Issue 35

M. Bozkurt et alii, Frattura ed Integrità Strutturale, 35 (2016) 350-359; DOI: 10.3221/IGF-ESIS.35.40 350 Focussed on Crack Paths Finite element modeling and experimental studies on mixed mode-I/III fracture specimens M. Bozkurt, A. O. Ayhan, M. F. Yaren, S. İriç Department of Mechanical Engineering, Sakarya University, 54187, Sakarya, Turkey murat.bozkurt3@ogr.sakarya.edu.tr, ayhan@sakarya.edu.tr , myaren@sakarya.edu.tr , siric@sakarya.edu.tr A BSTRACT . In this study, finite element modeling and experimental studies on a mode-I/III specimen similar to the compact tension specimen are presented. By using bolts, the specimen is attached to two loading apparatus that allow different levels of mode-I/III loading by changing the loading holes. Specimens having two different thicknesses are analyzed and tested. Modeling, meshing and the solution of the problem involving the whole assembly, i.e., loading devices, bolts and the specimen, with contact mechanics are performed using ANSYS TM . Then, the mode-I/III specimen is analyzed separately using a submodeling approach, in which three- dimensional enriched finite elements are used in FRAC3D solver to calculate the resulting stress intensity factors along the crack front. In all of the analyses, it is clearly shown that although the loading is in the mode-I and III directions, mode-II stress intensity factors coupled with mode-III are also generated due to rotational relative deformations of crack surfaces. The results show that the mode-II stress intensity factors change sign along the crack front and their magnitudes are close to the mode-III stress intensity factors. It is also seen that magnitudes of the mode-III stress intensity factors do not vary much along the crack front. Fracture experiments also performed and, using the stress intensity factors from the analyses and crack paths and surfaces are shown. K EYWORDS . Fracture; Mixed Mode; Mode-I/III; Compact Tension Tear; Finite Element Method. I NTRODUCTION ajority of fracture mechanics problems seen in practice are type of mode-I. However, there are still many problems that include mixed mode loading. In that case, mode-I analysis approaches are not sufficient. One of the basic types of mixed mode fracture is mode-I/III, in which both mode-I (opening) and mode-III (tearing) loads act near the crack region. In what follows, a short summary of the studies from the literature related to Mode-I/III is given. H.A Richard et al. investigate 2D - 3D mixed mode crack problems and compared the fracture criteria [1]. They observed that depending on mode-II and mode-III loading more or less crack deflection took place. In experimental part of their study, 3D mixed problems were tested and compared with some criteria, which showed good agreement in terms of twisting angle and kinking angle. Ayatollahi et al. presented a loading fixture for mode-I/III experimental study [2]. Finite element analysis were performed and the results were validated with experimental study using the maximum tangential stress criterion. A code has been developed for fully automatic mixed-mode calculation by Dhondt in 2013 [3]. To verify the code, several specimens were tested and analyzed. Good agreement between analysis and experimental results were shown. In this M