Prise en compte des contraintes résiduelles de traitement thermique dans la prédiction de la tenue en service des culasses en aluminium

This paper deals with the computational modeling of the high cycle fatigue of the aluminum cylinder head (HDI diesel engine). Before being shrinked on, fixed onto the engine block and used, these components are submitted to a thermal treatment (quenching and ageing) to improve their mechanical properties. This gives rise to large residual stresses during quenching and therefore its modeling becomes necessary in order to obtain accurate numerical prediction. A series of tests was carried out at the PSA Peugeot Citroën production line from which the experimental cooling curves were determined. The experimental data were fitted with a simple analytical function H = f(T_wall). Then, once the parameter identification was achieved, the remaining residual stresses followed from a simple mechanical analysis. It was found that the stresses in the local cracking failure area are tensile and therefore strongly unfavorable for the high-cycle fatigue endurance in the case of water quenching. In addition, the account of the residual stresses in the fatigue dimensioning, at the end of the thermal treatment, leads to predictions for the risk regions which are consistent with the experimental observations.