Stress relaxation behaviour of glass fibre reinforced thermoplastic composites and its application to the design of interrupted in situ tensile tests for investigations by X-ray computed tomography

• Published in: Polymer testing Vol. 109; p. 107551
• Main Authors: Maurer, Julia, Jerabek, Michael, Salaberger, Dietmar, Thor, Michael, Kastner, Johann, Major, Zoltán
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-05-2022; Elsevier
• Subjects: Analytical model; Glass fibre reinforced polymers; Mechanical testing; Non-destructive testing; Stress relaxation; Analytical model; Stress relaxation; Mechanical testing; Glass fibre reinforced polymers; Non-destructive testing
• ISSN: 0142-9418; 1873-2348
• DOI: 10.1016/j.polymertesting.2022.107551

In situ investigations by X-ray computed tomography are widespread and have become very important for studying damage mechanisms in materials. Interrupted in situ tensile tests by X-ray computed tomography with laboratory devices have to be performed in displacement-controlled mode. In this regard, it is crucial to know at which point almost a steady state of the loaded specimen can be expected and thus an X-ray computed tomography scan at good data quality can be achieved. This study investigates the relaxation behaviour of injection moulded glass fibre reinforced polypropylene. Relaxation tests, according to a single loading and an interrupted in situ testing manner, are performed on different specimen geometries with varying fibre orientation distributions. An extension of the Kohlrausch-Williams-Watts function is used for modelling the relaxation behaviour. Two different approaches are presented in context of the proposed methodology. One approach is based on a look-up diagram and the other is the on-the-fly check during testing. The suggested methodology allows a coarse design and enables time saving optimizations of such in situ investigations.
•Different relaxation behaviour for single loaded and interrupted tested GFRPs.•Faster relaxation and greater decrease in stress for FOD perpendicular to load.•KWW function enables simple modelling of stress relaxation behaviour of GFRPs.•Methodology for coarse and time saving design of interrupted in situ tensile tests.