the material model of Bodner-Partom and Chaboche were used. The damage behaviour was considered by the Lemaitre crack model. Thereby it was determined which numerical model is more suitable to reproduce the strain rate-dependent behaviour. Tensile and relaxation tests at constant speeds served as the basis for these investigations. KW - SLS-PA12 KW - Rate-dependent Chaboche model KW - Bodner-Partom model KW - Lemaitre Y1 - 2020 UR - https://www.sciencedirect.com/science/article/abs/pii/S2352492820325538 U6 - https://doi.org/10.1016/j.mtcomm.2020.101542 SN - 2352-4928 VL - 25 ER -