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Author: Endres, H.-J. ×

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Now showing 1 - 10 of 26
  • Publication
    Mesh-free simulations of injection molding processes
    ( 2022)
    Veltmaat, L.
    ;
    Mehrens, F.
    ;
    Endres, H.-J.
    ;
    Kuhnert, Jörg
    ;
    Suchde, Pratik
    In this paper, we introduce a mesh-free numerical framework using the finite pointset method for the modeling and simulation of injection molding processes. When compared to well-established mesh-based methods, which have been widely applied for these applications, our approach avoids the need for extensive preprocessing and enables accurate treatment of free surfaces and other associated phenomena. To accurately model the polymer injections, we consider a detailed material model, with temperature dependent viscosity and density, while also considering shear thinning behavior with a strain rate dependent viscosity. Our numerical investigations show that injection molding-specific problems such as the modeling of viscous flows and the fountain flow effect can be successfully implemented using our presented framework. For a thorough validation of our proposed model, we compare the simulated flow behavior with injection molding experiments, which are also performed in this work. The experimental setup considers the injection of a polymer melt into a spiral mold. The flow behavior is investigated experimentally at varying melt injection and wall temperature, with different threshold pressures. Our numerical simulations show a good comparison with these experimental results, both qualitatively and quantitatively. We also introduce a correction mechanism to ensure energy conservation, which has often been challenging in mesh-free approaches. This is the first time that the flow behavior in a mesh-free injection molding method has been experimentally validated and successfully applied to the simulation of an actual industrial vehicle component.
  • Publication
    Quality analysis of downcycling processes for carbon recyclates
    ( 2018)
    Panescu, C.
    ;
    Winkelmann, J.
    ;
    Endres, H.-J.
  • Publication
    Investigation of failure mechanisms in hybrid fiber-reinforced plastics by means of in-situ-CT
    ( 2018)
    Bittner, F.
    ;
    Endres, H.-J.
    The failure mechanisms of fiber-reinforced plastics can be studied in detail with a novel In-situ-CT 4-point bending test, based on the testing standard ISO 14125. The 4-point bending test creates a complex load condition under simultaneous influence of tensile and compressive forces. By non-destructive CT measurement at different load levels the origin and development of defects can be traced. Initial tests performed on a natural and a hybrid fiber reinforced plastic reveal significant differences in defect initiation and development. Ruptures of the yarn on the tensile-loaded side characterize the failure process of the natural fiber-reinforced plastic. In the hybrid fiber-reinforced plastic carbon fibers initially show damage on the compression-loaded side followed by fiber breaks on the tensile-loaded side. Matrix failure as well as pores as potentially weak points apparently have no influence in this example. Relevant relaxation effects could be excluded on the investigated macroscopic scale.
  • Publication
    Messung der Dichteverteilung in Holzpartikelwerkstoffen in drei Dimensionen mit Computertomographie
    ( 2018)
    Plinke, B.
    ;
    Bittner, F.
    ;
    Endres, H.-J.
    Bei Holzwerkstoffen sind die Dichteverteilung in Plattenebene und das Rohdichteprofil quer dazu wichtige Maße für die Qualitätssicherung. Sie bilden jedoch nur eine oder zwei Dimensionen bei begrenzter räumlicher Auflösung ab. Computertomographische (CT-) Aufnahmen ergeben bei variabler Auflösung 3D-Daten der lokalen Absorption für Probendurchmesser von unter einem Zentimeter (z. B. Kunststoffporben mit Holzfasern) bis ca. 30 Zentimeter (Dämmstoffplatten, OSB). Unter der Annahme, dass Kernladungszahl und Absorptionskoeffizient konstant und die globale Dichte der Probe bekannt sind, ergibt ein CT-Scan bei akzeptablem Messaufwand die kalibrierte Dichteverteilung in allen drei Dimensionen und für auswählbare Teilvolumina. Daraus können deutlich mehr Informationen über den Werkstoff gewonnen werden. Zum Beispiel können die mittels Rohdichteprofilmessung nicht erfassbaren festigkeitsrelevanten horizontalen Dichtevariationen mittels CT quantifiziert wreden. Dies gilt für die "klassischen" Holzpartikelwerkstoffe, aber z. B. auch für Dämmstoffe. In höher aufgelösten CT-Scans kann auch die Partikelverteilung und -orientierung in Verbundwerkstoffen bestimmt werden.
  • Publication
    Biodegradable and bio-based green blends from carbon dioxide-derived bioplastic and poly(butylene succinate)
    ( 2017)
    Henke, L.
    ;
    Zarrinsbakhsh, N.
    ;
    Endres, H.-J.
    ;
    Misra, M.
    ;
    Mohanty, A.K.
