PSI - Issue 5

Slobodanka Boljanović et al. / Procedia Structural Integrity 5 (2017) 801 – 808 Slobodanka Boljanović, Stevan Maksimović / Structural Integrity Procedia 00 (2017) 000–000

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Further, in the present stress analysis of the damaged attachment lug the stress intensity factor is calculated by applying fracture mechanics based analytical model, discussed in Section 3. For two different locations of the lug hole with respect to the top of lug head, computed values of the stress intensity factor, by employing Eqs.(4)-(8) and the finite element method, are presented in Table 1. Such a comparison shows that calculations obtained through developed analytical model are in accordance with those results in which the finite element method is applied.

4.2. Residual life assessment for the attachment lug

Now the fatigue strength of the lug with single through-the-thickness crack (Fig. 1) is tackled. In this failure analysis, four different lugs subjected to cyclic loading with constant amplitude, made of 7075 T651 alloy ( C =2.55×10 -10 , m = 3.06), are taken into account. For all pin-loaded lugs ( t = 12.7 mm, a 0 = 0.635 mm) examined, geometrical sizes and loading parameters are presented in Table 2. The residual strength of fatigue critical lug is theoretically analyzed here through the stress intensity factor calculation by employing Eqs.(4)-(8). Then, in order to estimate the life to failure Eq. (3) is employed. The fatigue assessments for the lug subjected to two different stress ratios R = 0.5 and R = 0.1, are shown in Fig. 3 and 4, respectively. Further, all computed results for number of loading cycles to failure are compared with relevant experimental data, reported by Kathiresan and Brussat (1984). From such comparisons, presented in Figs. 3 and 4, it can be deducted that the estimations obtained here are in a fairly good correlation with available experimental results.

Table 2. Geometry and external loading parameters for the damaged lug (Kathiresan and Brussat (1984)). Lug ID w (mm) D (mm) R Pmax (N) ABPL84, ABPL91 114.3 38.1 0.5 60071 ABPL47, ABPL94 85.7 38.1 0.5 45053 ABPL48, ABPL92 85.7 38.1 0.1 112632 ABPL46, ABPL93 85.7 38.1 0.1 45053

Fig. 3. Crack length against number of loading cycles to failure for the lug with through-the-thickness crack ( R = 0.5): (a) w = 114.3 mm (Experiment 1 – ABPL84, Experiment 2 – ABPL91); (b) w = 85.7 mm (Experiment 1 – ABPL47, Experiment 2 – ABPL94). Experimental results are reported by Kathiresan and Brussat (1984).