Thermo-Viscoplastic Material Modelling for Self-heating Loads and its Experimental Verification

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

Barrier properties of GnP-PA-extruded films

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

Experimental and numerical investigation of metal-polymer riveted joints

This paper presents the modeling and analysis of the joints of metal inserts with polyamide 6 using the injection technique. Based on the experiments carried out, modeling and numerical calculations of the joints were performed for various joint configurations. The metal parts made of DS04 steel have holes. The holes are filled with polyamide 6 (PA6) by injection molding and both components are joined, resulting in a riveted joint. As part of the work, the steel / PA6 riveted joints were tested in a uniaxial tensile test. The main objective was to investigate the strength of the riveted joint as a function of the positioning and the number of rivets. A focus of the work was the numerical modeling of both the material behavior of PA6 and the riveted joint itself. The experiments showed that the polymer-metal joint with less than three rivets is destroyed by shear in the rivets. For a joint consisting of three rivets, the failure was in the rectangular polymer part. For the joint with three rivets, the maximum value of the breaking force was obtained. Similar values were obtained from numerical calculations using Abaqus software