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

• Published in: Polymer testing 2018-09, Vol.70, p.544-555
• Main Authors: Schilling, Markus, Niebergall, Ute, Alig, Ingo, Oehler, Harald, Lellinger, Dirk, Meinel, Dietmar, Böhning, Martin
• Format: Article
• Language: English
• Subjects: Chemical compounds; Computed tomography; Crack propagation; Creep tests; Environmental stress cracking (ESC); Environmental testing; Fracture mechanics; Fracture surfaces; Full notch creep test (FNCT); Imaging; Imaging techniques; Laser scanning microscopy (LSM); Nondestructive testing; Polyethylene; Polyethylenes; Scanning acoustic microscopy; Scanning acoustic microscopy (SAM); Scanning microscopy; Slow crack growth (SCG); Stress cracking; Stress propagation; Test procedures; Tomography; X-ray computed tomography (CT)
• ISSN: 0142-9418; 1873-2348
• DOI: 10.1016/j.polymertesting.2018.08.014

Different imaging techniques were employed to monitor Full Notch Creep Test (FNCT) experiments addressing environmental stress cracking in more detail. The FNCT is a well-established test method to assess slow crack growth and environmental stress cracking of polymer materials, especially polyethylene. The standard test procedure, as specified in ISO 16770, provides a simple comparative measure of the resistance to crack growth of a certain material based on the overall time to failure when loaded with a well-defined mechanical stress and immersed in a liquid medium promoting crack propagation. Destructive techniques which require a direct view on the free fracture surface, such as light microscopy and laser scanning microscopy, are compared to non-destructive techniques, i.e. scanning acoustic microscopy and x-ray micro computed tomography. All methods allow the determination of an effective crack length. Based on a series of FNCT specimens progressively damaged for varied durations under standard test conditions, the estimation of crack propagation rates is also enabled. Despite systematic deviations related to the respective imaging techniques, this nevertheless provides a valuable tool for the detailed evaluation of the FNCT and its further development. •Fracture planes of FNCT specimens characterizing environmental stress cracking (ESC) behavior were analyzed by different imaging techniques.•Crack-lengths could be determined by these destructive and non-destructive imaging techniques.•Using a multiple sample technique, apparent crack-propagation rates could be estimated.•Systematic deviations were identified and discussed in the framework of the craze-crack mechanism underlying the ESC.