Comparison of beam and plate theories for free vibrations of metal matrix composite pre-twisted blades

Vibration characteristics of pre-twisted metal matrix composite blades are analyzed by using beam and plate theories. A beam element with eight degrees of freedom per node has been developed with torsion-flexure, flexure-flexure and shear-flexure couplings which are encountered in twisted composite beams. In the bean analysis, reduced three-dimensional constitutive relations are used. A triangular plate element presented in the literature is used for the composite material to model the beam as a plate structure. Both the theories have been validated for the isotropic case. This paper summarizes the quantitative comparison of natural frequencies of composite blade obtained by these theories. A parametric study is carried out for both the beam and plate elements results, the parameters being twist angle, fiber orientation, taper ratio and lamination scheme.