Zyklische Risswachstumsversuche an CRB-Proben als Qualitätssicherungstest zur Abschätzung des Langzeitverhaltens von PE-Rohrwerkstoffen

Translated title of the contribution: Cyclic crack growth tests with CRB-specimens as a quality assurance tool for assessment of longtime behavior of PE pipe grades

Anita Redhead

Research output: ThesisMaster's Thesis

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Abstract

In this thesis different PE pipe grades and lots were investigated by the cyclic CRB method. The aim was to enhance the test sensitivity and proof its applicability for a quick quality assurance method that is able to assess different molecular and morphological effects and lot to lot variations on slow crack growth (SCG). So, various molecular and morphological characterizations were necessary. The concentration of the comonomer was investigated by Infrared spectroscopy, molecular mass distribution by size exclusion chromatography (SEC) and crossover-points (intersection of storage and loss modulus) by rheological experiments. Molecular mass was found indirectly by determination of the melt flow rate (MFR) and length and concentration of side chains was identified indirectly by isothermal crystallization experiments. Small angle X-ray scattering and wide angle X-ray scattering (SAXS, WAXS), dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC) and density were adopted for characterization of morphology. Thermal mechanical analysis (TMA) offered valuable results to status of orientations and effects of variable compression moulding parameters. Investigations of the resistance against SCG were realized by the cyclic CRB method and in addition rapid crack propagation (RCP) by instrumented Charpy impact tests. The cyclic CRB method allowed a ranking of the different PE pipe materials and lots concerning resistance against SCG with testing times less than 100 hours per material and testing machine. It was possible to perform the ranking as a function of failure time as well as of crack initiation time that gave another reduction of testing time of about 50 %. The ranking identified by the cyclic CRB method corresponded to the expectations based on the molecular and morphological properties of the materials. In particular it was remarkable that effects of only minor changes in the molecular mass distribution and the concentration of the co-monomer in case of lot to lot variations could be proven reliably and as expected. Concerning effects of lot to lot variations, the ranking found by the cyclic CRB method was consistent to the rankings identified by MFR-, density- and isothermal crystallization-experiments, making these methods to possible quality standards within one type of material. Although generally other molecular processes are responsible for rapid crack growth, the ranking found by instrumented Charpy impact tests was corresponding to the one determined by the cyclic CRB method.
Translated title of the contributionCyclic crack growth tests with CRB-specimens as a quality assurance tool for assessment of longtime behavior of PE pipe grades
Original languageGerman
QualificationDipl.-Ing.
Supervisors/Advisors
  • Pinter, Gerald, Supervisor (internal)
Award date18 Dec 2009
Publication statusPublished - 2009

Bibliographical note

embargoed until null

Keywords

  • fatigue CRB method PE pipe grades resistance against slow crack growth lot to lot variations

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