Modeling and Optimal Design of Machining-Induced Residual Stresses in Aluminium Alloys Using a Fast Hierarchical Multiobjective Optimization Algorithm

The residual stresses induced during shaping and machining play an important role in determining the integrity and durability of metal components. An important issue of producing safety critical components is to find the machining parameters that create compressive surface stresses or minimise tensile surface stresses. In this paper, a systematic data-driven fuzzy modelling methodology is proposed, which allows constructing transparent fuzzy models considering both accuracy and interpretability attributes of fuzzy systems. The new method employs a hierarchical optimisation structure to improve the modelling efficiency, where two learning mechanisms cooperate together: NSGA-II is used to improve the model’s structure while the gradient descent method is used to optimise the numerical parameters. This hybrid approach is then successfully applied to the problem that concerns the prediction of machining induced residual stresses in aerospace aluminium alloys. Based on the developed reliable prediction models, NSGA-II is further applied to the multi-objective optimal design of aluminium alloys in a ‘reverse-engineering’ fashion. It is revealed that the optimal machining regimes to minimise the residual stress and the machining cost simultaneously can be successfully located

Prédiction des instabilités au cours de l'hydroformage des tubes

Pendant l'hydroformage des tubes, certaines instabilités plastiques peuvent être rencontrées, principalement : la striction, et le flambage. Afin d'éviter ces instabilités, il faut formuler des outils analytiques ou numériques qui permettent leur prédiction. La théorie de la bifurcation du champs de vitesse est souvent utilisée pour la prédiction des instabilités plastiques. A partir de la formulation du problème de bifurcation, on peut développer des outils numériques qui permettent de prédire les instabilités sous un chargement complexe. D'autre part, on peut en déduire des critères analytiques de striction diffuse pour l'hydroformage des tubes longs. Pour certains cas industriels, les critères analytiques simplifiés ne donnent pas des prédictions raisonnables, parce qu'ils ne tiennent pas compte de la non-linéarité géométrique qui accompagne la déformation des tubes pendant l'opération.Pour cette raison, on a développé un critère qui permet de tenir compte de ces changements géométriques afin d'améliorer la prédiction. Ce critère permet de prédire l'éclatement à la suite d'une striction sous un pilotage en pression. De plus, un critère de striction localisé pour les tubes pressurisés a été développé, pour la prédiction des limites de formage dans le cas d'un pilotage en volume. L'étude théorique a été confrontée à des essais expérimentaux réalisés par ARCELOR. La confrontation calculs-expériences a permis une validation des critères, et une explication du phénomène de la localisation des déformations dans les tubes minces pressurisés.During tube hydroforming, necking, bursting, and wrinkling instabilities may occur. For the avoidance of theses failure modes, the bifurcation analysis is often used. In instance, for necking prediction, analytical and simplified criteria could be deduced from the bifurcation formulation for long tubes. But, for some industrial cases, the prediction of critical necking state given by theses criteria is not realistic. This is due to the fact that, theses criteria do not take into account the geomtrical changes of the tube, which are due to the curvature change. For these purpose, a new diffuse necking criteria is proposed including geometric effects in the prediction. on the other hand, for the local necking prediction, the Hill's criterion is not accurate for short tubes, due to the biaxial stretching. As an alternative, a local necking criterion based on a modified Hill's assumption for localized necking is proposed. The numerical calculations carried out for different tube dimensions, explains the geometrical effects on the localization of deformations for pressurized tubes, and improves the accuracy of the proposed criteria. In a collaboration with ARCELOR, the new criteria formulated are compared with experimental cases, and showed a good accuracy.VILLEURBANNE-DOC'INSA LYON (692662301) / SudocSudocFranceF