The influence on the coupled vibrations among shaft, disk, and blades of a rotor system due to a cracked blade was investigated analytically. On the shaft-disk-blade system, without a cracked blade, there exist three types of coupled modes, shaft disk blade (SDB), disk blade (DB), and blade-blade. A cracked blade was found to change not only the natural frequencies but also the types of coupled modes. First, the DB modes disappeared and were replaced by SDB modes. Second, in some modes the disk experienced mode localization due to the cracked blade. Numerical results showed that natural frequencies varied with the blade’s crack location and depth. At no bending moment places the crack imposed no effect. The crack affected the natural frequency slightly until its depth reached as deep as 70% then the frequency dropped abruptly.

Issue Section:
Technical Briefs
Keywords:
blades, cracks, discs (structures), rotors, shafts, vibrations, coupled vibration, cracked blade, mode localization, mistuned
Topics:
Blades, Disks, Fracture (Materials), Vibration, Rotors
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 by American Society of Mechanical Engineers
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