Media-related stress cracking failure
Accelerated prediction of the stress cracking failure of plastics in different media
Project duration
From: 01.07.2022 To: 30.10.2024Description
Environmental stress cracking (ESC) is responsible for 25% of plastic component failures and is therefore of high economic relevance. The formation of stress cracks has been the subject of research for a long time, but no suitable test method has yet been found that can be used for the quantitative design of plastic components in contact with potentially stress-cracking media. In contrast to the various already standardized stress cracking test methods (e.g. ISO 22088 series of standards), which generally only enable material ranking, the new test concept can be used explicitly for quantitative service life prediction. The developed and validated test and evaluation concept makes it possible to determine the time after which a plastic will fail under which conditions in terms of load level, medium and temperature. A measurement setup for mechanical testing in (heatable) media was designed and implemented, which can be adapted to commercially available universal testing machines. The use of elevated temperatures enables accelerated testing according to the time-temperature-superposition principle. The measurement setup realized with continuous force and strain measurement offers the great advantage that not only failure times can be determined, but also the influence of stress duration and medium on the stiffness can be evaluated. This also makes it possible to identify a potential plasticizer effect caused by the medium. The new testing and evaluation concept can also be used to evaluate processing-related influencing factors such as residual stresses and molecular orientations. In particular, SMEs that cannot afford the otherwise necessary time-consuming and costly long-term tests benefit from the time-saving test concept for quantitative service life prediction.
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