Dresden 2014 – wissenschaftliches Programm

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MM: Fachverband Metall- und Materialphysik

MM 22: Mechanical properties I - Plastic deformation & fracture

MM 22.4: Vortrag

Dienstag, 1. April 2014, 11:00–11:15, IFW B

Ab-initio modelling of mode I cleavage — •Beatrix A. M. Elsner and Stefan Müller — Hamburg University of Technology, Institute of Advanced Ceramics, Denickestr. 15, D-21073 HH

In this contribution we focus on the atomistic modelling of fracture, employing density functional theory to investigate the response of Cu and TiO₂ to mode I loading. As long as structural relaxations are omitted, the universal binding energy relation [1] may be applied to obtain the theoretical strength. However, relaxations can significantly affect the cleavage energy, and the stresses due to rigid displacement can only be considered an upper limit. If atomic relaxations are allowed, cleavage is treated as an energy minimization problem, and rupture will occur at the critical displacement l_c for which the Griffith criterion is fulfilled: E_strain(l_c)=E_cleavage(l_c). As the strain energy depends on the system dimension perpendicular to the cleavage plane, the critical displacement is proportional to the square root of this system dimension. A consequence of this size effect are unphysical results in the limit of large system dimensions. We have used the nudged elastic band method (NEB) to study the transition from strain to cleavage, and we find that the energy barriers involved in the transition increase with increasing system size. This opposes the above-mentioned size effect and may limit the critical displacement. Further, our calculations suggest that prior to surface separation, the strain will localize close to the cleavage surfaces.
Supported by DFG, SFB 986, project B3.
J. H. Rose, J. R. Smith, J. Ferrante, Phys. Rev. B 28, 1835 (1983).