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Modélisation du comportement cyclique et de la durée de vie d'aciers à outils martensitiques

Vincent Velay 
Abstract : This work is a contribution to the description of the behavior and the assessment of the fatigue life of hot work tool steels.For that purpose, a methodology was implemented involving two complementary parts that are the investigation of behaviorand lifetime models adapted to tempered martensitic steels. The cyclic behavior of X38CrMoV5 (47HCR) and 55NiCrMoV7 (42HCR) steels was studied under various load and temperature conditions. The influence of the strain rate and strain amplitude, of the dwell times within cycles as well as ratcheting or plastic accommodation effects for stress controlled tests, were taken into account in the modeling. Two models (ONERA, 2M1C) formulated in the framework of the irreversible processes of thermodynamics were considered. After their presentation, they were identified successfully by complexity level growing, according to the kind of loads taken into account. Compared with ONERA model, 2M1C model allows a better description both of strain controlled and stress controlled stress tests. Moreover, the two different mechanisms included in the model were related to the microstructural evolutions (dislocations and carbides) identified in low cycle fatigue. Two validations were performed providing interesting results: the first one, in an isothermal case, performed on different notched specimens under displacement controlled tests, the second one, in a non-isothermal case, related to thermal fatigue tests carried out in a co-operative project with the KARLSTAD university (Sweden). Fatigue life investigation of X38CrMoV5 steel was addressed in a second part. In order to cover the loading conditions of the hot forming processes, LCF tests were carried out to complete an existing database. The initiation and propagation mechanisms induced by fatigue relaxation test at the temperature of 560°C were investigaded. A non isothermal continuum damage model (ONERA) was identified. Analysis of experimental results do not reveal time dependant damage mechanisms, so only a fatigue damage component was activated in the model. The last part of this work relates to the lifetime model validation. The predictions provided by the model were compared with the number of cycles to failure resulting from LCF and TMF tests obtained in a previous work.
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Submitted on : Tuesday, April 26, 2005 - 8:00:00 AM
Last modification on : Thursday, March 12, 2020 - 1:30:13 PM
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  • HAL Id : pastel-00001209, version 1



Vincent Velay. Modélisation du comportement cyclique et de la durée de vie d'aciers à outils martensitiques. Engineering Sciences [physics]. École Nationale Supérieure des Mines de Paris, 2003. English. ⟨pastel-00001209⟩



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