PSI - Issue 60

Rakesh Bhadra et al. / Procedia Structural Integrity 60 (2024) 149–164 Bhadra et al. / Structural Integrity Procedia 00 (2023) 000 – 000

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(a) (b) Fig.13. Displacement in the y direction of nodes on the line of symmetry for a with indentation depth 0 f 0.78 nm: (a) end of loading stage and (b) end of unloading stage. ( γ e =2, γ e =0, and γ e =-2). In Fig.13., the nodal displacement in the y-direction of nodes located at the top surface of the block or the contact surface is presented at the end of the loading and unloading stages. The variation of CNTs wall thickness and gradation parameter is considered in the analysis. In Fig.13.(a), nodal displacement along the line of indentation or the y- direction is shown, where the CNTs wall thickness is varied while keeping the gradation parameter constant γ e =2. It is observed that the nodal displacement in the y-direction is higher for the lower wall thickness of the CNTs, especially after unloading. This behavior is attributed to the plastic recovery and pile-up phenomenon observed in the indentation of the lower-thickness CNTs reinforced nanocomposite. The pile-up behavior occurs due to plastic deformation taking place in the lower-thickness CNTs, which possess lower stiffness compared to the matrix material. The cylindrical CNTs change from their elliptical shape and attempt to flow the material towards the free portion or just the end of the contracted zone. Overall, the variation in CNTs wall thickness and gradation parameter significantly affects the nodal displacement behavior during the loading and unloading stages, and the observed pile up behavior provides valuable insights into the mechanical response of the nanocomposite under indentation. Fig.13.(b), the nodal displacement in the y-direction of nodes located at the top surface of the block or contact surface is shown with a variation of the gradation parameter (γ e =2, γ e =0, and γ e =-2) while keeping the CNTs wall thickness constant at 0.102 nm. It is evident from the plot that at the end of the loading stage, the nodal displacement in the y-direction is higher for lower values of the gradation parameter. As the gradation parameter decreases, the displacement increases, indicating a stronger response to the applied loading for cases with a lower gradation parameter. However, during the unloading stage, all the lines coincide with each other. This behavior is due to the plastic recovery being different for each case as the gradation parameters vary. The unloading curve does not show significant differences, implying that the unloading response is less affected by the gradation parameter compared to the loading stage. Overall, Fig.10.(b) provides valuable insights into the effect of the gradation parameter on the mechanical response of the nanocomposite during the loading and unloading stages. The variation in the gradation parameter influences the nodal displacement, particularly during the loading stage, while the unloading response shows relatively less sensitivity to the gradation parameter. . 4. Conclusions This study investigates the loading and unloading behavior of CNT-FGM nanocomposites under indentation by a Berkovich indenter. The nanocomposite is made of an elastically graded FGM matrix with CNTs as reinforcement. The inhomogeneity parameter, which determines the degree of grading, varies along the thickness of the nanocomposite block from the contact surface or top surface to the base of the block. A finite element (FE) model was developed in ANSYS using APDL code. To validate the model, the results were compared to two similar