Study on the Vibration Characteristics of Composite Rotor Blades in Humid Environment

During the operation of helicopters, composite rotor blades commonly experience hygroscopic weight gain and degradation of material properties, which in turn affects the vibration characteristics of the rotor system. Nevertheless, research in this area remains insufficient. To investigate the impact of moisture absorption on the vibration characteristics of composite rotor blades, this paper employed the finite element method (FEM) to establish a hygroscopic model and a dynamic model of the rotor blade. The study analyzed the mass characteristics, sectional stiffness characteristics, and vibration characteristics of composite rotor blades after saturated moisture absorption. The results indicate that in wet environments, moisture absorption primarily influences the mass properties of the blade in the airfoil segment. Additionally, a higher area percentage of PMI Foam in the blade's cross‐section correlates with a higher saturated moisture absorption rate. After saturated moisture absorption, the blade's sectional stiffness exhibits a significant decline, with reductions reaching 20%–30%. Meanwhile, the blade's natural frequency also decreases. Upon examination of the Campbell diagram of the rotor blade, it can be concluded that humid environments adversely affect the vibration characteristics of helicopters. This paper can provide a reference for helicopter composite blade design, and due to the complex state changes during the actual helicopter service, further research is needed to improve the engineering value of this research.