Semnan University Press Mechanics of Advanced Composite Structures 2423-4826 14 1 2027 04 01 Dynamic Analysis of Functionally Graded Nanobeams Using Various Shear Deformation Theories Based on Doublet Mechanics 75 97 10401 10.22075/macs.2026.37204.1823 EN Alireza Javanbakht Department of Mechanical Engineering, Tarbiat Modares University, Tehran, 1464753111, Iran Morteza Karamooz Mahdiabadi Department of Mechanical Engineering, Tarbiat Modares University, Tehran, 1464753111, Iran Journal Article 2025 03 19 This study investigates the vibrational behavior of a functionally graded beam using the doublet mechanics theory. This theory accounts for interactions between constituent atoms within a structure, enabling consideration of atomic-scale structure and orientation relative to the beam axis. While classical Euler–Bernoulli and Timoshenko beam theories are commonly used within the framework of doublet mechanics, they typically neglect key terms associated with shear deformation effects. To overcome this limitation, the present research introduces the novel application of higher-order shear deformation theories (HSDTs) within the doublet mechanics framework. This approach, not previously explored in the literature, provides more accurate predictions of vibrational characteristics. The results reveal that employing doublet mechanics can significantly influence natural frequencies, with deviations of up to 5%. https://macs.semnan.ac.ir/article_10401_c6f8ab8b0d46b157813a42726ca4955d.pdf