Blade tip characteristics of turbine disks with cracks

Crack detection of turbine disks is of great significance in aero-engine health monitoring. The traditional non-destructive testing (NDT) methods are not applicable for in-situ or online monitoring of crack propagation. In order to monitor the crack propagation via measured signals, it is necessary to investigate the dynamic characteristics of cracked turbine disks first. In this paper, finite element analysis (FEA) is carried out to study the blade tip characteristics of turbine disks with different types and size of cracks. Three observation parameters, i.e., blade tip clearance change, blade spacing and blade twist angle, are proposed as crack indicators. The effects of different crack types (e.g., circumferential crack, radial crack, crack at the center hole and crack at the bottom of the mortise) on the observation parameters are discussed qualitatively. Then the circumferential crack is selected as an example for the quantitative analysis. The circumferential cracks with different length, width, location and number are studied and compared systematically. The qualitative analysis results show that the three observation parameters can be used to detect different crack types except the crack at the center hole. The quantitative analysis results show that blade spacing is most sensitive to size parameters without crack width. The conclusions can provide proofs for the blade tip timing (BTT) of cracked turbine disks.