Refined structural dynamics model for composite rotor blades

A refined one-dimensional beam formulation based on a mixed approach has be en developed for structural dynamics analyses of rotating and nonrotating c omposite beams and blades of general section shape with open-or closed-sect ion contours. The theory uses a mixed variational approach and accounts for the effects of elastic coupling, shell-wall thickness, warping, warping re straint, and transverse shear deformations. The analysis is validated again st experimental data and other analytical results for composite cantilevere d beams of various cross sections. Good correlation is achieved for all of the cases considered. The influence of mall thickness and transverse shear on the free vibration characteristics of composite beams with either bendin g-torsion or extension-torsion coupling is investigated. For a bending-tors ion coupled beam, the influence of wall thickness becomes important when th e thickness-to-depth ratio of the beam reaches about 30%. The frequency err or in neglecting transverse shear flexibility is about 50% for a bending-to rsion coupled composite box beam with a slenderness ratio of 5.