Various methods are used to characterize the deterioration of mechanical properties in polymers. The focus is set on distinguishing between time-dependent and irreversible damage in two different grades of polypropylene. First, digital image correlation is utilized to capture the stress–strain behavior during monotonic tensile tests. Changes in specimen volume are recorded throughout the experiment and serve as an indicator for crazes and voids. However, the elastic modulus, E, cannot be monitored throughout the entire experiment. Further analysis is performed in the form of cyclic load–unload tests. E and the residual strain, εres, as a function of the applied strain, εappl, are obtained for each cycle. Results show that E primarily suffers from the time-dependent behavior of the tested polymers in this case. Subsequently, an alternative technique is applied, where specimens are prestrained and then allowed to relax. In the following dynamic mechanical analysis, viscoelastic effects can be avoided. Considerations on the onset and evolution of damage are made. Ultimately, these results are confirmed through microcomputed tomography, where the shapes and densities of defects are captured in high resolution.
Bibliographical noteFunding Information:
This research was supported by the Austrian Research Promotion Agency (FFG) as part of the project “Entwicklung und Optimierung von hoch risszähen, polymeren Mehrschicht‐Verbundsystemen nach biomimetischen Prinzipien,” grant agreement 858562, referred to with the acronym “BioMimicPolymers.” CT scans and evaluations were performed within the projects “BeyondInspection (grant number: 874540)” and “pore3D (grant number: 868735).” Both CT projects were funded by the State Government of Upper Austria and Austrian Research Promotion Agency (FFG).
© 2022 The Authors. Polymer Engineering & Science published by Wiley Periodicals LLC on behalf of Society of Plastics Engineers.
- computed tomography
- elastic modulus decay