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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taking into account both analytical and numerical approaches, the failure behavior of damaged attachment lug subjected to cyclic loading is analyzed in the next Section.

4. Fatigue calculations by means of proposed fracture mechanics based model

Now the failure behavior of the pin-loaded lug with through-the-thickness crack under cyclic loading is theoretically examined to demonstrate the predictive capability of the proposed computational model. Such fatigue assessments, presented in the following Sections, take into account the stress analysis and the residual life calculation.

4.1. Stress analysis of the lug with initial through-the-thickness crack

The first example considers the crack propagation behavior of the through-the-thickness crack located at the lug hole (Fig. 1) through the stress field evaluation and the stress intensity factor estimation. The lug ( w = 83.3 mm, D =40 mm, t = 15 mm) is subjected to cyclic axial loading with constant amplitude ( P max = 63716 N, R = 0.1). In the failure analysis, two different heights of the lug head are taken into account here. Considered heights of the lug head and corresponding initial crack lengths are presented in Table 1. Further, for the damaged configuration, made of 7075 T7351 alloy, the following material parameters are assumed: S u = 432 MPa, ν = 0.3. Fatigue failure of the attachment lug with initial through-the-thickness crack at a hole is numerically here tackled by means of the MSC/NASTRAN software package. Thus, to describe a complex stress state field of such cracked situation, the quarter-point (Q-P) singular finite elements together with the two-dimensional finite elements are employed, step-by-step, for appropriate increments of crack length. A representation of the finite element mesh and the stress distribution are shown in Fig. 2a and b, respectively.

Fig. 2. Numerical analysis of the pin-loaded lug with through-the-thickness crack ( a = 4.16 mm, H = 57.1 mm): (a) finite element mesh; (b) stress distribution.

Table 1. Comparison of stress intensity factors for the lug with single through-the-thickness crack at a hole.

a (mm)

H = 57.1 mm Kmax ( MPam0 .5)

H = 44.4 mm Kmax (MPam0.5)

Analytical

FEM 20.80 21.84 36.47

Analytical

FEM 21.56 21.75 37.32

4/16 5.00

20.10 20.67 33.87

20.73 21.31 34.92

16.65