Maik Gude

Experimental comparison of a macroscopic draping simulation for dry non-crimp fabric preforming on a complex geometry by means of optical measurement

Scope of the presented work is a detailed comparison of a macroscopic draping model with real fibre architecture on a complex non-crimp-fabric preform using a new robot-based optical measurement system. By means of a preliminary analytical process design approach, a preforming test centre is set up to manufacture dry non-crimp-fabric preforms. A variable blank holder setup is used to investigate the effect of different process parameters on the fibre architecture. The real fibre architecture of those preforms is captured by the optical measurement system, which generates a three-dimensional model containing information about the fibre orientation along the entire surface of the preform. The measured and calculated fiber orientations are then compared with the simulation results in a three-dimensional overlay file. The results show that the analytical approach is able to predict local hot spots with high shear angles on the preform. Macroscopic simulations show a higher sensitivity towards changes in blank holder pressure than reality and limit the approach to precisely predict fibre architecture parameters on complex geometries.

Multi-scale structuring for thermoplastic-metal contour joints of hollow profiles

In contrast to common and classical joining technologies for composite/metal hybrid structures such as bonding and riveting, profile and contour joints offer a promising potential for novel lightweight hybrid structures. Contour joints with form locking elements on multiple scale levels enable to pass very high loads into rod- and tube-shaped fibre reinforced structures and promise high degrees of material utilization for the composite part. This paper demonstrates the advantage of multi-scale structured load introduction elements. First the intrinsic manufacturing process, whereas the thermoplastic tape braided preform is simultaneously consolidated and formed into the metallic load introduction element is shown. Numerical investigations on the macro- and generic microscale demonstrate the potential to trigger cohesive or adhesive failure by appropriate designed form locking elements. The extensive experimental investigation of meso-, macro- or combined-structured tubular specimen shows the beneficial effect of multi-scale structuring to increase the joining strength. Concluding advises for the contour joints’ design are given.

Experimental and numerical studies on the braiding of carbon fibres over structured end-fittings for the design and manufacture of high performance hybrid shafts

Braiding is an attractive manufacturing method for tubular elements such as hollow shafts and struts. One of the main challenges however is the integration of suitably performing end-fittings. Recent advances in additive layer manufacture have enabled the fabrication of end-fittings which can be ‘co-impregnated’ or ‘co-cured’ with the fibre preform in a single step, i.e. without the need for secondary adhesive bonding. This requires the introduction of protrusions onto the surface of the end-fitting to promote mechanical interlocking with the fibres. However, the lack of accurate modelling tools for the simulation of this manufacturing process means that much empiricism is currently used in the design of such structures.xa0A novel numerical framework is presented here for the full-scale simulation of the braiding process over structured end-fittings. Nonlinear finite element analysis is applied at the meso-scale, with strands of beam elements representing individual yarns and meshed surfaces modelling the mandrel and tooling. Penalty-based contact formulations are then used to simulate all inter-yarn and yarn-metal interactions, enabling detailed predictions of fibre paths around surface protrusions. In order to verify and validate this numerical framework, a series of full-scale braiding experiments was conducted using additively-manufactured thermoplastic mandrels. Final braid patterns as well as the occurrence of braid imperfections were investigated and compared to model predictions. It is shown that the proposed modelling strategy reproduces well the trends observed experimentally in terms of final braid quality. A parametric study was then conducted on the effects of initial end-fitting alignment with respect to oncoming yarns, suggesting that better control over this parameter could reduce considerably the occurrence of braid imperfections.

Correlation between elastic and plastic deformations of partially cured epoxy networks

The thermo-mechanical behavior of polymer matrix materials is strongly dependent on the curing reaction as well as temperature and time. To date, investigations of epoxy resins and their composites mainly focused on the elastic domain because plastic deformation of cross-linked polymer networks was considered as irrelevant or not feasible. This paper presents a novel approach which combines both elastic and plastic domain. Based on an analytical framework describing the storage modulus, analogous parameter combinations are defined in order to reduce complexity when variations in temperature, strain rate and degree of cure are encountered.The thermo-mechanical behavior of polymer matrix materials is strongly dependent on the curing reaction as well as temperature and time. To date, investigations of epoxy resins and their composites mainly focused on the elastic domain because plastic deformation of cross-linked polymer networks was considered as irrelevant or not feasible. This paper presents a novel approach which combines both elastic and plastic domain. Based on an analytical framework describing the storage modulus, analogous parameter combinations are defined in order to reduce complexity when variations in temperature, strain rate and degree of cure are encountered.

Characterising the thermoforming behaviour of glass fibre textile reinforced thermoplastic composite materials

Textile reinforced thermoplastic composites are predestined for highly automated medium- and high-volume production processes. The presented work focusses on experimental studies of different types of glass fibre reinforced polypropylene (GF-PP) semi-finished thermoplastic textiles to characterise the forming behaviour. The main deformation modes fabric shear, tension, thought-thickness compression and bending are investigated with special emphasis on the impact of the textile structure, the deformation temperature and rate dependency. The understanding of the fundamental forming behaviour is required to allow FEM based assessment and improvement of thermoforming process chains.Textile reinforced thermoplastic composites are predestined for highly automated medium- and high-volume production processes. The presented work focusses on experimental studies of different types of glass fibre reinforced polypropylene (GF-PP) semi-finished thermoplastic textiles to characterise the forming behaviour. The main deformation modes fabric shear, tension, thought-thickness compression and bending are investigated with special emphasis on the impact of the textile structure, the deformation temperature and rate dependency. The understanding of the fundamental forming behaviour is required to allow FEM based assessment and improvement of thermoforming process chains.

Studie zum ressourceneffizienten Leichtbau

Ganzheitlicher Ansatz Angestoßen durch die Nationale Plattform Elektromobilität (NPE) widmet sich das Forschungsund Technologiezentrum für ressourceneffiziente Leichtbaustrukturen der Elektromobilität (Forel) seit 2013 der systemisch koordinierten Weiterentwicklung des Leichtbaus für den Einsatz in Fahrzeugen der Zukunft. Ziel ist die Entwicklung neuer Bauweisen, Technologien und Prozesse sowie die Schaffung direkter Transferund Verwertungsmöglichkeiten der Forschungsergebnisse in industrielle Wertschöpfungsketten. Auf bauend auf den Erkenntnissen der Forel-Studie 2015 [1] sowie den Forschungsund Entwicklungsergebnissen von nunmehr zehn Forel-Technologieprojekten wird in der aktuellen Studie der derzeitige Technologiewandel in der Mobilität untersucht [2]. Dazu wurden eine Onlineumfrage Autoren

Calculation method for the determination of stress concentrations in fibre-reinforced multilayered composites due to metallic interference-fit bolt:

Sophisticated analytical solution methods for the stress concentration problem in multilayered composites with interference-fit bolts have been developed on the basis of layer-related solutions. The model is based on a circular or elliptical isotropic bolt integrated in a fibre- or textile-reinforced multilayered composite plate. For the simulation of the interference between bolt and composite plate a modelling strategy has been proposed featuring the application of a defined temperature load to a metallic elastic inclusion. For analysing the stress concentration effects in the surrounding plate, complex-valued displacement functions in combination with the method of conformal mappings for the interface between inclusion and plate and a combination of boundary collocation and least squares method for the outer boundary are used. For the verification of the developed calculation methods, a number of experimental and numerical studies have been carried out and the decay behaviour of the distortions have been compared for different radians. For all combinations of multilayered composite plate and interference-fit bolt investigated so far, a good correlation of the analytically calculated and the numerically determined results can be observed.