Non-linear ultrasound for characterizing closed cracks in metallic materials

Abstract: The aim of this thesis is to develop a non-destructive testing (NDT) method for detecting and characterizing fatigue cracks in metal components. The first part of these cracks is open, detectable by conventional ultrasonic methods. However, depending on the type of stress to which the mechanical component is subjected, part of the crack may be closed, making it invisible to ultrasound. The consequences of underestimating crack depth can be dramatic, as the service life of mechanical components is greatly reduced. The focus of this thesis is to develop an ultrasonic NDT method for detecting and characterizing the closed part of these cracks.

Cracks in metal parts and their Non-Destructive Testing (NDT) are described, and the impact of crack closure on the performance of different NDT methods is studied. After highlighting the interest of non-linear acoustic methods for the dimensioning of closed cracks, the state of the art of these methods is reviewed. Those with the best sizing capabilities, also considering the possibility of industrialization are then selected for our study. The first selected method known as the "pump wave" method, is used on cracked samples. Its aim is to alternately open and close the cracks using a high-amplitude low-frequency wave. The results are then discussed through analytical modelling of closed crack behaviour. Particular attention is then paid to the method of the "thermal solicitation" of closed cracks, which aims to open through material contraction generated by local cooling of the part to be tested. Its superior crack-opening capability compared to the pump wave, and the various physical phenomena at play during crack opening are studied to characterize this innovative method. The industrialization of the method is then assessed with tests on a real part under industrial experimental conditions.  

Jury :

• Jacques RIVIERE                 Assistant Professor, Pennsylvania State University, USA                       Rapporteur
• Olivier BOU MATAR             Professeur des Universités, Centrale Lille, IEMN                                    Rapporteur
• Andreas SCHUMM               Ingénieur de recherche, EDF                                                                  Examinateur
• Anissa MEZIANE                  Professeure des Universités, Université de Bordeaux, I2M                   Présidente du jury
• Cédric PAYAN                       Professeur des Universités, Aix-Marseille Université, LMA                    Directeur de thèse
• Cécile GUEUDRE                 Maitre de conférences, Aix-Marseille Université, LMA                           Co-directrice de thèse
• Patrick RECOLIN                  Ingénieur de recherche, Naval Group                                                     Membre invité
• Gilles CORNELOUP             Professeur des Universités, Aix-Marseille Université, LMA                    Membre invité

La soutenance de Mr Arthur Perrin est prévue le  jeudi 28 mars à 13h30 à l’IUT d’Aix en Provence dans l’Amphithéâtre Est, 413 Av. Gaston Berger, 13100 Aix-en-Provence