[SY-E13] Symposium E-13

[SY-E13] 3D Aspects of Fracture in Crack - Obstacle Interactions and Effects of Crack Front Curvature

Invited

^○Erik Bitzek¹, Polina Baranova¹, Johannes J. Möller² (1.FAU Erlangen-Nuernberg, Germany, 2.Fraunhofer IWM, Germany)

Traditionally, fracture mechanics mainly considers 2D problems in which the crack front is approximated by a straight line. At the nanoscale, cracks can, however, be strongly curved, e.g., in the case of crack nuclei or as a result of the interaction of a propagating crack with obstacles. Nanoscale crack front curvature can significantly influence the fracture behavior of semi-brittle materials that show a brittle-to-ductile transition with increasing temperature, like refractory metals, intermetallics or semiconductors. Their fracture behavior is ultimately determined by the competition between the dynamics of the atomic bond-breaking processes and dislocation activity in the direct vicinity of the crack. The relative orientation of the local crack front to possible dislocation slip systems can therefore have a major impact on crack tip processes.

Here we present the results of our atomistic simulations of straight cracks in W, Fe and NiAl interacting with various obstacles. Cracks interacting with individual pre-existing lattice dislocations showed stimulated dislocation nucleation and new crack tip blunting mechanisms. Voids were shown to efficiently stop propagating cracks by impeding the re-nucleation of a sharp crack and by facilitating dislocation emission. Fully-3D simulations of penny-shaped cracks revealed an increased tendency for crack tip plasticity compared to straight cracks due to the availability of more slip systems and the resulting dislocation - crack interactions. The results are discussed in the context of the development of predictive multiscale models for fracture toughness.