PSI - Issue 57

5

Martin Matušů et al. / Procedia Structural Integrity 57 (2024) 327 – 334 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Fatigue experiments that were conducted in this campaign had the condition to end the experiment when any of these limits is exceeded: • Frequency drops by 10 Hz. • Load amplitude changes by ± 0.5 kN. • Static loads changes by ± 0.5 kN. • 10 7 cycles are reached. These specimens are classified as run-outs. Such specimens were then subjected to another subsequent cyclic loading with two times higher load amplitude at least.

Fig. 3. S-N curves of the four groups of specimens based on the heat treatment.

In Fig. 3, it can be observed that the lowest fatigue performance was exhibited by NoHT series, which was not subjected to any heat treatment. This outcome was anticipated as there is no residual stress relieve after printing. The performance of the series subjected to any heat treatment is superior in all cases demonstrated in this study. Series T200 and T240 exhibit nearly identical fatigue performance in the range from 1e5 to the fatigue limit domain. The LCF (Low cycle fatigue) region below 100,000 cycles indicates that the series subjected to T200 HT demonstrates higher fatigue strength. T300 series subjected to heat treatment at 300 °C results in the highest fatigue limit. In this case however, the worst fatigue performance is observed in the transition to LCF domain. This response can be attributed to the decomposition of the silicon network. For fatigue regression, the Kohout- Věchet [10] model is used which well represents the transition from LCF to HCF and the transition to the fatigue limit domain – see the curves in Fig. 3. Overall results show us that the fatigue strength performance and tensile performance is the best for T300 series with heat treatment at 300 °C. The lowest scatter of experimentaldata was also observed for this T300 series. It should be pointed out however, that the T200 heat treatment leads to best fatigue performance at lower lifetimes below 50,000 cycles approximately.

2.3. Thermal response

The temperature evolution on the specimen's surface was measured using the infrared thermal cameras to investigate the thermal response of cyclically loaded specimens. The research findings are presented briefly below. Main references for our research here are papers by Torabian et. al [11] and by Meneghetti [12]. This heat equation represents our focused problem: