SIZE-DEPENDENT VIBRATION ANALYSIS OF MULTILAYER COMPOSITE MICROBEAM BASED ON NEW MODIFIED COUPLE STRESS THEORY

A refined higher-order zig-zag model in conjunction with a new modified couple stress theory capable of capturing scale effect is proposed for vibration analysis of composite microbeams. The aim is mainly focused on the effects of transverse shear stresses on the accurate prediction of natural frequencies for composite microbeams. Differing from previous work, transverse shear stress satisfies the interlaminar continuity condition, whereas the higher-order derivatives of displacement variables have been eliminated by employing the three-field Hu-Washizu (HW) mixed variational principle. Moreover, accurate transverse shear stresses are introduced in motion equations by using Hamilton's principle, which can actively impact the accurate prediction of natural frequencies of composite microbeams. Within the framework of the variational formulation, the governing equation and corresponding boundary conditions can be obtained. The performance of the proposed model is tested by analyzing vibration behaviors of the simply supported multilayered composite microbeams. The effects of the material length scale parameters, the material constants, and layouts on the natural frequencies of the composite microbeam are completely investigated. The results show that the proposed model can accurately predict the scale effect of composite microbeams, whereas the models violating the continuity conditions of transverse shear stresses largely overestimate the natural frequencies of composite microbeams.