Etude expérimentale et modélisaton de la micro-propagation à partir d'anomalies de surface dans l'Inconel 718DA

Abstract : Aircraft engine manufacturers have to meet with new certification requirements in damage tolerance. In particular they have to demonstrate that the presence of small surface anomalies introduced on engine parts during maintenance operations in critical areas do not lead to failure during service life. This study was undertaken to characterize the harmfulness of scratch and dent type surface anomalies on the fatigue life of the Nickel based superalloy Direct Aged Inconel 718.The influence of maximal stress, temperature, type and depth of surface anomalies was evaluated in a large series of experiments. An experimental and numerical in-depth study of the potential drop technique led to a good control of this tool and allowed to efficiently detect crack initiation and to measure the crack propagation. Indeed, the use of this technique has revealed that the crack initiation from scratches and dents is very rapid but that the first stages of crack growth are delayed.Specific tests were then performed to identify the physical origin of the observed phenomenon. A heat treatment was used to show that the compressive residual stresses created during the introduction process of surface anomalies have a great influence on the fatigue life. Different experimental and numerical techniques were used to quantify these residual stresses and some directions were identified to establish a new model able to predict the fatigue life of scratch and dent type surface anomalies.
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Luc Doremus. Etude expérimentale et modélisaton de la micro-propagation à partir d'anomalies de surface dans l'Inconel 718DA. Autre. ISAE-ENSMA Ecole Nationale Supérieure de Mécanique et d'Aérotechique - Poitiers, 2014. Français. ⟨NNT : 2014ESMA0003⟩. ⟨tel-01495450⟩

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