Ansätze zur spannungsbasierenden und bruchmechanischen Charakterisierung des Ermüdungsverhaltens von glasfaserverstärktem Polyamid

Translated title of the contribution: Stress based and fracture mechanics approaches to characterize the fatigue behavior of glass fiber reinforced polyamide

Andreas Mösenbacher

Research output: ThesisDiploma Thesis

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Abstract

The aim of this thesis is the determination of fatigue data based on the traditional Wöhler fatigue test and the fatigue crack propagation test, on a 50 wt-% short glass fibre reinforced Polyphtalamid (PPA). To compete in the daily competition, it is increasingly important to reduce development time and costs. Based on correlation analyses between the stress based and fracture mechanics fatigue approach, the transferibility of fatigue data from fatigue crack propagation tests to the S/N-curve, is evaluated. Also, a method is developed for analog measurement of crack length by crack-gages. For dimensioning cyclically loaded components of short glass fibre reinforced plastics, the knowledge of fatigue data and fatigue affecting parameters is necessary. The effects of notches and elevated ambient temperature (120 °C) are investigated by S/N-curves. Stress data, which are necessary to describe the supporting effect behaviour (stress concentration factor Kt, and relative stress gradient ), are investigated by a finite-element-simulation. The fracture mechanical characterisation of the material includes fracture toughness tests and fatigue crack propagation tests. The test specimens for these tests (compact-type (CT)-specimen) are milled from injection-moulded plates. The effect of fibre main orientation and ambient temperature on the fracture mechanical behaviour is analyzed. In the studies concerning the correlation of stress based and fracture mechanics fatigue approach, both the long life fatigue range and the fatigue range are considered. Two different types of initial crack configurations are selected using the linear-elastic fracture mechanics approach for the conversion from fracture mechanics to the stress based results. Based on the definded assumptions the investigated material shows a very good correlation. It is shown, that a first approximation of the S/N-curve by time sparing fracture mechanics fatigue crack propagation tests is possible. Especially for the specification of trends in the fatigue behaviour, as a result of elevated temperature, the fracture mechanics fatigue approach is very well suited. However, the fracture mechanics fatigue approach is no full replacement for traditional S/N-curve investigations.
Translated title of the contributionStress based and fracture mechanics approaches to characterize the fatigue behavior of glass fiber reinforced polyamide
Original languageGerman
QualificationDipl.-Ing.
Supervisors/Advisors
  • Guster, Christoph, Co-Supervisor (internal)
  • Eichlseder, Wilfried, Supervisor (internal)
Award date18 Dec 2009
Publication statusPublished - 2009

Bibliographical note

embargoed until null

Keywords

  • short glassfiber reinforced polyamid S/N-curve linear elastic fracture mechanics correlation of S/N-curve and crack growth curve fatigue life calcualtion

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