Vibration Tailoring of Dual-Bonded Sandwich Beams with Nanoengineered CNT-gradated Faces and Micro-Voided Cores

This study presents a comprehensive dynamic analysis of dual-bonded sandwich beams featuring micro-voided cores and nanoengineered carbon nanotube (CNT)-gradated composite faces. The proposed structure departs from conventional sandwich concepts by integrating a quasi-brittle lightweight core whose stiffness and density are modified by uniformly distributed micro-voids with functionally tailored nanoscale reinforcement in the facesheets. The beam is supported by three discrete rows of linear elastic springs to model partial or elastic foundations typically encountered in civil, aerospace, and marine applications. The formulation accounts for the coupled effects of nanoscale gradation, core micro-porosity, and interfacial bonding stiffness, providing a unified framework for vibration tailoring of multilayer composite structures. Five CNT distribution profiles and three volume fractions are examined to reveal how the synergy between material gradation and micro-void effects influences the modal response. Numerical results show that increasing the void index from 0.0 to 0.8 increases the first three natural frequencies by 20–23% due to mass reduction dominance, while enhancing the CNT volume fraction from 0.12 to 0.28 yields up to 30% higher frequencies owing to nanoscale stiffening. The findings introduce a new perspective for designing lightweight and high-stiffness sandwich systems where vibration control and structural integrity are critical, particularly in smart bridges, modular frames, offshore platforms, and blast-resistant panels.