PSI - Issue 39

Slobodanka Boljanović et al. / Procedia Structural Integrity 39 (2022) 624 – 631 Slobodanka Boljanović et al. / Structural Integrity Procedia 39 (2022) 624 – 631

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4.2. Driving mode simulation under cyclic loading

Fatigue endurance evaluations presented in this Section examine the plate failure due to the elliptical corner damage (Fig. 1b) in terms of the crack growth path, adopting maximum stress and stress ratio equal to P max = 65000 N and R = 0.1, respectively. A surface stress raiser, whose initial sizes are equal a 0 = 1.6 mm, b 0 = 2.2 mm in depth and surface crack growth directions, is located in the plate made of 2024T3 aluminium alloy ( C A = C B = 6×10 -10 , w = 70 mm, t = 8 mm). Knowledge of micro-notch mechanisms and their impact on the fatigue strength enable the bearing capacity improvements of moving systems. Therefore, driving force interactions are theoretically examined here through the crack growth progression, combining Eq. (1) with Eq. (3)-(12). Evaluated crack growth paths are shown in Fig. 4a and 4b in the case of eight different crack lengths (please see Figure caption) in depth direction, and appropriate horizontal axis and vertical axis that correlate with the front face and the left edge of the plate, respectively.

Fig. 4. Crack path evolutions ( R = 0.1): (a) 1 – a = 2.4 mm, 2 – a = 2.8 mm, 3 – a = 4.0 mm, 4 – a = 4.3 mm and (b) 1 – a = 5.1 mm, 2 – a = 5.6 mm, 3 – a = 6.7 mm, 4 – a = 7.1 mm. Calculated curves are the present outcomes.

4.3. Fatigue strength evaluation and effects of cyclic loading and plate thickness Finally, the failure performance of the elliptical corner crack (Fig. 1b) is explored taking into account the effect of applied cyclic loading. In this regards, the plate life was assessed in the case of three different values of maximum force P max = 50225 N, 45659 N, 41508 N, with stress ratio R = 0.2, assuming width and thickness of the plate equal to w = 70 mm, t = 4.5 mm, respectively, and initial crack lengths equal to a 0 = 1.23 mm, b 0 =1.78 mm in depth and surface directions. Further, the driving mode analysis was performed here for damaged plates ( w = 70 mm, a 0 = 1.45 mm, b 0 = 1.9 mm, P max = 60200 N, R = 0.1) whose thicknesses are equal to t = 4 mm, 5.2 mm, and 6.76 mm, respectively. Note that all plates are made of 2024T3 aluminium alloy, and the same material parameters were employed as those examined in the previous Section. Fatigue strength degradation is assessed through the residual life using novel damage tolerance-based computational framework, as is discussed in previous Sections. Generated number of loading cycles versus crack length in the case of damaged plate subjected to three different values of maximum forces and relevant estimates for three different plate thicknesses are shown in Fig. 5a, 6a, and 5b, 6b with respect to depth and surface crack growth directions. From the safety-relevant analysis displayed in Fig. 5 and Fig. 6, it can be inferred that, if the value of maximum stress decreases by 10%, the life to failure increases by 33%, while the life increases by more than two and a half times for the part-through flaw examined by increasing the plate thickness by 30%.