Theoretical interpretation of abnormal ultrafine-grained material deformation dynamics

Abstract

Some recent experiments with ultrafine-grained metal samples reveal that it has an abnormal mechanical response on the intensive dynamical loading caused by its impact or electron beam irradiations. On the basis of the original plasticity model, which takes into account dislocation slip and grain boundary sliding, we show that this response is usual for such structure. Moreover, our calculations predict an inverse Hall–Petch relation for ultrafine grained metals at extremely high strain rates (above 107 s−1), while the classical low strain rate experiments and molecular dynamic simulations detects such inverse Hall–Petch relation only for nanocrystalline materials. The main outcomes of present work are the described plasticity model and the conclusions that the ultrafine-grained metals (with grains of about 100–200 nm in diameter) has to have maximal dynamic shear strength and it is the most persistent to dynamic spall fracture because of maximal energy dissipation in it.

Stable microstructure in a nanocrystalline copper–tantalum alloy during shock loading

“…The lack of publications is due to the difficulties in consolidating NC metals because of their poor thermal microstructural stability as well as overall sample dimensions. Consequently, the vast majority of literature has been devoted to computational modeling efforts of simulated microstructures [18][19][20][21][22][23][24][25][26][27][28][29][30][31] . With regard to the limited experimental studies, the work has utilized laser-driven compression of physically deposited thin films or electrodeposits (<500 µm) 32 .…”

Структурно-Временные Особенности Динамического Деформирования Наноструктурированных И Наноразмерных Металлов

“…В работах [11,12] было отмечено, что переход от квазистатического к динамическому режиму деформации металлов осуществляется тогда, когда процесс пластичности начинает определяться не " динамикой" существующих дефектов, а их кинетикой -т. е. скоростью увеличения их объемной доли. В работе [13] Рис. 1.…”