عنوان مقاله [English]
In this paper, flexural vibration behavior of functionally graded micro-rotors with a mass eccentricity is investigated on the basis of the modified couple stress theory. The modified couple stress theory is a non-classical one which is capable to take into account the small-scale effects on micro-scale elements and structures with just one higher-order or non-classical material property. It should be noted that it has been experimentally verified that the classical continuum theory fails to properly simulate the mechanical behavior of small-scale flexible structures. The micro-rotor is composed of a flexible shaft and a disk at its middle. Here, the disk is assumed to have a mass eccentricity, which causes forced vibrations. Additionally, the shaft of the micro-rotor is assumed to be made of a functionally graded (FG) material with varying properties in the radial direction. In derivation of the formulation, both gyroscopic effects and rotary inertia are included. By setting the non-classical material property to zero, the formulation is reduced to the classical continuum formulation. Governing equations of motion of the micro-rotor in lateral motions as well as the general form of boundary conditions are derived with the aid of the Hamiltons principle. These equations are transformed into a partial differential equation utilizing complex functions. Next, based on the Galerkin method with two-mode truncation, analytical expressions for vibration characteristics of the micro-rotor, including first two natural requencies in both forward and backward whirl motions, are obtained for the simply-supported cases. Moreover, the amplitude of the forced vibration of the micro-rotor in steady state condition is determined. The forced vibration is due to the mass eccentricity of the disk. With these analytical results in hand, it is an opportunity to evaluate the effect of non-classical material property on the vibrational characteristics of micro-rotors. These non-classical effects have been numerically investigated in an example provided.