Issue 35

H. Dündar et alii, Frattura ed Integrità Strutturale, 35 (2016) 360-367; DOI: 10.3221/IGF-ESIS.35.41 366 The plate is under displacement controlled cyclic loading. 0.005 mm displacement is applied at the bottom area of the plate to ensure tension loading and top area is fixed. Al-7075 is chosen as material of the plate and modulus of elasticity and Poisson’s ratio are 72000 MPa and 0.33, respectively. Material constant n is 1.34 and fracture toughness is 23.9 MPa m for the material [17]. Thickness of the plate is taken as 3 mm to simulate plane stress conditions. Having performed crack propagation analyses using the same procedure employed in the first application, obtained results are compared to those from Judt and Ricoeur’s [17] study. Comparison of crack paths between FCPAS and Ref. [17] is shown in Fig. 8. As can be seen from Fig. 8, eccentricity of the cracks causes shear stress and therefore, K II SIFs. Thus, cracks change their direction from the horizontal plane. Vertical distance between 2 nd and 3 rd cracks are very small and therefore, SIFs in this region are higher than the region around the 1 st crack. As a result, 2 nd and 3 rd cracks propagate faster than the 1 st crack, which propagate at a slower rate. Comparisons of equivalent SIF vs. number of crack growth steps, as given in Ref. [17], are shown in Fig. 9. It should be noted that, in the current analyses, much less number of increments (17 steps) are used compared to Ref. [17] (325 steps). Equivalent SIFs are calculated using Eq. (7) [17].   2 2 1 1 4 2 2 I e I II K K K K     (7)  I =1.155 [17], K I and K II are mode-I and mode-II stress intensity factors. Figure 9 : SIF comparison between FCPAS and Ref. [17]. Fig. 8 and Fig. 9 show that FCPAS results are very close to those of Judt and Ricoeur [17] in terms of crack paths and SIF vs. number of crack growth steps. Therefore, this case serves as a second validation problem for application of FCPAS crack propagation analysis procedures to multiple cracks in thin-walled structures growing in a non-planar manner. C ONCLUSIONS n this study, three-dimensional non-planar crack propagation analyses for thin-walled structures were performed using FCPAS (Fracture and Crack Propagation Analysis System). Two case studies related to multiple cracks with non-planar growth were presented. Results of these studies in terms of crack paths and stress intensity factor variations with number of cycles showed good agreement with analysis data from the literature. Thus, it was concluded that non-planar growths of multiple cracks in thin-walled structures can accurately be simulated using FCPAS. Further developments in FCPAS to be able to analyze non-planar crack growth of surface and corner cracks under mode-I, II and III conditions are planned as future studies. I