Issue 41

T. Vojtek et alii, Frattura ed Integrità Strutturale, 41 (2017) 245-251; DOI: 10.3221/IGF-ESIS.41.33 247 Also, a submodelling procedure was employed to minimize the computational time. The first stage model (global model) described deformation of whole specimen with smooth precrack front (no tortuosity) under respective loads. The second stage model (submodel) contained the tortuous precrack front. Its geometry was parameterized and defined by the main dimensions of the tortuosity (tooth height and length). A zig-zag shape of the precrack front was created by alternating key-points between maximal ( R max ) and minimal ( R min ) precrack front radii and by connecting these points to create the serrated crack front (see Fig. 1). A scripted code ensured that the number of modelled teeth was an integer (to avoid discontinuities at the crack front). Figure 1 : Scheme of the precrack emanating from the notch and possessing a serrated front. Geometrical model was discretized by a very fine mesh of finite elements. ANSYS quadratic elements (SOLID186) were used and the rotational symmetry was employed to create a mostly uniform mesh. The model was adjusted to have 10 elements in the radial direction from the notch tip to the precrack front and 4 elements along each half-tooth at the precrack front. Figure 2 : Submodel (finite element mesh). This arrangement resulted in 9 nodes along each half-tooth. To evaluate the SIFs the ANSYS code used a domain integration around each evaluated point at the precrack front to compute the so-called interaction integral. Then the local SIFs were calculated from this integral [26] with respect to local coordinate systems. This calculation was performed for all nodes along the precrack front which provided 17 values of local SIFs (including one value for the conjoint node) along each precrack tooth. R ESULTS AND DISCUSSION ocal SIFs k 1 , k 2 and k 3 were evaluated for the remote mode III loaded crack with two crack geometries [27]. The first one was a smooth circular crack front and the second one was the serrated front (roughness asperities) characterized by the angle α. The inclination of the crack front segments with respect to the remote shear stress resulted in a non-zero local mode II component. Significance of this component was assessed by the ratio of the local mode II SIF k 2 and the remote mode III SIF K III determined for crack without ledges (asperities). This ratio was denoted r cal and plotted in Fig. 4 for one half of L