Auslegung und Konstruktion eines Harvesterkopfs in Leichtbauweise

Translated title of the contribution: Lightweight design and construction of a harvester head

Fritz Oppliger

Research output: ThesisDiploma Thesis

Abstract

The demands of the forest industry for lightweight design and subsequent weight savings have to consider the strength limitations of the materials, the manufacturing process and the available design space for the investigated components. An important precondition for optimal light-weight design is the know-how of realistic load assumptions both for the design stage and the fatigue assessment. This work deals with the light-weight design of the wood harvester head “Woody 60”. Starting with load-measurements, load spectra for the delimbing knife, drive rollers and the frame structure are derived and used as input for the numerical simulation and the structural optimization which allows the systematic development of lightweight components. The application of the strain gauges and the subsequent measurement of local strains were performed on positions with excessive local stress concentration. To provide a comparison with the real operating conditions the local stresses have been measured over a specified working period. In the respective time intervals different load cases were acting onto the components, by working at the felling or the delimbing process in different wood qualities and trunk diameters. The maximum load occurs during the delimbing process, wherein the tree is moved horizontally by hydraulic driven feed rollers. During this operating condition, the branches are shared off by the variable delimbing knifes. The result of experimental measurement of local stresses is a load spectrum which is used for the numerical calculation. To evaluate the forces on the components, a simplified equivalent model is applied and calculated by using the finite element method (FEM). One of the numerical results was the stress and strain distribution of the entire delimbing knife which serves as basis for the topology optimization. The aim of the optimization is to maximize the stiffness of the component by minimization of the weight. Furthermore, a lightweight prototype of the roller unit and the frame structure of the harvester head were constructed. The application of topology optimization and the selection of high-strength materials and application of a corresponding manufacturing concept offered a significant reduction in weight by 12 % and fulfils the expected demands in light-weight design.
Translated title of the contributionLightweight design and construction of a harvester head
Original languageGerman
QualificationDipl.-Ing.
Supervisors/Advisors
  • Grün, Florian, Supervisor (internal)
  • Leitner, Martin, Co-Supervisor (internal)
  • Fössl, Thomas, Co-Supervisor (external)
Award date14 Dec 2012
Publication statusPublished - 2012

Bibliographical note

embargoed until 17-10-2017

Keywords

  • lightweight
  • structural optimization
  • strain gauges
  • topology optimization

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