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Mechanical Failure Mode of Metal Nanowires: Global Deformation versus Local Deformation.

Ho DT, Im Y, Kwon SY, Earmme YY, Kim SY - Sci Rep (2015)

Bottom Line: In addition, there is a competition between global and local deformations.Nanowires loaded at low temperature exhibit global failure mode first and then local deformation follows later.We show that the global deformation originates from the intrinsic instability of the nanowires and that temperature is a main parameter that decides the global or local deformation as the failure mode of nanowires.

View Article: PubMed Central - PubMed

Affiliation: 1] Department of Mechanical Engineering, Ulsan National Institute of Science and Technology, Ulsan 689-798, South Korea [2] Multiscale and Multiphysics Simulation Group and Low-Dimensional Carbon Material Center, Ulsan National Institute of Science and Technology, Ulsan 689-798, South Korea.

ABSTRACT
It is believed that the failure mode of metal nanowires under tensile loading is the result of the nucleation and propagation of dislocations. Such failure modes can be slip, partial slip or twinning and therefore they are regarded as local deformation. Here we provide numerical and theoretical evidences to show that global deformation is another predominant failure mode of nanowires under tensile loading. At the global deformation mode, nanowires fail with a large contraction along a lateral direction and a large expansion along the other lateral direction. In addition, there is a competition between global and local deformations. Nanowires loaded at low temperature exhibit global failure mode first and then local deformation follows later. We show that the global deformation originates from the intrinsic instability of the nanowires and that temperature is a main parameter that decides the global or local deformation as the failure mode of nanowires.

No MeSH data available.


Related in: MedlinePlus

Deformation of the Au [100]/(001) nanowire under tensile loading(a): Snapshots of the nanowire at different strains. (b): Change of nanowire widths in the lateral directions. Bifurcation takes place at a strain of 0.108 and local deformation starts from a strain of 0.114. Cross-section of the nanowire is 3 nm × 3 nm and temperature is 0.01 K.
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f2: Deformation of the Au [100]/(001) nanowire under tensile loading(a): Snapshots of the nanowire at different strains. (b): Change of nanowire widths in the lateral directions. Bifurcation takes place at a strain of 0.108 and local deformation starts from a strain of 0.114. Cross-section of the nanowire is 3 nm × 3 nm and temperature is 0.01 K.

Mentions: We plot the stress and energy curves to strain of a Au (001) nanowire in Fig. 1. The cross-section of the nanowire was 3 nm × 3 nm and the target temperature was 0.01 K. The stress and energy are increasing monotonously as strain increases. The stress reaches the maximum value of 4.4 GPa at a strain of 0.108 as pointed by “A” in Fig. 1a. This value can be regarded as the ideal tensile strength of the nanowire. It is remarkable that the energy is still increasing after the maximum point of stress and there is no visible change near point “A” in the energy curve, as shown in Fig. 1b. Although the stress drops significantly, there is no sudden change in the energy of nanowire. Rather, the strain energy of the nanowire reaches to the maximum value at a strain of 0.113 as pointed by “B” in Fig. 1b, and starts to decrease immediately after point “B”. In Fig. 2a, we present the configurations of the nanowires at some important points that are marked at Fig. 1. From the initial configuration (ε = 0) to the configuration where the stress is the maximum (ε = 0.108), the square nanowire is contracting in both lateral directions (the y- and z-directions) by the same amount, and thus the shape of cross-section maintains square. In many previous reports2262728, the maximum stress has been regarded as the yield stress of the nanowire, because it has been believed that the stress drops due to local failure deformations such as slip, partial slip or twinning that are closely related to the motion of dislocations. However, as shown in the third panel (ε = 0.113) in Fig. 2a, even though the applied strain exceeds the point at which the stress is the maximum, none of such local deformations is observed. Instead, the deformation that makes the drop of stress is a homogenous deformation. Unlike local deformation resulting from the dislocation that initiates at a point and propagates, the homogenous deformation (or the global deformation) takes place in the entire nanowire simultaneously. During this global deformation, sudden expansion in a lateral direction (here in the y-direction) and sudden contraction in the other lateral direction (here in the z-direction) occurs simultaneously. Now, the shape of cross-section is not square but a similar shape of a rectangle. At ε = 0.113, the ratio of a/b becomes 1.1 as shown in Fig. 2a. When we applied further strain, a local deformation was observed (ε = 0.120). The changes in the sizes of nanowire in the lateral directions are shown in Fig. 2b. The thicknesses in both directions were gradually reducing until the stress reached to the maximum and exhibited different changes by a relatively large amount during the stress drop.


