Regensburg 2016 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 23: Mechanical Properties II

MM 23.2: Talk

Tuesday, March 8, 2016, 12:00–12:15, H52

Embryonic cracks at grain boundaries in bcc W and Fe: an atomistic study — •Johannes J. Möller and Erik Bitzek — Friedrich-Alexander-Universität Erlangen-Nürnberg, Department of Materials Science and Engineering, Institute I, Erlangen, Germany

Advancing our understanding of grain boundary (GB) fracture is key for a variety of engineering problems spanning from brittle intergranular fracture of polycrystalline components to the failure of micro-electromechanical devices at single GBs. GB cracks are often assumed to be infinitely long and straight. At the very beginning of their existence, however, embryonic cracks are of nano-scale dimensions and have strongly curved crack fronts. Until now, the effect of crack-front curvature on the elementary crack-tip processes has not been studied in detail.

Here, we report on our recent large-scale molecular dynamics simulations of penny-shaped cracks at five GBs in the bcc metals W and Fe. The observed crack-tip processes ranged from purely brittle bond breaking to purely ductile emission of deformation twins. The evolution of crack-tip plasticity is characterized by dislocation emission from growing twins and transmission of the nucleated dislocations through GBs. Our simulations indicate that the initial fracture event at penny-shaped crack fronts can be predicted by analyzing the results for straight cracks. The characteristic crack-tip processes, on the other hand, were not observed in such quasi-2D simulations. This highlights the importance of 3D modeling of cracks to obtain a deeper mechanistic understanding of the ongoing crack-tip processes.