Small Scale Deformation Study

The understanding of metals and their elasticity has been known for centuries. Experiments, theory and computer modelling gives us easy comprehension of these topics. However this study has aimed to look at the subject in a different way, through the ideas of molecular dynamics. Experiments performed on atomic scales take quite a lot of time and are very costly yet often show very important properties that materials on this scale have. This means that by creating nanoscale simulations researchers can have a better grasp on the mechanics involved in the deformation.

In this study the materials that they were attempting to simulate were that of copper and nickel and how they would react when stress was applied along a singular axis. This is quite practical as copper and nickel have the same crystal structure but the different atomic sizes opens up a challenge for the computer modelling techniques. The simulations of the deformation predict that the structure will slip where the plane is most densely packed however the direction of the extension force relative to the crystal structure should also have an effect. Both the materials demonstrated a much higher yield stress when being compressed than extended and although many of the results between the metals showed similarities there were also quite a few differences. As the “steps” the individual outer atoms are places where stress is likely to concentrate it was believed that defects would naturally congregate here as the temperature was kept low enough that diffusion of defects was minimal. This was true for copper but for nickel the defects remained about ten atomic layers under the surface layer. It was also found that dislocations become rarer and partial dislocations are favoured the smaller the sample of the material. The paper has shown that the intermolecular bonding with the neighbouring atoms combined with their size and the whether the stress was compressive or extensive has a distinct impact on the atomic scale when it comes to the forming and transport of defects along with slip mechanics in general.

Paper links: A comparison of the uniaxial deformation of copper and nickel (1 1 19) surfaces: a molecular dynamics study

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