Characterization of irradiation crosslinked polyamides for solar thermal applications – Fatigue properties

Abstract In this research, the influence of electronic beam irradiation on the fatigue crack growth (FCG) behavior of unreinforced polyamide 66 (PA 66) and two glass fiber reinforced PA 66 (30 w% glass fiber content, 35 w% glass fiber content) was investigated. In total, five different doses in the range of 0 kGy and 200 kGy were applied. While previous research covered the influence of irradiation on basic thermo-analytical characteristics and thermo-mechanical properties of these PA material grades, the present paper deals with the effect of irradiation crosslinking on the FCG performance. To cover the relevant range of service environmental conditions, the FCG investigations were performed for two different application near material states “as-received” and “water saturated” at 23 °C and 80 °C, respectively. For the water saturated material states, the tests were conducted with specimens under simultaneous water immersion. For this purpose, specific test devices and test arrangements were designed, built and implemented on an electro-dynamic test machine. In general, a change in the material state and test conditions from 23 °C in air with as-received specimens (fatigue testing occurs below the materials glass transition temperature TG) to 80 °C in water with water saturated specimens (fatigue testing occurs above the materials TG) led to a significant reduction in the FCG resistance. Furthermore, while for unreinforced PA 66 no significant effect of irradiation on FCG kinetics was detected for the as-received state at 23 °C (i.e., below TG), irradiation had a detrimental influence on the fatigue behavior at 80 °C for the water saturated material state (i.e., above TG). Interestingly, quite the opposite effect of irradiation on FCG resistance was found for glass fiber reinforced Pas. The irradiation caused a reduction in the FCG resistance for as-received material states at 23 °C, while hardly any effect of irradiation was detected for the water saturated materials at 80 °C.