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Abnormal stress drop at the yield point of aluminum nanowires: A molecular dynamics study

2011; American Physical Society; Volume: 83; Issue: 16 Linguagem: Inglês

10.1103/physrevb.83.165441

1550-235X

L. Pastor‐Abia, M.J. Caturla, Emilio San‐Fabián, G. Chiappe, E. Louis,

Anodic Oxide Films and Nanostructures

Molecular dynamics (MD) and experimental data indicate that the stress at the yield point of uniaxially stretched nanowires suffers a sudden large drop ($D$). In addition, nanowires show a yield strength (YS) significantly higher than that of bulk material. In this work, aiming to identify the parameters characterizing the nanowire that produce these effects, MD simulations are carried out at low temperature (0.5 K) on defect-free aluminum nanowires stretched along the (100) direction. Nanowires are characterized by the aspect ratio and the average coordination. The results can explain neither the absence of the drop in bulk material nor its much lower YS: both yield strength and drop increase logarithmically with the aspect ratio and linearly as the average coordination tends to its bulk value. Increasing the testing temperature smoothes the stress-strain curve and significantly reduces the YS, but does not eliminate the drop whose relative value $D$/YS remains practically constant. Introducing vacancies reduces both the yield strength and the drop. A detailed analysis of the atomic positions reveals a strong necking at the yield point of defect-free nanowires (absent when vacancies are introduced) that may surely be the cause of the drop.