Vibration characteristics of matrix cracked pretwisted hybrid composite blades containing CNTRC layers

Stiffness degradation due to matrix cracks is the main initial form of damage in composite laminates. Moreover, the vibration characteristics may change due to the degradation of blade stiffness caused by the introduction of matrix cracks. This paper presents a solution method for studying the static free vibration behaviors of pretwisted hybrid composite blade containing carbon nanotube reinforced composite (CNTRC) layers as well as matrix cracked fiber reinforced composite (FRC) layers. Two types of structure, namely Structure-I and Structure-II, are investigated. The CNTRC layers in Structure-I are considered with carbon nanotubes (CNTs) arranged in uniformly distributions, while Structure-II arranged in functionally graded distributions. The degraded stiffness of cracked layers is modeled via the self-consistent model (SCM) micromechanical framework. A shell model for pretwisted blade is proposed based on the theroy of differential geometry. To consider the effect of the transverse shear deformation and rotary inertia on the vibration behaviors,the first order shear deformation theory (FSDT) is adopted in describing the kinematics of blade. The improved moving least-squares Ritz (IMLS-Ritz) method is engaged to discretize the partial differential equations over the computational domain. Comparison studies indicate that the proposed predictive model can furnish very accurate results for pretwisted blades. Parametric studies on the effect of CNT distribution configuration, matrix crack density, aspect ratio, width-to-thickness ratio, twisted angle, as well as ply-angle on the vibration characteristics are revealed.