Joint Identification in Bladed-disks using SEMM and VPT

Bladed disks are fundamental bricks of the rotating parts of a turbomachine, which can include many of them. Although each blade-disk sector can be considered identical, the presence of imperfections or misalignments or inhomogeneity (so-called mistuning) induces high amplification of vibration response. The case of blade-root joints is analysed as a source of mistuning of the contact. The test-case is an academic bladed-disk comprising of 18 blade-root joints. The root has a typical dovetail configuration with two-sided interface per sector. Its relatively long interface (compared to the blade length) makes the joint identification challenging yet interesting. Therefore, some non-classic identification techniques are employed. The joint identification is done by using System Equivalent Model Mixing (SEMM) and Virtual Point Transformation (VPT). The measured dynamics of the internal degrees of freedom (DoFs) are expanded to the interface DoFs by SEMM at the substructure level i.e. the disk and the blade. The substructure SEMM models are transformed to one or more virtual points by interface displacement modes (IDMs). The virtual point IDMs are decoupled from the assembled structure (one blade coupled to the disk at a time) to identify joint parameters. Since each disk and blade interface is considered unique, therefore, the process can be extended to the second blade coupled to the disk (having the first one removed). Such joint characterization is aimed for all the remaining blade to disk interfaces.