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MM: Fachverband Metall- und Materialphysik

MM 36: Topical Session (Symposium MM): Fundamentals of Fracture

MM 36.3: Talk

Wednesday, March 14, 2018, 12:15–12:30, TC 006

T-stress and the brittle-ductile behavior of edge cracks in 3D iron crystals — Anna Machová, •Radek Kolman, Alena Uhnáková, and Petr Hora — Institute of Thermomechanics, v.v.i., CAS, Dolejskova 5, 18200 Prague 8, Czech Republic

According to continuum treatment, the sign of T-stress in SEN specimens loaded uni-axially in mode I depends on boundary conditions and sample geometry. Since the sign of the T-stress can change theoretically brittle vs. ductile behavior of cracks, we verified recently the continuum predictions via molecular dynamic simulations (MD) in 3D bcc iron atomistic samples of SEN type. Crack orientation is (-110)[110] (crack plane/crack front), the axis of potential crack extension corresponds to [001] direction.

Under boundary conditions corresponding to constant stress at the borders the T-stress sign is negative for a short edge. For a relatively long crack it is positive. At higher level of linear loading, dislocation emission on <111>{112} slip systems was detected at the short crack with negative T-stress, while cleavage or brittle fracture was detected at the long crack with positive T-stress under relatively slow loading rates.

Behavior of relatively long cracks has been studied under constant displacement conditions, where negative T-stress is predicted. MD stress calculations confirm the change of the T-stress sign with the change of boundary conditions. Under higher loading, dislocation emission on <111>{112} slip systems and crack blunting were detected.

Acknowledgements to GACR 17-12925S.