PSI - Issue 28

Slobodanka Boljanović et al. / Procedia Structural Integrity 28 (2020) 2370 – 2377 Slobodanka Boljanović et al. / Procedia Structural Integrity 00 (2020) 000 – 000

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4.2. Modeling of the surface corner crack growth Now fatigue evaluations tackle the driving mode progression in terms of the crack growth path. The plate with quarter-elliptical corner crack, made of 2024 T3 ( w = 60 mm, t = 9 mm, a 0 = 1.7 mm , b 0 = 2.3 mm, Fig. 1b), is exposed to constant-amplitude cyclic loading ( P ma x = 50000 N, R = 0.1). In the failure analysis presented here, the behavior of a crack-like corner flaw often induced by manufacturing/environmental factors is assessed by combining the crack growth rate and stress intensities in the vicinity of the crack tip through Eqs. (1) to (10). The driving mode progression is theoretically examined through ten different crack growth lengths in depth direction, as is shown in Fig. 4a and 4b (where the horizontal axis coincides with the front face and the vertical axis matches with the left edge of the plate).

Fig. 4. Crack growth path evaluations: (a) 1 – a 0 = 2.5 mm, 2 – a 0 = 3 mm , 3 – a 0 = 4 mm, 4 – a 0 = 4.6 mm, 5 – a 0 = 4.9 mm; (b) 1 – a 0 =5.5 mm, 2 – a 0 = 6.2 mm, 3 – a 0 = 7.3 mm, 4 – a 0 = 7.9 mm, 5 – a 0 = 8.3 mm, calculated curves are the present results.

4.3. Failure of the plate and effects of crack shape and stress ratio Finally, through the residual strength analysis presented, the effects of crack shape and stress ratio are examined under cyclic loading. In this regard, the fatigue life of the plate ( w = 50 mm, t = 9 mm, Fig. 1b) subjected to maximum force equal to P ma x = 112500 N, with stress ratio R = 0.1, is assessed in the case of three different corner cracks, whose sizes in depth and surface directions are equal to a 0 = 0.9 mm , 1.35 mm, 2.02 mm and b 0 = 2.07 mm, respectively. Moreover, the stability of a quarter-elliptical corner crack ( a 0 = 1.85 mm , b 0 = 2.1 mm) in the plate ( w =50 mm, t = 8 mm, P ma x = 120000 N, R = 0.1) is herein evaluated for three different stress ratios ( R = 0.1 , 0.25 and 0.625). Since all plates are made of 2024 T3 aluminum alloy, the same material parameters are used as those mentioned in Section 4.1. Safety-relevant analysis of plates with a quarter-elliptical corner flaw is performed employing Eqs. (1) to (11). Calculated number of loading cycles, as a function of crack length in depth and surface directions, is shown in Fig. 5a, 5b, and Fig. 6a, 6b, respectively. From these Figures where the effects of crack shape and stress ratio are examined, it can be concluded that geometrical and load parameters may seriously compromise the fatigue strength of the damaged plate-type component.