Novel Solar Thermal Collector Systems in Polymer Design – Part 5: Fatigue Characterization of Engineering PA Grades for Pressurized Integrated Storage Collectors

A novel aging test method considering the superimposed mechanical and environmental (temperature and environmental medium) loads representative for pressurized integrated storage collectors (ICS) is described. Engineering polyamide (PA) grades with short glass fiber (GF) reinforcement, which are of high relevance for endcaps of steel-pipe ICS absorbers or all-polymeric absorber/storage-tanks, are characterized on a specimen level. Therefore, specific test devices and test arrangements for fracture mechanics specimens with or without weld-line are implemented on an electro-dynamic test machine. Fatigue crack growth kinetics data are obtained by conducting cyclic mechanical loads under various environmental testing conditions. The experimental results of two glass-fiber reinforced PA grades, using compact type specimens, performed at two different temperatures (23 °C and 80 °C) and in two environmental media (air and water), are compared in terms of crack growth kinetics. Moreover, the influence of welding on the crack growth kinetics for one PA grade is shown. For all specimens (unwelded and welded) the fatigue crack growth rates are enhanced in water compared to air. In welded specimens the fatigue crack growth resistance is significantly reduced compared to unwelded specimens.