PSI - Issue 71

Gnaneshwar Sampathirao et al. / Procedia Structural Integrity 71 (2025) 484–491

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3.1. Effect of Indenter Velocity To understand the influence of indentation velocity on mechanical behaviour, nanoindentation performed on single crystal Al with a (100) orientation, both with and without a 10 Å α -Al 2 O 3 . Fig. 2 shows the hardness values at varying indentation velocities and temperatures. To explain this complexity, it has been examined the underlying dislocation mechanisms. As it is known, under mechanical or thermal loading, crystalline materials undergo elastic and/or plastic deformation. Plasticity often involves the nucleation and movement of dislocations. In our case, a nano-indenter presses into the material, generating a high stress region beneath its tip, prompting the formation and evolution of dislocation networks. As loading continues, dislocations multiply and interact, influencing the measured mechanical properties.

Fig. 2. Evolution of hardness values for Aluminium single crystal indentation on (100) surface

Fig. 3 can be used to understand Fig. 2, illustrates the dislocation structures formed at six indentation velocities (0.1 – 0.6 Å/ps). At lower velocities, dislocations have more time to travel and interact with the boundaries. Since there are using of periodic boundary conditions, dislocations can reflect and accumulate, which lead to higher than usual measured hardness and stiffness etc. Conversely, at higher velocities, the deformation process occurs too quickly where it can be avoided error as obtained at lower velocities. For nanoscratch as seen in Fig. 4, no clear trend with velocity was observed, suggesting that frictional behavior at the nanoscale because of dislocation pileup in our system. F N + F k = 0 … (1) F K = μ K *F N … (2) Where, μ K (friction coefficient) was computed from the F N , F K (Normal and Tangential) forces obtained in our scratch simulations