    Conventional polymer materials from fossil fuels feature many unresolved questions regarding disposing and future resource availability. To substitute some of the established plastics with bio-based and biodegradable alternatives, new materials have to be developed and researched. The aliphatic biodegradable polyester poly(butylene succinate) offers good material properties and the perspective to be partially bio-based in the future. Poly(propylene carbonate) is an amorphous co-polymer of propylene oxide and carbon dioxide. The incorporation of carbon dioxide in the polymer offers a great way to reduce the excess CO2 levels in the atmosphere and at the same time to add a bio-based component to the plastic. By melt blending and injection molding these two materials, partially bio-based, potentially biodegradable blends are generated. The blends' mechanical, thermal and morphological properties are studied, using DSC, DMA, TMA, SEM, and FTIR analysis as well as tests regarding impact, flexural and tensile properties. Furthermore, the shrinkage of PPC, PBS and their blends is examined. It was found that blending of these two materials, without any additives or fillers, is not very promising, as almost all mechanical and thermal properties are decreased compared to the neat PBS. However, shrinkage of PPC can be eliminated when added into a PBS matrix and low contents of PPC might offer a possibility to increase the impact toughness of PBS.
  • Publication
    Filler with lightweight potential
    ( 2017)
    Uthoff, C.
    ;
    Endres, H.-J.
    ;
    Nelles, M.
    Mineral fillers are widely used in the automotive industry to enhance the performance of polymer grades. A recycling concept has now been developed, in which natural fiber-reinforced polymers are pyrolized to produce pyrolysis char as an alternative filler for thermoplastics.
  • Publication
    Polyelectrolyte treatment of cellulose fibers for the manufacture of novel bio-hybrid fiber composites (Bio-HFC) for lightweight applications
    ( 2017)
    Shamsuyeva, M.
    ;
    Endres, H.-J.
    In this study flax fabrics were treated with polyethylene imine (PEI) and afterwards, in combination with carbon fabrics, integrated into epoxy resin via vacuum infusion process. The influence of the 2 stacking sequences of the fabrics and 2 PEI concentrations were evaluated with regard to the mass fractions of the composite components and mechanical properties of the manufactured composites, namely, flexural and interlaminar shear properties. The results showed that the effect of the surface treatment is dependent on the stacking sequence. Namely, increase of the PEI concentration resulted in a corresponding increase of the mass fraction of the polymer matrix in the case of interchanging arrangement of flax and carbon fabrics. Further remarkable results showed that the same specimen provided the highest values of the supported maximum load after the surface treatment. Influence of the PEI treatment on the strength values with regard to the stacking sequence and polyelectrolyte concentration led to controversial results. Decrease of flexural modulus after the surface treatment was observed in the case of all samples.
  • Publication
    Measuring fibre orientation in sisal fibre-reinforced, injection moulded polypropylene
    ( 2017)
    Albrecht, K.
    ;
    Baur, E.
    ;
    Endres, H.-J.
    ;
    Gente, R.
    ;
    Graupner, N.
    ;
    Koch, M.
    ;
    Neudecker, M.
    ;
    Osswald, T.
    ;
    Schmidtke, P.
    ;
    Wartzack, S.
    ;
    Webelhaus, K.
    ;
    Müssig, J.
    In commercial injection moulding simulation software only tools for glass fibre-reinforced thermoplastics exist, but not for natural fibres. In our research, we adapted a simulation software for sisal fibre-reinforced polypropylene. To evaluate our simulation results, three experimental methods, to measure fibre orientation are compared to each other using injection moulded sisal fibre-reinforced polymer parts: terahertz spectroscopy, m-CT and light microscopy measurements (LMM) of microtome sections. Terahertz spectroscopy determines the main orientation over the plate thickness, but it neglects variances of fibre orientation across the plate thickness. Using m-CT and LMM allows measuring fibre orientation at different layers across the plate thickness and to detect a shell-core effect. Care has to be taken comparing results from m-CT and LMM, due to their differences in the slice thicknesses. The orientation found with the m-CT correlates well with the injection moulding simulation developed for sisal fibre-reinforced polypropylene.
  • Publication
    Dichteverteilung und Partikelstrukturen von Holzwerkstoffen
    ( 2017)
    Plinke, B.
    ;
    Bittner, F.
    ;
    Endres, H.-J.
  • Publication
    Alles hat ein Ende, nur der Kunststoff nicht
    ( 2017)
    Uthoff, C.
    ;
    Endres, H.-J.
    ;
    Nelles, M.
    Um das Eigenschaftspotential eines Kunststoffs zu verbessern, ist der Einsatz mineralischer Füllstoffe in der Automobilindustrie weit verbreitet. Pyrolysekohle bietet dazu eine interessante Alternative. Nun wurde ein Recyclingkonzept entworfen, das die Pyrolyse von naturfaserverstärkten Kunststoffen zur Produktion von Pyrolysekohle als Füllstoff in Thermoplasten umfasst.