Cracking-induced mistuning in bladed disks

A study of the mechanisms of cracking-induced mistuning in bladed disks is presented in this paper. An analytical model for a bladed disk was formulated using lumped-mass beams, and a cracked blade was represented by a beam with a through crack at the root. Local stiffness reduction due to cracking was incorporated using a flexibility matrix method. The dynamic characteristics of the bladed disk were analyzed for the tuned system and then for the mistuned system with cracks of various depths introduced at the root of a blade. The dynamic characteristics of the mistuned system with a cracked blade were evaluated and the mistuning pattern due to blade cracking was investigated. The mechanisms of cracking-induced mistuning were elucidated by analyzing the mode localizations and the reductions in natural frequency for different coupling ratios between the disk and blades. The results show that the occurrence of a cracked blade significantly increases the response amplitude of the other uncracked blades and therefore gives rise to high cycle fatigue damage. In the present study, the relationship between the cracked blade and its vibration response signature is established, hence providing the essential guidance required for blade crack detection procedures and for blade failure investigations.