At the end of May, the SKZ Plastics Centre completed a pioneering research project, the aim of which was to develop a faster „test method with which the stress crack failure of plastic components under the influence of media can be assessed quantitatively“ for the first time. According to the SKZ, the new test concept enables „a well-founded prediction of service life“ for the first time. This is a major step forward for „quality assurance and product development in the plastics processing industry“.
„Stress crack failure, failure under the simultaneous effect of mechanical stress and chemical medium’ is the most common cause of damage to plastic components, according to SKZ. „The previously standardised methods, for example in accordance with ISO 22088“ usually only allow „a qualitative material ranking“ and have so far hardly enabled „a reliable prediction of service life.“
The project received funding from the German Federal Ministry for Economic Affairs and Climate Protection (Joint Industrial Research Programme/IGF).
Damage prevention for plastic components
„The method allows statements to be made about when a plastic fails under defined test conditions - such as medium (e.g. disinfectants, oils), load height and temperature“, says the SKZ, explaining the procedure. „The basis is a specially developed, heatable measurement setup that can be adapted to common universal testing machines. The test can be greatly accelerated in terms of time thanks to the targeted temperature increase (time-temperature superposition principle). The realised measurement setup with continuous force and strain measurement offers a particular advantage: in addition to failure times, the influence of stress duration and medium on the stiffness can also be investigated - for example through plasticiser effects. Processing-related factors such as residual stresses or molecular orientations can also be evaluated.“
Cooperation project also develops new testing device
In a complementary R&D cooperation project with the IPT Institut für Prüftechnik Gerätebau GmbH & Co. KG, a corresponding testing device with several measuring stations was developed, which currently has six independent measuring stations. The device enables „parallel tests with different media, plastics or test conditions (temperature, test type, test parameters)“ and is „now available at the SKZ for industrial applications in order to carry out (time-accelerated) tests for the quantitative assessment of the media stress crack resistance (failure times and creep deformation) of plastics“. The development of the measuring device was funded by the Central Innovation Programme for SMEs (ZIM).
Further information
Final report „Medienbedingtes Spannungsrissversagen“
