Issue 35

O. Demir et alii, Frattura ed Integrità Strutturale, 35 (2016) 330-339; DOI: 10.3221/IGF-ESIS.35.38 333 FRAC3D, a general-purpose finite element based 3-D fracture analysis program, employs enriched crack tip elements to compute the stress intensity factors. The enriched finite elements do not require special mesh near crack front and stress intensity factors are directly solved for at the same time as nodal displacements without any post-processing effort. Further technical details related to three-dimensional enriched elements are given in [16, 17]. 25 mm-thick CTS specimens are used during the preliminary design stage of mixed-mode clevises. Results of stress and fracture analyses of CTS specimens (25 mm thick) for all loading angles showed that required loads to fracture the specimens (25 mm thick) are very high especially for highly mode-II conditions (60°, 75° and 90°). Therefore, 10 mm-thick specimens are used in experimental analyses. Some sensitivity analyses were performed in a previous study [18] to investigate the effect of boundary conditions and loads, contact type and friction coefficient between contact surfaces used in the analyses on the computed SIFs. The results from this study is summarized in Fig. 5. Firstly analyses were performed to check the linearity between the increment of applied loads on the clevises and the increment of stress intensity factor (Fig. 5 (a)). It can be clearly seen from the figure that there is a linear relation between the SIFs and the applied loads in the range considered. Frictional (0.2 friction coefficient), no separation, bonded and bonded (always) contact types were used respectively (Fig. 5 (b)) and also different friction coefficients (0.1, 0.2, 0.3 and 0.4) were used (Fig. 5 (c)) under constant loading angle (45 degrees) and load value (10 kN) to investigate the contact type effect on SIFs. Results showed that nearly there is no difference between the different cases of contacts and SIFs along the crack front are almost identical between the analyses with different friction coefficients. In Fig. 6, a process map is given to summarize the analysis procedure. 0 5 10 15 20 25 30 0 2000 4000 6000 8000 10000 12000 14000 SIF ((M Pa·m ½ ) Load(N) 0.0 1.0 2.0 3.0 4.0 5.0 6.0 1 3 5 7 9 11 13 15 17 19 21 SIF ((M Pa·m ½ ) CrackTipNode 0.2Friction, KI Bonded, KI Bonded(always), KI NoSeperation, KI 0.0 0.5 1.0 1.5 2.0 2.5 1 3 5 7 9 11 13 15 17 19 21 SIF ((M Pa·m ½ ) CrackTipNode 0.1 fric. coef. KII 0.2 fric. coef. KII 0.3 fric. coef. KII 0.4 fric. coef. KII (a) (b) (c) Figure 5 : Sensitivity analyses to investigate the effect of (a) boundary conditions and loads, (b) contact type and (c) friction coefficient between contact surfaces used in the analyses on the computed SIFs. Figure 6 : Process map of the analysis procedure.