A stepwise approach for fatigue evaluation of engine accessories prior to prototyping using hybrid modelling technology

To improve the prediction of fatigue performance of automotive components in their early design stage, the operational boundary conditions and loads have to be modelled. The use of an experimental description of the dynamic behaviour of existing parts of the final assembly is proposed. 3 different methods to couple these measured data to the design FE model are presented. The first method aims at direct application of frequency dependent boundary conditions to the free-free FE-model. Next, the coupling of a FE-modal model of the component to the experimental modal model of its carrying structure is discussed. The third method uses impedance coupling algorithms to predict transferfunction matrices after assembly starting from FE-calculated interface FRF of the compoment and measured interface FRF on the carrying structure. The methods are applied to estimate resonance frequencies of a newly designed alternator support when bolted to a truck engine. Experimental evaluation data are measured on a prototype support. To minimize bias errors, the original FE-model is correlated and tuned prior to the application of coupling algorithms, based on experimental modal analysis on the prototype component.