PSI - Issue 37

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Mohammed Algarni et al. / Procedia Structural Integrity 37 (2022) 676–683 Mohammed Algarni/ Structural Integrity Procedia 00 (2019) 000 – 00

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Figure 1: (a) 3D printed specimens with different notches. (b) Specimen dimensions definition.

3. Experimental Results A summary of the experimental fatigue results is plotted on a log-normal S a - N f chart, as shown in Figure 2, where S a and N f are the amplitude stress and the number of fatigue life cycles to full fracture, respectively. Figure 2(a) shows the influence of the notches on PLA fatigue life with zero mean stress ( R = -1, S m = 0). Figure 2(b) and Figure 2(c) show the influence of the notches on PLA fatigue life with different positive mean stresses where the load ratio R was 0.1 ( S m = 1.22 S a ) and 0.3 ( S m = 1.86 S a ). The charts clearly show that the fatigue life of the PLA specimens decreased as the notch radius decreased. Therefore, the notch effect (or stress concentration) should be considered when designing parts, as the experimental results show more than 50% fatigue life reduction, owing to the stress concentration. Additionally, the effect of mean stress on the fatigue life is shown in Figure 2(d – f) with different notches. The charts show that increasing mean stress also reduced the fatigue life. The experimental results showed that the mean stress effect had less influence on fatigue life in the high cycle fatigue (HCF) regime than in the LCF regime. Also, the slope of the S a - N f curve slightly steepens as the mean stress increases.