Issue 35

G. Kullmer et alii, Frattura ed Integrità Strutturale, 35 (2016) 368-378; DOI: 10.3221/IGF-ESIS.35.42 370 17 3 32,4 18 39,6 90 86,4 90° 32,4 2 40 5 d A  14,4 line-shaped region with differing stiffness Figure 3 : Geometry of the CT-specimen and positioning of the line-shaped region with differing stiffness. The CT-specimen is partitioned according to Fig. 4. Inside the partitions P1 and P2, the default properties of Young´s modulus and the thickness of the specimen are valid. Whereas inside partition P3, that represents the region with differing stiffness, depending on the type of examination either Young´s modulus or the thickness varies. The partition P2 guarantees a comparable fine mesh in the neighbourhood of the partition P3 and identical boundary conditions independent from the orientation angle α and the distance d of the change in stiffness. Therefore, the border of partition P2 is sufficiently distant from the partition P3 for all investigated orientations and positions of the change in stiffness. Furthermore, Fig. 4 shows the boundary conditions. All simulation models are supported at the positions A, B and C. The bearing is statically determined and symmetrical. The specimen is loaded with distributed line loads of 2500N/mm at the upper and lower inner side of the bore. With a specimen thickness of 5mm the resulting load is 12.5kN. The boundary conditions are chosen in a way that the bearing reactions vanish and a symmetrical deformation of the specimen occurs if all partitions of the specimen have the same Young´s modulus and the same thickness. In this case, a pure mode I-loading is present at the crack tip and the crack should grow straight ahead. Figure 4 : Partitioning of the CT-specimen and definition of the boundary conditions. Fig. 5 shows a typical global mesh exemplary for the CT-specimen with a change in stiffness with an orientation angle α = 45°. The mesh consists of 10-noded quadratic tetrahedral elements. Inside the partitions P2 and P3 where the crack most likely will propagate the edge length of the elements is chosen 1mm whereas in partition P1 an edge length of 2.5mm is sufficient.