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) Contact pressure distribution along the contact surface varying CNTs wall thickness (0.034nm, 0.102 nm, 0.170 nm, solid CNT, and FGM) and constant elastic gradation parameter ( γ e = 2).

(b) Contact pressure distribution along the contact surface varying elastic gradation parameter constant ( γ e = 2, 0, - 2) and CNTs wall thickness constant (0.102nm).

Fig.8. Contact pressure plots.

Fig. 8 illustrates the distribution of contact pressure from the indenter's tip to positions away from the tip. Fig.8 (a) shows the contact pressure variation with a constant gradation parameter while varying the CNTs wall thickness, whereas Fig.8.(b) presents the variation of contact pressure for a constant CNTs wall thickness (0.102 nm) and different gradation parameters (γ e = 2, γ e = 0 and γ e =- 2). In Fig.8.(a), it is observed that the contact pressure is higher at the tip of the indenter due to its sharp edge. As one moves away from the tip, the pressure decreases sharply and then gradually diminishes. However, at the end of the contact edge, a slight increment in contact pressure is noticed, which is attributed to the pile-up behavior of the material. For solid CNTs, the contact pressure variation is higher, while for CNTs with a wall thickness of 0.034 nm, the contact pressure is lower. The decrease in contact pressure with decreasing CNTs wall thickness is important since it falls below the value of the functionally graded material (FGM). This occurs because lower wall thickness results in lower stiffness, even lower than that of the matrix material of FGM. The pressure distribution along the contact surface appears smooth for the functionally graded material (FGM) only. In contrast, for the nanocomposite, ups and downs are observed due to the presence of CNTs in various places, creating resistive forces against deformation. Moving on to Fig. 8(b), it becomes evident that the contact pressure distribution is influenced by the gradation parameters, following a similar pattern to the distribution of contact force and contact area. The gradation parameters play a crucial role in formative the contact pressure distribution across the contact surface. 3.3.1 Analysis of stresses In this section, the von Mises stress distribution over the nanocomposite is analyzed at the end of both the loading and unloading stages. The results are presented and discussed to understand the stress patterns. End of the loading and unloading stages, it is observed that the von Mises stress generated in the CNTs near the contact zone is significantly higher in amplitude compared to that in the matrix material. To provide a clearer understanding, two contour plots are presented (mainly affected region is presented):  The first plot shows the stress distribution for the entire nanocomposite (combining both CNTs and FGM) marked by (i),  The second plot shows the stress distribution for only the FGM in the nanocomposite marked by (ii). By comparing these two contour plots, the stress concentration and distribution patterns can be better comprehended, leading to insightful discussions and conclusions about the mechanical behavior of the nanocomposite during loading and unloading.