Verification, validation and variability for the vibration study of a car windscreen modeled by finite elements

The main purpose of this paper is to investigate verification, validation and variability issues applied to an industrial component: a car windscreen. The windscreen is a sandwich structure whose stacking sequence contains five layers. The two external thick layers are made of glass, while the three thin intermediate layers are made of appropriate polymers. In this framework, two main objectives are identified for this paper. The paper focuses the attention on the study of the dynamics of an acoustic windscreen under free-free and real boundary conditions. An application of the verification and validation methodology is presented to assess the capability of finite element models to predict the natural frequencies of the acoustic windscreen, in presence of intra variability due to temperature variation. Indeed, intra variability of glue and polymers' elastic properties leads to intra variability of the dynamic behaviour of the windscreen. Experimental campaigns, in free-free and real boundary conditions, have been performed in a climatic chamber. The effect of the temperature changes on the windscreen vibration behaviour has been evaluated and the component experimental intra variability estimated. A numerical study has been performed as well. Three different numerical models have been considered: a simplified model in free or clamped conditions, a trimmed body model. The verification stage, including convergence studies, concludes that the multilayer shell model approach is valid at low temperature, when polymers are relatively stiff. On the contrary, at higher temperature, polymers are very flexible and shell models lead to significant errors due to considerable transverse shear effects. Finally, the main result is that a solid model must be used for the windscreen to correctly reproduce the physics at different temperatures. A validation stage, involving numerical and experimental results, has been performed to evaluate the predictive capability of the developed numerical models. Validation metrics, which assess the mean value and the variability level of the frequencies, are proposed. The finite element models lead to very satisfactory results for the mean values of the frequencies. The general trends of the experimentally observed intra variability are also well reproduced. Nevertheless, further investigations are necessary to improve the predictive capability of the numerical model that currently underestimates the experimental intra variability. This discrepancy is essentially due to the complex non-linear behaviour of polymers.