Anwendung des lokalen Spannungskonzeptes zur Lebensdauerberechnung von kurzglasfaserverstärkten Spritzgusskomponenten

Translated title of the contribution: Application of the local stress concept for lifetime analysis of injection moulded short glass fibre reinforced components

Philip Pichler

Research output: ThesisDiploma Thesis

Abstract

Short glass fibre reinforced (sgfr) plastics are found in a broad range of applications nowadays. Especially structural metallic components are often replaced because of the high specific strength of sgfr plastics in reference to lightweight design. Furthermore, the injection moulding process offers the opportunity to produce components highly cost-efficient in large amounts. Because of the meltflow caused by the production process the orientation of the fibres are different, which leads to anisotropic properties. The primary goal of this thesis is the lifetime analysis of a structural validation part and to compare the results with a component test. Therefore, required material specifications, which are partly used in the fatigue durability software FEMFAT, are investigated with quasistatic and cyclic tests. The considered material is a thermoplastic polyetherimide with 30 wt% milled glass fibres. On the basis of standardised test specimens as well as short specimens taken from a plate in orthogonal direction, influences like weldline, fibre orientation and high temperatures are investigated. The weldline reduces the fatigue strength by 48 %. Short specimens taken transversal to main fibre orientation are showing a 20 % lower dynamic stress limit than longitudinal extracted ones. Furthermore, the influence of high temperatures (T = 120 °C) decreases the fatigue strength, depending on the main fibre orientation, up to 37 %. Failure analysis showed that fibres are mainly pulled out of the matrix, this means that the adhesion between fibre and matrix is quite low. Moreover, the water absorption of the material was investigated. The storage of standardised specimens in indoor climate and water with 50 °C has shown absorption of water up to 0.7 %. For testing the structural part, which is a lens holder of a car headlight, a test device was designed and produced. The measured load cycles on a servohydraulic test rig under different loadcases are the reference for the validation of the lifetime calculation in FEMFAT. For lifetime analysis two different material datasets are used (isotropic and anisotropic to consider the local fibre orientations). The comparison between simulation and test showed good but conservative results. Depending on the used material dataset and the applied loadcase, safety factors between 1.2 and 2 are calculated, in reference to the stress. This means that the component under cyclic loading in the reality is more resistant than virtually calculated. It is shown that the results with the anisotropic material dataset are more precise than the isotropic.
Translated title of the contributionApplication of the local stress concept for lifetime analysis of injection moulded short glass fibre reinforced components
Original languageGerman
QualificationDipl.-Ing.
Supervisors/Advisors
  • Grün, Florian, Supervisor (internal)
Award date13 Dec 2013
Publication statusPublished - 2013

Bibliographical note

embargoed until 11-11-2015

Keywords

  • lifetime analysis
  • fatigue life calculation
  • validation
  • weldline
  • temperature
  • fibre orientation
  • moisture
  • component test
  • short glass fibre reinforced
  • FEMFAT
  • polyetherimide
  • PEI
  • GX30
  • fatigue

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