Cracked Blade Detection From Bladed Disk Forced Response

Abstract

The primary task of this study is to offer reliable and accurate model of a bladed disk containing cracked blade. This model allows simulation of bladed disk dynamic behavior for various crack positions and lengths. Due to absence of cyclic symmetry caused by crack presence in the disk, a reduction procedure was implemented to simulate full bladed disk. It is proposed to use crack location as an interface between two substructures for subsequent fixed-interface method application. Harmonic balance method was applied to take into account crack nonlinear behavior under periodically varying loads. The method implementation considers contact interaction between crack sides at the crack being closed. The contact force is calculated using penalty method of contact force calculation. Relative vertical displacements between nodes in contact were used as nonlinear degrees of freedom (DOFs). Developed bladed disk model is able to take into account external excitation forces phase lag caused by difference between number of rotor and stator blades. Also presence of mistuning was considered. It was shown that certain level of mistuning can directly affect cracked blade detectability. Cracked blade dynamic behavior localization plays here very important role. Absence of cracked blade localization results in impossibility to separate cracked blade response at any mistuning level. Validity of zig-zag diagram for structures with disrupted symmetry is shown using developed bladed disk model with presence of certain level of mistuning.