Search

• A new hybrid composite structure containing CNTRC and matrix cracked FRC layers is presented to model damaged blades. • A meshless based computational framework is proposed for nonlinear vibration behaviors of the hybrid composite blade. • The matrix cracks are revealed to have larger effect on the higher order frequency than the first order frequency. • The nonlinear vibration of cracked blade with a larger pretwisted angle is less sensitive to the deflection. A modeling of the large amplitude free vibration of pretwisted hybrid composite blades is studied by considering the laminated structure which is composed of carbon nanotube reinforced composite (CNTRC) layers and matrix cracked fiber reinforced composite (FRC) layers. Two assumptions are made to facilitate this vibration study of hybrid nanocomposite: (1) CNTs are distributed across the layer thickness uniformly or functionally graded, and (2) the parallel slit matrix cracks disperse in the matrix homogeneously. Based on the theory of differential geometry, a novel shell model for pretwisted hybrid nanocomposites blade is developed. The von Kármán strains are adopted to capture the geometrically nonlinear behaviors of blades. The established governing equations are solved accurately and efficiently via the IMLS-Ritz method. The proposed numerical model is verified by making comparison studies and then the influence of crack density, pretwisted angle, CNT distribution and volume fraction, aspect ratio, width-to-thickness ratio, and ply-angle on the large amplitude vibration characteristics of matrix cracked pretwisted hybrid composite blade are scrutinized systematically. The present study serves as a useful benchmark to researchers who intend do further research in this topic. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A comprehensive understanding of the vibration characteristics of rotating blades is critical to avoid resonance fracture. This paper presents the vibration analysis and lay-up optimization of rotating pre-twisted laminated functionally graded CNTs reinforced composite (FG-CNTRC) shallow conical shells. A numerical shallow conical shell model is proposed, and the displacement fields of the shell model are described via the first-order shear deformation theory. Considering the rotating speed, the governing equation of the rotating pre-twisted laminated conical shell is derived, and then solved using the meshless kp-Ritz method. We carry out the comparison studies to demonstrate the accuracy and efficiency of the present model in dealing with the vibrations of this kind of structures. Detailed parametric studies are then performed and demonstrate that the CNT configuration, pre-twisted angle, and stacking sequence play essential roles in vibration behaviors of rotating FG-CNTRC blade. With the nondimensional frequency parameter being the optimization objective function, a genetic algorithm is employed to search for the optimal layering sequence of the rotating shallow conical shells. The optimized results demonstrate that the GA serves as a useful tool for sequence optimization of rotating blade in terms of improving the vibration characteristics. [ABSTRACT FROM AUTHOR]