A new approach to characterizing and modeling the high cycle fatigue properties of cast materials based on self-heating measurements under cyclic loadings

WOSInternational audienceThe present paper proposes, a new model for high cycle fatigue of metallic cast materials (i.e., containing initial casting micro-flaws). This model is developed in a probabilistic two-scale framework taking into account the presence of a population of initial micro-flaws by an indirect approach. The proposed model not only accounts for the failure of samples under high cycle loadings, but also for the thermal effects during cycling in a unified theoretical framework. Thus, an ad hoc identification procedure, essentially based on self-heating tests under cyclic loadings, is proposed. The performance of the proposed model is estimated by comparing experimental and theoretical results in the case of classical fatigue tests on a cast copper-aluminum alloy. The results are very promising

A Probabilistic Multiaxial Two-Scale Model for Cast Materials in High Cycle Fatigue Regime: application to marine propellers

International audienc

A probabilistic multiaxial two-scale model for cast materials in high cycle fatigue regime

International audienc

Identification d’un modèle à deux échelles probabiliste pour la prévision de la tenue à la fatigue polycyclique à partir de mesures d’auto-échauffement sous chargements cycliques

La fatigue polycyclique est un phénomène masqué (la pièce reste élastique). Des approches à deux échelles sont donc développées pour décrire ce phénomène. Une des difficultés majeures de ces approches concernent l’identification du comportement de la phase microscopique. On propose, ici, l’utilisation de la mesure d’auto-échauffement sous chargements cycliques pour, d’une part, identifier ce comportement, et d’autre part, caractériser la population des sites où apparaît la microplasticité

Fast Characterization of High-Cycle Fatigue Properties of a Cast Copper-Aluminium Alloy by Self-Heating Measurements under Cyclic Loadings

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Effet du procédé de compaction isostatique à chaud sur les propriétés à la fatigue polycyclique d'un alliage cupro-aluminium de fonderie

WOSNational audiencePour améliorer la tenue mécanique à la fatigue polycyclique des matériaux de fonderie, la Compaction Isostatique à Chaud (CIC) peut être utilisée. Elle consiste en un traitement thermomécanique des pièces moulées afin de refermer, complètement ou partiellement, les défauts initiaux qu'elles contiennent. On propose ici d'utiliser des mesures d'auto-échauffement sous chargements cycliques et un modèle associé pour caractériser le gain en tenue à la fatigue apporté par le procédé CIC sur un alliage cupro-aluminium de fonderie

Effect of the Thermal History on Macrostructure and Microstructure Development in High-Strength Steel Welds

International audienceThe present work addresses the microstructural and macrostructural development in multipass welded joints. It focuses on multiple thermal cycles induced by successive deposition of welding passes. The local welding-related thermal history was related in detail to the evolution of austenite grains during manufacturing of two high-strength low-alloy steel welds. The analytical Rosenthal thermal model was used to identify the thermal cycles experienced within typical weld metal regions. Selected heat cycles were applied to laboratory specimens, taken from the same weld metal, to investigate microstructural evolution during the welding process. Heat cycle experiments, involving full austenitization, showed the persistence of columnar zones resulting from a memory effect of the prior austenite grains during the reverse transformation. Intercritical heat cycles led to white-etching, softer regions with high fractions of retained austenite. They also showed that the memory of austenite grains was actually stored in elongated retained austenite particles that remained after complete welding. This memory effect vanished under high peak temperatures (typically, 130°C higher than Ac3); this was linked to a competition between growth and merging of elongated, intragranular retained austenite particles, and growth of equiaxed, intergranular austenite particles. Finally, a low peak temperature promoted refined, harder final microstructures

Thermokinetic Modelling of High-Temperature Evolution of Primary Nb(C,N) in Austenite Applied to Recrystallization of 316Nb Austenitic Stainless Steel

International audienceThe size evolution of niobium carbonitrides Nb(C,N) and the evolution of the composition of an austenitic matrix in 316Nb stainless steel were simulated using DICTRA software. For the first time, the complete nine-element composition of steel was taken into account during isothermal and even anisothermal heat treatments. A reduced model was then proposed to optimize the calculation time for complex heat treatments. The change in the mean Nb content in austenite due to Nb(C,N) evolution during different heat treatments was studied. It qualitatively agrees with experimental data as obtained by electron probe microanalysis. Furthermore, the model was successfully applied to explain the effect of heat treatments on the recrystallization behavior of 316Nb steel during hot torsion tests. Moreover, the effect of the thermodynamic database and the number of alloying elements chosen was discussed. We showed that taking into account seven or even nine elements greatly improves the accuracy compared to usual simplified compositions. The proposed method can be useful in designing heat treatments promoting or conversely hindering recrystallization for a wide variety of Nb-bearing steels