Issue 35

G. Kullmer et alii, Frattura ed Integrità Strutturale, 35 (2016) 368-378; DOI: 10.3221/IGF-ESIS.35.42 377 the exit angle is zero. This means that a crack enters a sufficiently compliant inclusion but does not leave it. If Ē is greater than a critical positive value, the exit angle reaches a constant value and the entrance angle is zero. This means that a crack does not enter a sufficiently stiff inclusion. Obviously, both critical values of Ē have the same absolute value and only if Ē is within this range, the crack is able to cross the inclusion. Figure 14 : Comparison of the crack paths through the compliant inclusions with constant orientation angle α = 45° and varying distance from the initial crack. Figure 15 : Transition angles of cracks through inclusions with varying stiffness mismatch (α = 45°, d = 14.7mm) C ONCLUSIONS he results of the presented investigations on the influence of changes in stiffness on the paths of fatigue cracks show, that changes in stiffness cause curved crack paths when they generate an asymmetric stiffness distribution in the neighbourhood of the crack. The deflection of the crack paths and therefore the transition angles at changes in stiffness depend on the stiffness mismatch and the orientation angle between the initial crack and the change in stiffness but they are independent on the distance between the initial crack and the change in stiffness. Only if the magnitude of the stiffness mismatch is less than a critical value the crack is able to cross the change in stiffness. Where the crack crosses the boundary of a change in stiffness the energy release is continuous and the crack path has an inflexion point. R EFERENCES [1] Richard, H. A., Sander, M., Ermüdungsrisse, Vieweg+Teubner Verlag, Wiesbaden, (2009). [2] Fulland M., Risssimulationen in dreidimensionalen Strukturen mit automatischer adaptiver Finite-Elemente- Netzgenerierung, Fortschritt-Bericht VDI, Reihe 18: Mechanik/Bruchmechanik Nr. 280, VDI-Verlag, Düsseldorf, (2003). T