Vibrational analysis of nanocomposites under hygrothermal effect

Abstract

This thesis focuses on the analysis of free vibrations in laminated composite plates with a polymer matrix reinforced by carbon nanotubes (CNTs), distributed either uniformly or in a functionally graded manner. The primary objective is to develop lightweight, stiff, and multifunctional composite structures capable of operating efficiently under hygrothermal environmental conditions.The CNTs are incorporated according to various functionally graded distribution patterns (UD, FG-X, FG-O, FG-A), enabling controlled variation of mechanical properties through the plate thickness. The effective material properties are estimated using the rule of mixtures, accounting for hygrothermal effects on both the polymer matrix and the reinforcements. The modeling approach is based on the First-Order Shear Deformation Theory (FSDT), which is well-suited for the analysis of laminated plates. The equations of motion are derived using Lagrange’s principle, and hygrothermal effects are introduced through thermoelastic coefficients in the constitutive model. The finite element method is employed to model the vibrational response of the plate under various boundary conditions. The influence of several parameters is investigated, including plate geometry, stacking sequence, CNT volume fraction, distribution pattern, and hygrothermal conditions. The numerical results are validated through comparison with existing literature and demonstrate that functionally graded CNT distributions enhance the effective stiffness and optimize the vibrational performance of the structures. In particular, certain non-uniform distributions achieve a better performance under hygrothermal loading. This study provides valuable guidelines for the optimized design of CNT-reinforced nanocomposite structures, suitable for high-performance applications in fields such as aerospace, automotive engineering, and smart structures.