Experimental Joint Identification Using System Equivalent Model Mixing in a Bladed Disk

Abstract

<jats:title>Abstract</jats:title> <jats:p>A joint between two components can be seen as a means to transmit dynamic information from one side to the other. To identify the joint, a reverse process called decoupling can be applied. This is not as straightforward as the coupling, especially when the substructures have three-dimensional characteristics, or sensor mounting effects are significant, or the interface degrees-of-freedom (DoF) are inaccessible for response measurement and excitation. Acquiring frequency response functions (FRFs) at the interface DoF, therefore, becomes challenging. Consequently, one has to consider hybrid or expansion methods that can expand the observed dynamics on accessible DoF to inaccessible DoF. In this work, we attempt to identify the joint dynamics using the system equivalent model mixing (SEMM) decoupling method with a virtual point description of the interface. Measurements are made only at the internal DoF of the uncoupled substructures and also of the coupled structure assuming that the joint dynamics are observable in the assembled state. Expanding them to the interface DoF and performing coupling and decoupling operations iteratively, the joint is identified. The substructures under consideration are a disk and blade—an academic test geometry that has a total of 18 blades but only one blade-to-disk joint is considered in this investigation. The joint is a typical dove-tail assembly. The method is shown to identify the joint without any direct interface DoF measurement.</jats:p>

Joint Identification through Hybrid Models Improved by Correlations

“…The disk was not constrained at its centre to avoid errors due to a nonoptimal constraint model [27]. The impact of the constraint model as a possible source of errors on the final results was shown in a previous work by these authors [28]. From these measurements, the accelerance FRFs are collected in Y exp,A and Y exp,B for the blade and disk, respectively.…”

“…In this work, the SEMM method is exploited to generate such a hybrid coupled model Y S,AJB which explicitly contains boundary dynamics. The method was originally proposed in [41] on a numerical test-case and then applied by the authors of the present paper to the real case in [28,42]. The method, which this time uses models generated with the correlated SEMM, is explained here and applied to the blade-disk assembly in Section 8.…”

“…This causes an additional error in the hybrid models. In a recent work of these authors related to the present study on the joint identification [28], the constraint modelling in one of the substructures -the diskproved to greatly affect the the joint identification result.…”

“…In this paper, the new correlated SEMM method is applied for the identification of the same blade-root joint of the bladed-disk tested in Ref. [28]. Both the blade and disk are modelled and tested in free boundary conditions, thereby, minimizing the modelling discrepancies arising from the geometric constraints.…”

Nonlinear substructuring in the modal domain: numerical validation and experimental verification in presence of localized nonlinearities

“…These methods have become very popular since their range of application is very broad: it is possible to obtain the dynamic behavior of complex systems starting from the known dynamic behavior of its component substructures (coupling) [9,10]; on the other hand the behavior of one substructure can be achieved from the known behavior of the complete structure and that of the residual substructures (decoupling) [11][12][13]. It is the case, for example, of the decoupling technique developed by Saeed et al [14] used to identify the linear characteristics of a joint in an assembled structure. Besides, coupling and decoupling can be performed by combining experimental models of some substructures and numerical models of the other substructures [15][16][17], as done when using the Transmission Simulator approach [18].…”