Thermal fatigue, a useful tool to assess low cycle fatigue damage in superalloys for components experiencing thermal transients

International audienc

La fatigue sous chargements thermiques et mécaniques combinés

42e Colloque de Métallurgie de l'INSTN Matériaux pour les machines thermiquesInternational audienceOn examine le problème de la fatigue sous chargements thermiques et mécaniques des superalliages utilisés dans les turbines à gaz notamment aéronautiques. La simulation en laboratoire nécessite d'utiliser conjointement des essais de fatigue thermique sur des structures simples et des essais de fatigue anisotherme sur des éléments de volume. La modélisation est nécessaire pour extrapoler les résultats aux conditions de service. Les équations basées sur une théorie viscoplastique unifiée à variables internes permettent de décrire le comportement en fatigue anisotherme. Les conditions sévères en aéronautique impliquent souvent de considérer l'intexaction entre l'oxydation, le fluage et la fatigue. On dispose de modèles d'endommagement dont la capacité de prévision devient satisfaisante

L’autogestion en couleur. L’expérimentation électorale des listes alternatives

Erörterung der letzten Wahlsiege der grünen (Oekologisten) und bunten (Frauen, Homosexuellengruppen, Bürgerinitiativen...) Listen. Sind sie dazu geeignet, den Durchbruch der Selbstverwaltung in die politische Sphäre zu ermöglichen ? Diese Problematik wird anhand von zwei Texten dokumentiert.A study of the recent success of “green” (ecology) and multicolored (women’s gay rights, and self-help groups) candidates. Do they represent a breakthrough in political self-management ? Two documents are presented to study this question.Chataigner Alain, Maudet Pierre, Crips Liliane, Gabriel Nicole. L’autogestion en couleur. L’expérimentation électorale des listes alternatives . In: Autogestions, NS N°2-3, 1980. Mouvements alternatifs et cogestions en Allemagne fédérale. pp. 277-287

Incremental modeling of relaxation of prestressing wires under variable loading and temperature

International audienceThis paper presents a model of prestressing steel relaxation under various levels of loading and temperature. This incremental model enables the delayed strain of prestressing steel wires to be calculated and takes the non-linear coupling of temperature and loading effects into account. It considers different experimental results that could occur in nuclear containment structures, for which a temperature up to 140 °C could be reached for prestressing wires should a loss-of-coolant accident occur. The constitutive law for prestressing steel relaxation is presented, followed by an illustration of the numerical implementation of the proposed model. Finally, the model responses are confronted with experimental results available in the literature supplied by Toumi Ajimi et al. (2017) for the thermo-mechanical conditions between 20 and 140 °C in terms of temperature and 70%–80% of loading ratio

Laminated materials with plastic interfaces: modelling and calculation

International audienceIn this paper, a model of laminated plates called M4-5N and validated in a previous paper is modified in order to take into account interlaminar plasticity by means of displacement discontinuities at the interfaces. These discontinuities are calculated by adapting a 3D plasticity model. In order to compute the model, a Newton–Raphson-like method is employed. In this method, two sub-problems are considered: one is linear and the other is non-linear. In the linear problem the non-linear equations of the model are linearized and the calculations are performed by making use of a finite element software. By iterating the resolution of each sub-problem, one obtains after convergence the solution of the global problem. The model is then applied to the problem of a double lap, adhesively bonded joint subjected to a tensile load. The adhesive layer is modeled by an elastic–plastic interface. The results of the M4-5N model are compared with those of a commercial finite element software. A good agreement between the two computation techniques is obtained and validates the non-linear calculations proposed in this paper. Finally, the numerical tool and a delamination criterion are applied to predict delamination onset in composite laminates