Charakterisierung des Risswachstumsverhaltens von Cracked Round Bar (CRB) Prüfkörpern auf Basis der Materialnachgiebigkeit

Translated title of the contribution: Characterization of the crack growth kinetics in Cracked Round Bar (CRB) specimens based on material compliance

Werner Freimann

Research output: ThesisMaster's Thesis

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Abstract

Pressurized pipes made of polyethylene (PE) have been used for more than 40 years, especially in fuel gas and water supplying systems. The assessment of the essential lifetime of those pipes, which is at least 50 years, is based on internal pressure test and the standard extrapolation method by EN ISO 9080. The generally accepted critical failure mechanism of PE pipes under long term applications is characterized by slow crack growth (SCG). Based on the methods of the linear elastic fracture mechanics (LEBM) it is possible to determine the ki-netics of brittle crack growth with specimen tests and to translate it into real components like pipes. As a result of the constant development of the basic materials, especially by the variation of the molecular mass distribution and by the selective placement of short chain branches, PE pipe materials with significantly increased crack resistance are available today. Due to this increased material performance, on the one hand discussions concerning operation times of 100 years have been started and on the other hand test methods have to be optimized to characterize failure of the modern materials in accellerated times. One possibility to reduce testing times is offered by fatigue loading due to an increased tendency of slow crack growth under this loading mode. Another potential to reduce testing times is the geometrie of the specimens. Regarding the geometry cracked round bar (CRB) specimens are helpful to decrease testing times by there high constraint and fast crack initiation. Because of the high tendency to excentric crack growth in this specimen a direct meassurement of the crack growth rate was not possible so far, the development of an reproduceable method to meassure the crack kinetics in CRB specimens under cyclic loadings was the main part of this master thesis. For this purpose the crack opening displacement was measured with three evenly distributed extensometers for different initial crack lengths to get a crack length dependent compliance calibration curve. Using this calibration curve it was possible to determine the crack kinetics for CRB specimen within a single test. Moreover, attention was directed to the analysis of crack initiation, which can be assigned accurately with the three extensometer signals. The developed testing method was applied to four different PE types and the potential of crack initiation for material ranking was also evaluated.
Translated title of the contributionCharacterization of the crack growth kinetics in Cracked Round Bar (CRB) specimens based on material compliance
Original languageGerman
QualificationDipl.-Ing.
Supervisors/Advisors
  • Pinter, Gerald, Supervisor (internal)
Award date27 Jun 2008
Publication statusPublished - 2008

Bibliographical note

embargoed until null

Keywords

  • fatigue test CRB specimen compliance crack initiation crack growth kinetics slow crack growth polyethylene pipes

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