Mechanical Failure Mode of Metal Nanowires: Global Deformation versus Local Deformation.

Ho DT, Im Y, Kwon SY, Earmme YY, Kim SY - Sci Rep (2015)

Deformation of the Au [100]/(001) nanowire under tensile loading(a): Snapshots of the nanowire at different strains. (b): Change of nanowire widths in the lateral directions. Bifurcation takes place at a strain of 0.108 and local deformation starts from a strain of 0.114. Cross-section of the nanowire is 3 nm × 3 nm and temperature is 0.01 K.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4471887&req=5

f2: Deformation of the Au [100]/(001) nanowire under tensile loading(a): Snapshots of the nanowire at different strains. (b): Change of nanowire widths in the lateral directions. Bifurcation takes place at a strain of 0.108 and local deformation starts from a strain of 0.114. Cross-section of the nanowire is 3 nm × 3 nm and temperature is 0.01 K.
Mentions: We plot the stress and energy curves to strain of a Au (001) nanowire in Fig. 1. The cross-section of the nanowire was 3 nm × 3 nm and the target temperature was 0.01 K. The stress and energy are increasing monotonously as strain increases. The stress reaches the maximum value of 4.4 GPa at a strain of 0.108 as pointed by “A” in Fig. 1a. This value can be regarded as the ideal tensile strength of the nanowire. It is remarkable that the energy is still increasing after the maximum point of stress and there is no visible change near point “A” in the energy curve, as shown in Fig. 1b. Although the stress drops significantly, there is no sudden change in the energy of nanowire. Rather, the strain energy of the nanowire reaches to the maximum value at a strain of 0.113 as pointed by “B” in Fig. 1b, and starts to decrease immediately after point “B”. In Fig. 2a, we present the configurations of the nanowires at some important points that are marked at Fig. 1. From the initial configuration (ε = 0) to the configuration where the stress is the maximum (ε = 0.108), the square nanowire is contracting in both lateral directions (the y- and z-directions) by the same amount, and thus the shape of cross-section maintains square. In many previous reports2262728, the maximum stress has been regarded as the yield stress of the nanowire, because it has been believed that the stress drops due to local failure deformations such as slip, partial slip or twinning that are closely related to the motion of dislocations. However, as shown in the third panel (ε = 0.113) in Fig. 2a, even though the applied strain exceeds the point at which the stress is the maximum, none of such local deformations is observed. Instead, the deformation that makes the drop of stress is a homogenous deformation. Unlike local deformation resulting from the dislocation that initiates at a point and propagates, the homogenous deformation (or the global deformation) takes place in the entire nanowire simultaneously. During this global deformation, sudden expansion in a lateral direction (here in the y-direction) and sudden contraction in the other lateral direction (here in the z-direction) occurs simultaneously. Now, the shape of cross-section is not square but a similar shape of a rectangle. At ε = 0.113, the ratio of a/b becomes 1.1 as shown in Fig. 2a. When we applied further strain, a local deformation was observed (ε = 0.120). The changes in the sizes of nanowire in the lateral directions are shown in Fig. 2b. The thicknesses in both directions were gradually reducing until the stress reached to the maximum and exhibited different changes by a relatively large amount during the stress drop.

Bottom Line: In addition, there is a competition between global and local deformations.Nanowires loaded at low temperature exhibit global failure mode first and then local deformation follows later.We show that the global deformation originates from the intrinsic instability of the nanowires and that temperature is a main parameter that decides the global or local deformation as the failure mode of nanowires.

View Article: PubMed Central - PubMed

Affiliation: 1] Department of Mechanical Engineering, Ulsan National Institute of Science and Technology, Ulsan 689-798, South Korea [2] Multiscale and Multiphysics Simulation Group and Low-Dimensional Carbon Material Center, Ulsan National Institute of Science and Technology, Ulsan 689-798, South Korea.

ABSTRACT
It is believed that the failure mode of metal nanowires under tensile loading is the result of the nucleation and propagation of dislocations. Such failure modes can be slip, partial slip or twinning and therefore they are regarded as local deformation. Here we provide numerical and theoretical evidences to show that global deformation is another predominant failure mode of nanowires under tensile loading. At the global deformation mode, nanowires fail with a large contraction along a lateral direction and a large expansion along the other lateral direction. In addition, there is a competition between global and local deformations. Nanowires loaded at low temperature exhibit global failure mode first and then local deformation follows later. We show that the global deformation originates from the intrinsic instability of the nanowires and that temperature is a main parameter that decides the global or local deformation as the failure mode of nanowires.

No MeSH data available.


Related in: MedlinePlus