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Composites 1

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08:35
conference time (CEST, Berlin)
FE-Based Method for Stiffness-optimized Infill Patterns for Fused Filament Fabrication with Composite Materials
26/10/2021 08:35 conference time (CEST, Berlin)
Room: J
M. König, A. Scheible, E. Vandoros, M. Lahres (Mercedes-Benz AG, DEU); P. Middendorf (University of Stuttgart, Institute of Aircraft Design, DEU)
M. König, A. Scheible, E. Vandoros, M. Lahres (Mercedes-Benz AG, DEU); P. Middendorf (University of Stuttgart, Institute of Aircraft Design, DEU)
Fused Filament Fabrication (FFF) is becoming increasingly important in the automotive industry as it enables the additive manufacturing (AM) of short fiber reinforced plastic components. AM of composites enables load bearing and highly stiff parts for the use in automotive applications (jigs, fixtures, functional prototypes). During the process, molten plastic is deposited as a continuous bead layer by layer onto a print bed until the component is completed. While adding short fibers enhances the mechanical properties of FFF parts, the anisotropic behavior increases since the fibers are aligned during printing in bead direction. This leads to high mechanical properties in bead direction, but only low strength and stiffness remain perpendicular to the bead direction. As the deposition strategy includes part orientation and infill pattern design decisions, it has a significant effect on the part’s resulting structural behavior. The objective of this work was to develop a method that enables the printing of stiffness-optimized parts via FFF with short fiber reinforced materials to increase part perfomance. The anisotropic material behavior was considered during the preparation of the part orientation and infill pattern through a structural FE analysis with an orthotropic material. An energy-based method was used to optimize the local material orientations. Afterwards, the optimized orientations were exported into a slicer programmed with Python and converted into print paths (G-code). As a result, the short fibers in the printed part are optimally aligned for a specific load case. The developed method was used to optimize infill patterns of two geometries with simple and more complex loading conditions. Afterwards, those infill patterns were compared to conventional patterns from common slicers by performing quasi-static tests. The optimized infill showed a significant increase in stiffness. The results enable engineers to prepare load path compliant infill patterns for highly stiff structural parts customized for a specific load case without additional design changes and tooling.
short fiber reinforced plastics, fused filament fabrication, infill pattern, rapid prototyping, additive manufacturing
08:55
conference time (CEST, Berlin)
A Method for Deriving a Substitution Finite Element Model of Fiber-reinforced Beaded Sheet Metals
26/10/2021 08:55 conference time (CEST, Berlin)
Room: J
P. Haberkern, A. Albers (Karlsruher Institut für Technologie (IPEK), DEU); M. Ott, W. Volk (Technical University of Munich (TUM), DEU)
P. Haberkern, A. Albers (Karlsruher Institut für Technologie (IPEK), DEU); M. Ott, W. Volk (Technical University of Munich (TUM), DEU)
Product developers often face the challenge to increase the efficiency of mechanical systems, e.g. in the automotive industry a reduction of weight results in a higher energy efficiency and less emissions. Therefore, the development of lightweight design solutions gains importance. Beads are commonly used design elements to decrease the thickness and therefore the weight of sheet metal components while maintaining the stiffness. An approach to enhance the stiffening effect of beads is the lamination of unidirectional fiber-reinforced polymers (UD-FRP) in the top flange area of the bead. However, the additional lamination of UD-FRP is expensive and adds mass to the component, which has an adverse effect on the intended weight reduction. Therefore, an optimization method is developed to determine an initial design of sheet metal components with fiber-reinforced beads. To ensure a time-efficient optimization, a substitution model of the fiber-reinforced bead structure is necessary. In this contribution, a method to derivate a substitution model of a fiber-reinforced bead is presented. As a basis, a detailed finite element model of a fiber-reinforced bead is introduced. This model is used to numerically analyze the contact and failure behavior of the combination of sheet metal and UD-FRP. The validation of the detailed model is carried out by comparing numerical results of a three-point bending test with the according experimental data. To create a substitution model of the reinforced top flange area of the detailed model, shell elements are used to replicate the behavior of the combination of sheet metal and UD-FRP. In order to achieve an equivalent behavior, the material parameter sets of these shell elements are modified. Due to the huge number of material parameters, a manual modification is too time-consuming and inefficient. Therefore, an evolutionary algorithm is implemented to generate optimized parameter sets in dependence of the utilized number of UD-FRP plies. In a further step, these sets are transferred to the optimization method to design fiber-reinforced sheet metal components. The results of the method are evaluated and presented based on the finite element models. A good accordance between the simulation results of the stress and deformation behavior of the substitution model and the detailed model can be shown. This method enables product developers to design fiber-reinforced sheet metal components.
