FE-modelling of flexible pipes in aftertreatment system for trucks and buses

Exhaust flexible pipes are components characterised by a complex dynamic behaviour. Friction is generated by internal contacts in the interlock and entails a dynamic softening phenomenon as the excitation amplitude increases. Due to their complex geometry, the modelling is complicated. The purpose of the thesis is to improve the dynamic model by investigating different Finite Element formulations. Shell, connector, and thin-walled pipe elements are implemented in Abaqus, and numerical modal analysis is run. The models are adjusted in order to fit the first two experimental eigenfrequencies identified by running frequency sweeps in shaker tests. Depending on the method, either manual or automatic parametric optimization in Heeds is performed. The results from different models are compared among themselves and in relation to the measurements, and their corresponding pros and cons are stated. Since the pipe elements turn out to be the most efficient and applicable way of modelling for the first case-study of an U-shaped bellow, the method is adopted for other single components and a dual bellow assembly as validation. The model succeeds in fitting the eigenfrequencies for another bellow and its implementation in the complete pipe-assembly allows for coherent results with experimental tests. The match is not reached for a welded flexible hose. New measurements on the shaker table are performed with the aim of capturing the dynamic behaviour of flexible hose, but different results are obtained by using different ways of attaching the accelerometer. The comparison between frequency sweeps at different constant acceleration amplitudes evidences a softening phenomenon due to non-linear behaviour, which strongly affects the response of the component.