Einfluß der Temperatur auf Ermüdung und Bruch
von D. G. Young u. J. A. Danik
Although fatigue tests at varied temperatures are not common due to the added burden of testing, there are times when variable temperature testing is important to ensure that rubber compounds will be suitable for the full range of use conditions. This is particulary true when materials with high Tg (> -50°C) are being considered for use in tires. Results for two high Tg rubber compounds (ECO and HS-SBR) showed fatigue crack growth (FCG) rates that were roughly 100 times those of a BIIR liner compound over the temperature range of -25 to 100°C. Additional tests with BIIR and NR showed that the most crack growth results for temperatures of -25°C to 100°C, and various strains, followed similar fatigue functions (dc/dn vs. T). The exception was some data for NR at 0 and -25°C which showed inhibited rates of FCG due to strain crystallization. There appears to be a window of strain rate, temperature and strain level where this effect is noticed, but these results need to be confirmed for NR and other strain crystallizable elastomers. Two fully cured NR beld skims used in truck tires showed linear results for log dc/dn vs. log T at temperatures of 70 to 100°C. However, undercured samples of one compound exhibited more temperature sensitivity of FCG results; specifically, rates of FCG increased significantly with temperature at low strain levels. This suggests the need for further evaluation of the effect of cure state on FCG over a range of test temperatures.