PSI - Issue 41

Slobodanka Boljanović et al. / Procedia Structural Integrity 41 (2022) 704 – 711 Slobodanka Bo ljanović et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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4.3. Crack-shape impact on the fatigue strength

Finally, fatigue evaluations herein presented tackle the stability of the plate ( t = 6 mm, w = 60 mm, Fig. 1b) taking into account the crack shape effect. Such a stress raiser analysis has been performed for three initial corner flaws (whose crack growth lengths in depth and surface directions are equal to a 0 = 1.25 mm, 1.56 mm, 1.95 mm and b 0 =2.02 mm), assuming maximum force and stress ratio equal to P max = 37000 N and R = 0.2, respectively. Further, the failure strength has been estimated in the case of three plates ( w = 60 mm, P max = 31000 N, R = 0.3) with thicknesses equal t = 3.5 mm, 4.2 mm and 5.04 mm, and initial flaw characterized by a 0 = 1.14 mm, b 0 =1.37 mm in two critical directions. Targeting on the damage tolerance-based design discussed through this research, the fatigue interactions of safety-critical flaws have been quantified in terms of the number of loading cycles. Life estimates obtained in the case of three elliptical crack shapes examined and those for three plate thicknesses are shown in Fig. 6a, 7a and Fig. 6b, 7b, as a function of depth and surface crack growth direction, respectively.

Fig. 6. Fatigue strength analysis ( R = 0.2): (a) a vs. N and (b) b vs. N (1 - a 0 = 1.25 mm, 2 - a 0 = 1.56 mm, 3 - a 0 = 1.95 mm). Calculated curves generated within the present research.

Fig. 7. Fatigue strength analysis ( R = 0.3): (a) a vs. N and (b) b vs. N (1 - t = 3.5 mm, 2 - t = 4.2 mm, 3 - t = 5.04 mm). Calculated curves generated within the present research.