Issue 35

S. Boljanović et alii, Frattura ed Integrità Strutturale, 35 (2016) 313-321; DOI: 10.3221/IGF-ESIS.35.36 316   1 1 cos 0.9 b r     (11)   10 2 3 1 0.1 1 cos 1 a g t           (12) where  is angle location, t denotes a half of the thickness, r and w present radius of the hole and half-width of the lug, respectively. The propagation process of single crack emanating from a hole can be theoretically investigated by employing the relationship [1] expressed on the following way: 1 2 4 2 4 I I ab tr K K ab tr        (13) where  K I1 is the stress intensity factor range for single crack situation. Furthermore, the engineering maintenance inspections and controls show that the strength of lug under cyclic loading often can be threatened by through-the-thickness crack(s) initiated on the hole. The fatigue failure of such crack configuration can be analyzed through the stress intensity factor [17] expressed on the following way: 1 1 1 1 1 cos 2 IT w K S b f f G r w            (14) An angular function f  , the Bowie correction factor f 1 related to single semi-elliptical crack configuration, the pin-loaded correction factors G 1 , G 2 and the finite-width correction factors f w1 , f w2 for single and two-symmetric cracks, respectively, are discussed in Ref. [16, 18]. Then, the finite element method is used in order to evaluate the stress field around the crack tip, i.e. the stress distribution and the stress intensity factor. The propagation process of the semi-elliptical crack is numerically simulated by applying quarter-point (Q-P) singular finite elements [19], integrated in the software package MSC/NASTRAN [20]. All the computed results using both analytical and numerical methods are presented in next Section, Figure 1 : Geometry of the pin-loaded lug (Case 1 – through-the-thickness crack, Case 2 – one crack/two-symmetric cracks at a hole) .