Issue 35

M. Bozkurt et alii, Frattura ed Integrità Strutturale, 35 (2016) 350-359; DOI: 10.3221/IGF-ESIS.35.40 351 study, it was also pointed out that mode-III loads near the crack regions lead to factory-roofing type of ridges and thus friction between the two fracture surfaces. On the other hand Kikuchi et al. investigate of effect on KIII on fatigue crack growth behavior and they showed that crack growth rate near the deepest point of the surface crack decreased [4]. Wei et al. investigated mixed-mode crack growth in ductile sheets experimentally and computationally [5]. Tearing fracture experiments on thin-sheet specimens under combined in-plane and out-of-plane loadings were carried out. To apply load on specimen, they designed an apparatus that allows different loading angles. In this study, systematic finite element analyses of a mode-I/III experimental system are performed. This system is composed of compact tension tearing (CTT) specimen, loading apparatus, bolts and pins. Using the results from analyses of the assembly for different mode-I/III mixity angles and different specimen thicknesses, corresponding fracture analyses are also performed on the specimen submodel and three-dimensional mixed mode stress intensity factors are computed. Fracture experiments are also conducted to check the validity of analysis results. The outline of the paper is as follows: In the next section, details of the finite element models including fracture submodels are given. This is followed by description of the test procedure, the corresponding experimental results and mixed mode fracture criteria comparisons. Finally, conclusions drawn from the studies are presented. F INITE ELEMENT MODELING OF MODE - I / III FRACTURE n this section, details and results of the finite element models are presented. First, finite element models, boundary conditions and loads are described. In the second subsection, results of the finite element models in terms of stress intensity factors are presented. Figure 1 : Finite element model of the mode-I/III fracture test system. Figure 2 : Contact surfaces on the mode-I/III fracture test system. Description of Finite Element Models In Fig.1, overall and exploded views of the solid model for mixed mode-I/III test assembly are shown. Mode-I/III finite element model is shown in Fig. 1. The assembly is similar to that of Wei et al [5], who used thin specimens. In the current study, mode-I / III model is designed for 7 different mixed mode loading angles (0°, 15°, 30°, 45°, 60°, 75° and 90 °). The other difference is that thicker specimens under linear elastic fracture conditions are used, i.e., t =25mm, 20mm, 12.5mm. Loading axis passes through the center of the specimen at any given loading angle. Loading apparatus are connected to the specimen with 8 bolts, 4 bolts for each apparatus. Contacts applied to the mode I/III finite element model are shown in Fig. 2. Bonded always contact type is used between the surfaces under bolt heads and the speciment surfaces, as the bolts are hardly tightened in the experiment. To simulate threaded connections between bolt threads and the matching hole surfaces on the apparatus, bonded always contact type I