Untersuchung von quasi-spröden Schädigungsmechanismen in zyklisch und statisch belasteten Prüfkörpern aus Polyethylen

Translated title of the contribution: Investigations of quasi brittle failure mechanisms in cyclically and statically loaded polyethylene specimen

Katharina Bruckmoser

Research output: ThesisMaster's Thesis


The long-term failure behavior of pressurized pipes made of polyethylene (PE) is characterized by the resistance against crack initiation and slow, quasi-brittle crack growth. A deeper understanding of polymers and enhanced materials lead to modern PE pipe grades with significantly improved long-term properties. However, this improved material behavior induces new challenges in the field of material testing regarding reasonable testing times. Methods of the linear elastic fracture mechanics (LEFM), in particular in combination with cyclic tests on Cracked Round Bar (CRB) specimens, show promising results for a time optimized material characterization. This thesis deals with a systematic fracture surface analysis of cyclically and statically loaded test specimens with different geometries made of two different types of high density polyethylene (PE-HD). In addition to the CRB specimens, Compact Tension (CT) as well as pressurized pipes were examined. Characterization of the fracture surfaces was done by means of light and scanning electron microscopy, the general suitability of three-dimensional topographic measurement methods was evaluated as an addition to a fracture surface analysis. Based on the concept of the stress intensity factor (SIF) of the LEFM and the Dugdale model, which describes the formation of plastic zones, the fracture surfaces were investigated with regard to the crazefibrils as a function of R ratio (R = minimum / maximum load), specimen geometry and the different materials studied. It turned out that the height of the crazefibrils increases with increasing SIF, and increasing R ratio. A comparison of the fracture surfaces of the different specimen geometries at locations of comparable SIF showed a differing appearance. This mainly reflects the influence of the varying amount of three-dimensionality in the stress state in the specimen geometries, thus affecting the slow crack growth in PE. Furthermore, material specific differences in craze fibril length could be detected at locations of identical SIF. In addition to a quantitative assessment of the height of crazefibrils, topographic measurements allowed a detailed investigation of arrest lines on PE fracture surfaces. It was shown that the distance between the arrest lines increases with increasing SIF. Furthermore, a method for investigating the plastic zone of CRB specimens, combining the advantage of optimized testing times and systematic crack tip analysis, was developed. Thereby the crack growth process was stopped before, during and after crack initiation and the specimens were prepared for microscopic analysis enabling a material and time dependent characterization of the crack growth behavior.
Translated title of the contributionInvestigations of quasi brittle failure mechanisms in cyclically and statically loaded polyethylene specimen
Original languageGerman
  • Frank, Andreas, Co-Supervisor (external)
  • Pinter, Gerald Gerhard, Supervisor (internal)
Award date17 Dec 2010
Publication statusPublished - 2010

Bibliographical note

embargoed until null


  • fracture surface analysis
  • crack growth initiation
  • crack growth
  • crazing
  • stress intensity factor
  • pressurized pipes
  • crack tip analysis

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