Bead, Fiber-reinforced polymer, sheet metal, evolutionary algorithm
09:15
conference time (CEST, Berlin)
Virtual Testing of CFRP: From Unnotched Coupon to Compression After Impact Simulation
26/10/2021 09:15 conference time (CEST, Berlin)
Room: J
A. Cheruet (Hexagon, LUX); P. Martiny (Hexagon, BEL)
A. Cheruet (Hexagon, LUX); P. Martiny (Hexagon, BEL)
In the research of light weighting solutions, the use of CFRP has dramatically increased during the last two decades both in aerospace and automotive industries. However, designers are still facing the challenge to accelerate the insertion of new materials for applications. Traditionally, screening, characterization and even design of new materials is done by physical testing. However, composites materials offer an extraordinary choice of material combinations so that such traditional approaches become inefficient at best. Simulation accelerates these test campaigns, providing insights and answers well before physical coupons can be ordered, created, tested and reported. Tools, like DigimatTM propose a complete framework to conduct such simulations. This framework includes a continuum damage model to accurately capture the damage initiation and propagation that take place during the loading. Additional features are added to this model, such as cohesive elements to model the interface, in-situ strengths, mesh sensitivity control based on a crack-band method and effect of manufacturing stresses. On top of that, the platform proposes parameterized models of a large range of standard tests classically performed in the Aeronautics. This includes the classical in-plane properties (unnotched, open-hole, filled-hole, bearing and bending tests) but also the simulation of the compression after impact, where first, the damage after the impact can be predicted for a given energy level and, second, the residual strength is then computed. Finally, another aspect of the platform concerns how the analysis of the effects of defects such as out-of-ply waviness and presence of porosity on the coupon strength is addressed. The framework is applied on several coupon configurations with several aerospace composite grades.
CFRP, Virtual testing, impact, aerospace, automotive, damage
09:35
conference time (CEST, Berlin)
Simulating a Lightweighting Steering Housing Made of Reinforced Plastic
26/10/2021 09:35 conference time (CEST, Berlin)
Room: J
F. Pavia, F. Negria (Ansys Switzerland GmbH, CHE); F. Fiorini (Thyssenkrupp Presta AG, LIE)
F. Pavia, F. Negria (Ansys Switzerland GmbH, CHE); F. Fiorini (Thyssenkrupp Presta AG, LIE)
The idea of material modeling in the realm of injection-molded composites is to predict the macroscopic behavior of the material from the mechanics and physics at the microscopic level, which, in turn, are related to the details of the underlying injection process. An efficient way of predicting the microstructure's influence on the overall properties is the mean-field homogenization approach, adequate in a wide range of practical applications. Therefore, the anisotropic elasto-plastic stiffness, thermal properties, material strengths can be then directly computed as a function of the local average fiber orientation and of additional variables, such as fiber volume fraction and temperature, and can be made available for the remaining finite element simulation. Thus, in our implementation, the needed material data in the shape of a variable material response can then be transferred to other simulation environments and combined with the information on the local microstructure determined from third party simulation tools or real experimental data: this process enables us to realize accurate hierarchical multiscale and multiphysics simulations of fiber reinforced plastic components. This work discusses our approach, its benefits, and illustrates its practical and important application for the analysis of a servo-assisted automotive steering system, whose injection molded housing is made of short-fiber reinforced glass-fiber composite. In fact, since the limit of 95 g/km for CO2 emissions came into effect in the EU zone, lightweight structural design and components made of short fiber reinforced plastics started playing a central role for manufacturers of original equipment in the automotive industry. To meet such stringent requirements, a steering housing made of 50% weight glass-fiber-reinforced polyamide and manufactured through injection molding was developed at thyssenkrupp Presta AG and analyzed with the help of our new multiscale tools dedicated to short fiber composites. Multiscale modeling tools were critical in this important design and assessment phase while looking for a lighter material to be used for the housing and conferring the structure a higher (or at least the same) structural strength than that obtained with the previous metal.
short fiber composites, fiber reinforced plastics, multiscale simulations, finite element method
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