Effects of surface curvature and dislocation dynamics

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A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
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Materials Science and Engineering A, Volume 846
The understanding of size effects in micro-crystal plasticity has been in-part based on controlled uniaxial mechanical testing of crystalline micropillars that may be monitored in-situ, using modern microscopy approaches. Nevertheless, it has always been clear that mechanics and materials science are not ideally decoupled in uniaxial micropillar compression, thus agreement between experiments and theory remains challenging. We present a theoretical analysis of the uniaxial compression of micropillars with curved top free surfaces, in consistency with modern experimental thresholds. By using coupled Finite Element and Discrete Dislocation Dynamics simulations we investigate the effect of the small curvature to dislocation microstructure evolution at constant displacement rate. The uniaxial compression of flat micropillars is shown to be consistent with existing literature, with homogeneous stress build up and random activation of sources inside the volume. However, in the presence of a small top-surface micropillar curvature, there are significant dynamical effects on dislocation mechanisms and an overestimate of strain at yielding that leads to large errors on capturing elastic compression moduli and avalanche noise characteristics. Characteristically, for 10 nm-high isotropic curvature, large (>100MPa) stress drops emerge in the average stress, that become larger as the initial dislocation density increases, in direct contrast to expectations and findings for ideally flat micropillars.
| openaire: EC/H2020/857470/EU//NOMATEN Funding Information: We acknowledge support from the European Union Horizon 2020 research and innovation program under grant agreement no. 857470 and from the European Regional Development Fund via the Foundation for Polish Science International Research Agenda PLUS program grant No. MAB PLUS/2018/8. We acknowledge the computational resources provided by the High Performance Cluster at the National Centre for Nuclear Research in Poland.
Dislocation dynamics, Finite element modeling, Plasticity
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Rovaris , F , Papanikolaou , S & Alava , M J 2022 , ' Effects of surface curvature and dislocation dynamics : Dynamical deformation mechanisms for uniaxial compression tests at the nanoscale ' , Materials Science and Engineering A , vol. 846 , 143270 , pp. 1-7 . https://doi.org/10.1016/j.msea.2022.143270