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Crack propagation in PE-HD induced by environmental stress cracking (ESC) analyzed by several imaging techniques

: Schilling, Markus; Niebergall, Ute; Alig, Ingo; Oehler, Harald; Lellinger, Dirk; Meinel, Dietmar; Böhning, Martin


Polymer testing 70 (2018), pp.544-555
ISSN: 0142-9418
Journal Article
Fraunhofer LBF ()
enviromental stress cracking; slow crack growth; full notch creep test; laser scanning microscopy; scanning acoustic microscopy; x-ray computed tomography; ESC; SCG; FNCT; LSM; SAM; CT

Different imaging techniques were employed to monitor Full Notch Creep Test (FNCT) experiments addressingenvironmental stress cracking in more detail. The FNCT is a well-established test method to assess slow crackgrowth and environmental stress cracking of polymer materials, especially polyethylene. The standard testprocedure, as specified in ISO 16770, provides a simple comparative measure of the resistance to crack growth ofa certain material based on the overall time to failure when loaded with a well-defined mechanical stress andimmersed in a liquid medium promoting crack propagation.Destructive techniques which require a direct view on the free fracture surface, such as light microscopy andlaser scanning microscopy, are compared to non-destructive techniques, i.e. scanning acoustic microscopy and xraymicro computed tomography. All methods allow the determination of an effective crack length. Based on aseries of FNCT specimens progressively damaged for varied durations under standard test conditions, the estimationof crack propagation rates is also enabled. Despite systematic deviations related to the respective imagingtechniques, this nevertheless provides a valuable tool for the detailed evaluation of the FNCT and its furtherdevelopment.