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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reinforced with 0.034 nm thick CNTs. On the other hand, when the thickness of the CNTs increases, it results in an increase in the contact force during the indentation process. This behavior can be attributed to the enhanced stiffness provided by the thicker CNTs, influencing the overall contact behavior of the composite. In Fig. 6(b), the contact force is plotted against the indentation depth for the nanocomposite consisting of FGM and CNTs, with a constant CNTs thickness of 0.102 nm, while varying the elastic gradation parameter (γ e ) as +2, 0, and -2. It is evident that as the gradation parameter increases, the contact force of the CNTs-FGM nanocomposite also increases. The contact area against the indentation depth for different CNTs wall thicknesses (0.034nm, 0.102 nm, 0.170 nm, solid CNT, and FGM) with the gradation parameter taken as constant 2 is plotted in Fig.7.(a). Similarly, Fig.7.(b) presented the effect of the gradation parameter (2, 0 and -2) on the contact area where CNTs wall thickness is constant (0.102 nm).

(a) The correlation between contact area and indentation depth (0.78 nm), with varying CNTs wall thickness (0.034 nm, 0.102 nm, 0.170 nm, solid CNT, and FGM), while keeping the elastic gradation parameter constant.

(b) The relationship between contact area and indentation depth, maintaining a constant CNTs wall thickness of 0.102 nm, while allowing the elastic gradation parameter to vary ( γ e = +2, 0, -2).

Fig. 7 Contact area plots.

Fig.7.(a) presented the contact area verses indetation depth graph with the variation of CNTs wall thickness. It is observed that beyond a specific indentation depth, a noticeable divergence in the deflection of contact area curves becomes apparent. In small indentation depths, the contact area associated with solid CNTs exhibits a higher value, whereas 0.034 nm CNTs yield the smallest contact area. As the indentation depth increases, the difference between the contact areas diminishes, and beyond a certain point, the contact area behavior reverses its nature, as illustrated at smaller indentation depths. For small indentation depths, as CNTs are situated 0.5 nm below the indentation surface, yielding does not commence in thicker CNTs. Instead, yielding occurs in the matrix material in the vicinity of the contact zone, resulting in a higher contact area. Conversely, for thinner CNTs, elastic deformation predominates, leading to a lower contact area. Beyond a specific indentation depth, approximately 0.5 nm into the indentation, yielding initiates in the composite reinforced with thicker CNTs. This yielding leads to a reduction in contact area, subsequently resulting in a higher contact area being observed for the composite reinforced with thinner CNTs. Fig.7.(b) presented the contact area versus indentation depth graph with the variation of material gradation parameters taking the wall thickness of the CNTs constant. As shown in the contact force diagram contact force is higher for the higher value of the gradation parameter, similar pattern is shown in the case of contact area with respect to indentation depth.