Development of a test planning methodology for performing experimental model validation of bolted flanges

This work presents a strategy for testing and validating structures connected together with bolted joints, which are the most common components in mechanical structures. Considering the great number of coupled mechanical structures and research studies on this subject, the authors focused this research work on bolted flanges of aircraft engine casings. In fact, the coupling of engine casings is generally obtained by a large number of joints which assure the correct sealing at the flanges' interfaces. From a finite element (FE) modelling perspective, joints are often modelled by either rigid connections or springs, otherwise incurring a very expensive computational time. This modelling approach is not a problem when dealing with low amplitude levels of vibrations. For higher levels of vibrations, joints and flanges cannot be considered rigidly connected and that exerted flexibility at the joints' area can determine nonlinear dynamic behaviour. This work aims to study the dynamic behaviour of bolted flanges by using modal testing performed under controlled response amplitude. Two test structures, (1) a simple bolted flange test case and (2) a sector of a Rolls-Royce aero-engine casing, are tested under high level of vibrations. Both test structures are modelled by FE method, and nonlinear elements are used for modelling the flanges' interfaces so as to perform prediction of nonlinear responses. These predictions are eventually correlated with the measured data.