Finite Element Models (FEM) are widely used in order to study and predict the dynamic properties of structures. Comparing dynamic experimental data and analytical results, respectively, of the real and modelled structure, shows that the prediction of the dynamic response can be obtained with much more accuracy in the case of a single component than in the case of assemblies.Generally speaking, as the number of components in the assembly increases the calculation quality declines because the connection mechanisms among components are not represented sufficiently.Specifically for aircrafts, it is quite common that Frequency Response Functions (FRF) obtained via Ground Vibration Test (GVT) show a certain degree of discrepancy from the FRF calculated with the FEM, particularly across the sections where joining is discontinued.When this happens it is necessary to tune up the values of the dynamic parameters of the joints, to allow the numerical FRF to match the results of the experimental FRF. From a modelling and computational point of view, these types of joints can be seen as localized sources of stiffness and damping and can be modelled as lumped spring/damper elements.In this paper this is done by formulating an optimization problem. The approach has been applied to a FEM that mimics the rear fuselage of a commercial aircraft and the numerical results shows that the procedure is very efficient and promising.
The mitigation of the vibrations of components and structures, through the use of rubber mounts, is a common practice in many industries, such as in automotives and aeronautics or energy. It is a very important issue, because it is a key factor not just for the fatigue life but also for matters of comfort. On the other side, these industries make extensive use of finite element models to predict the dynamic behaviour of structures. Therefore, it means that the non-linear constitutive equations of rubber mount devices need to be properly integrated into the global analytical model. The quasi-static and dynamic behaviour of these devices can be quite complex, because they are usually done by a steel cover with an elastomer inside. Experimental test campaigns are usually carried forward to characterize the quasi-static and dynamic behaviour in terms of dynamic stiffness and loss factor. The experiments are designed to determine dependency on the frequency, the dynamic amplitude, the temperature and the preload.In this paper an optimization methodology, combining hyper-elasticity, viscoelasticity and elasto-plasticity constitutive equations will be presented to obtain representative elastomeric behaviour, able to fit the experimental data in hand and to predict the rubber mount behaviour in load conditions different from those tested. The numerical results obtained are in very good agreement with the experimental data.
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