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dc.contributor.advisorKünne, B.de
dc.contributor.authorBaar, Alexander-
dc.date.accessioned2006-01-25T15:01:46Z-
dc.date.available2006-01-25T15:01:46Z-
dc.date.issued2006-01-25T15:01:46Z-
dc.identifier.isbn3-937651-04-7-
dc.identifier.urihttp://hdl.handle.net/2003/22145-
dc.identifier.urihttp://dx.doi.org/10.17877/DE290R-14187-
dc.description.abstractIn der vorliegenden Arbeit sind Dimensionierungsvorschriften zur belastungsgerechten Auslegung von Papierfaserprodukten entwickelt worden. Diese erlauben die Berechnung von mechanischen Vergleichsgrößen für räumliche Bauteile aus Papierfaserstoffen, welche im Weiteren mit den entsprechenden Versagenskennwerten verglichen werden können. Damit kann eine Abschätzung der Funktionsfähigkeit des jeweiligen Bauteils bezüglich der im Einsatzfall zu erwartenden Belastungen in frühen Phasen der Produktentwicklung erfolgen. Im Rahmen der Arbeit werden dabei zwei Versagensfälle betrachtet. Zur Dimensionierung von Faserformprodukten, die einen technischen Zweck erfüllen, wird das Versagen auf den Übergang von elastischen zu plastischen Verformungen bezogen. Zur Auslegung dieser Papierfaserprodukte wird eine berechnete Vergleichsspannung mit einer zulässigen Spannung verglichen. Das Versagen von Faserform-Verpackungen, welche die häufigsten Anwendungen für räumliche Papierfaserprodukte darstellen, wird an den plastischen Kollaps geknüpft, da diese meist nach einmaligem Gebrauch dem Recyclingkreislauf zugeführt werden. Die entwickelte Dimensionierungsvorschrift umfasst den Vergleich einer plastischen Vergleichsdehnung, welche sich aus einem elastisch-plastischen Materialmodell ergibt, mit dem plastischen Dehnungsanteil bei Probenbruch. Die Versagensgrenzwerte, die in die Dimensionierungsvorschriften einfließen, können mit Hilfe der im Rahmen der Arbeit ermittelten Regressionsmodelle in Abhängigkeit von diversen Herstellungs- und Einsatzbedingen berechnet werden. Die Modelle stützen sich dabei auf Experimentalwerte, die im Sinne der statistischen Versuchsplanung an eigengefertigten Faserformproben aufgenommen wurden. Zusammen mit der Finite Elemente Methode, die zur Ermittlung der mechanischen Vergleichsgrößen eingesetzt wird, ist es nunmehr möglich nach dem Faserformverfahren hergestellte Produkte mit ihren komplexen Bauteilgeometrien nach konstruktionsmethodischer Vorgehensweise auszulegen.de
dc.description.abstractThe pulp molding process enables the production of three-dimensional parts made of paper fibers. Thereby, the pulp is set in motion through a screen by a pressure difference. The paper fibers are filtered out of the aqueous solution and build a wet fiber mat on the screen. Further process steps involve the pressing of the wet fiber mat and the drying. Presently, molded pulp articles are primarily applied in the area of packaging products. Since only the part characteristics of finished products are measured in the packaging industry, e. g., in compression tests, and no design characteristics for the material on hand are known, the manufacturing of samples is necessary to be able to conduct product testing, which means a substantial expenditure of time and costs for molded pulp articles. On the other hand standardized testing methods of the packaging industry are not applicable for the testing of molded pulp functional parts with their variety of possible shapes differing from those of packaging products. The objective of this dissertation is the modeling of the material behavior of three-dimensional parts made of paper fibers and the determination of critical values that define the failure of the material with respect to its manufacturing parameters and operating conditions. By knowledge of those, the dimensioning of molded pulp products can be done by calculation or utilization of the finite element method in early phases of the product development. Thereby, the number of prototypes to be tested can be substantially reduced. Here, two concepts for the definition of material failure were considered: In the first case, the failure of the material is associated with the occurrence of plastic deformations and in the second, the material is said to fail, if the fiber matrix collapses. The first definition is mainly used in the methodical design of technical goods that have to maintain their shape throughout their lifecycle. This also applies for molded pulp functional parts. For molded pulp packaging parts on the other hand, which are recycled after one-time use, the occurrence of plastic deformations is said to be uncritical. For modeling purposes the previously mentioned failure criterions have to be described in terms of mathematical inequations, whereas the material is assumed to fail if an effective scalar value exceeds a critical value that is determined from uni-axial material tests. In the first case the effective stress is compared to the yield stress. The equation for the effective stress can be derived from the underlying yield criterion. To model the elastic-plastic material behavior up to the plastic collapse an associated flow-rule and an isotropic work-hardening rule were applied in addition to the yield criterion. In the region of plastic deformations the effective plastic strain is used instead of the effective stress. Due to the microscopic structure of the fiber matrix a yield stress differential between tension and compression was assumed. Uni-axial tensile and compression tests of specimen that were taken from existing packaging products confirmed this assumption. Bi-axial tensile tests were utilized to select the material model, which accounts for the yield stress differential and best predicts the material behavior under plane loading cases. The critical values for the yield stress and the plastic strain portion were determined experimentally in uni-axial tensile and compression tests, whereas the manufacturing parameters and operating conditions were varied. To account for the variation in the measured values, adaptation parameters and several safety-factors were defined. Based on these and the material model a methodical design of three-dimensional parts made of paper fibers can be conducted.en
dc.language.isode-
dc.publisherMaschinenelemente-Verlagde
dc.subjectBelastungsgerechte Auslegungde
dc.subjectDimensionierungde
dc.subjectKonstruktionde
dc.subjectGestaltungde
dc.subjectWerkstoffmodellierungde
dc.subjectPapierfaserproduktede
dc.subjectFaserformteilede
dc.subjectFasergußteilede
dc.subject.ddc620-
dc.subject.ddc670-
dc.titleModellierung der Werkstoffeigenschaften von Papierfaserprodukten als Grundlage für deren konstruktive Gestaltungde
dc.typeTextde
dc.contributor.refereeSvendsen, B.de
dc.date.accepted2005-12-16-
dc.type.publicationtypedoctoralThesis-
dc.identifier.urnurn:nbn:de:hbz:290-2003/22145-7-
dcterms.accessRightsopen access-
Appears in Collections:Fachgebiet Maschinenelemente

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