Thesis defenses

David Melle 

Thesis in partnership with SAFRAN on "the effect of chemical finishing on the fatigue resistance of titanium alloys."

Summary 

The powder bed laser melting process is a highly popular additive manufacturing process, but one that produces surface conditions that are detrimental to the performance of parts under repeated stress. In order to improve mechanical strength, particularly in terms of fatigue, surface finishing treatments are being developed. The objective of this thesis is to study the fatigue resistance of parts produced by laser powder bed fusion and to evaluate how this resistance evolves as the surfaces are finished. A model that takes into account all the influencing factors is also proposed. The influence of the material's microstructure on performance in the presence of surface irregularities is discussed at length.

Composition of the jury

• Philippe BOCHERUniversity Professor, School of Advanced Technology (Rapporteur)
• Yves NADOTUniversity Professor, Pprime Institute, ISAE-ENSMA (Rapporteur)
• Myriam BROCHUUniversity Professor, Polytechnique Montréal (Examiner)
• Pascal LAHEURTEUniversity Professor, LEM3, University of Lorraine (Examiner)
• Franck MORELUniversity Professor, LAMPA, Arts & Métiers (Examiner)
• Étienne PESSARDSenior Lecturer, LAMPA, Arts & Métiers (Examiner)
• Daniel BELLETTResearch Engineer, LAMPA, Arts & Métiers (Examiner)
• René BILLARDON Engineer, Safran Fellow (Examiner)
• Martine MONIN Engineer, Safran (Guest)

Thesis supervised by Étienne PESSARD and Franck MOREL and co-supervised by Daniel BELLETT
Industrial supervision: René BILLARDON and Martine MONIN

Practical information

Location: Arts et Métiers Campus Arts et Métiers
Date: December 7, 2023
Time: 2:00 p.m.

Madyen Nouri 

Thesis completed with the ESI Chair on "artificial intelligence combined with physical and hybrid models for simulating casting defects."

Summary 

In industrial environments, several material forming techniques are used. Casting is a widely used process for forming materials, allowing the required shape to be produced with less raw material consumption. It can be used to form various metals such as aluminum alloys. However, various defects can appear in the resulting part, contributing to crack initiation and reduced fatigue strength, such as solidification shrinkage defects. This fact highlights the importance of studying the presence of these defects in the final part. Although numerical simulation and experimental approaches play a major role in designing processes to circumvent these anomalies, this requires several simulation iterations with a particular set of parameters to achieve an optimized process configuration. In this work, artificial intelligence-based methods are proposed to learn from limited simulation data and generate efficient real-time simulation results. These models can be enriched with experimental data to develop hybrid twins that predict and correct the discrepancy between experimental and simulation results. The effectiveness of the proposed methodologies is evaluated on various case studies. These solutions can help open up prospects for more data-driven solutions, reducing the time cost in the design phase.

Composition of the jury

• Antonio Falco: University Professor, CEU Cardenal Herrera University (Rapporteur)
• Rudy Valette: University professor, CEMEF, Mines Paris (Rapporteur)
• Jean-Yves Hasco: University professor, GeM, Ecole Centrale de Nantes, (Examiner)
• Marianne BERINGHIER: Senior Lecturer, ISAE-ENSMA, University of Poitiers, (Examiner)
• Francisco CHINESTA: University Professor, PIMM, Arts et Métiers(Examiner)
• Amine AMMAR: University Professor, LAMPA, Arts et Métiers(Examiner)
• Aude CAILLAUD: Associate Professor, LAMPA, Arts et Métiers(Examiner)
• Julien ARTOZOUL: Associate Professor, LAMPA, Arts et Métiers(Examiner)

Thesis supervised by Mr. Amine AMMAR and co-supervised by Mr. Julien ARTOZUL, Ms. Aude CAILLAUD, and Mr. Francisco CHINESTA

Practical information

Location: Arts et Métiers Campus Arts et Métiers
Date: December 11, 2023
Time: 9:30 a.m.

Thomas Landron

Thesis conducted with STELLANTIS on "the effect of porosity on the fatigue resistance of die-cast aluminum alloys."

Summary 

This thesis explores the influence of porosity and stress gradients on the fatigue behavior at high cycle fatigue (HCF) of the AlSi9Cu3 alloy used in the automotive industry. Defects, such as gas pores and oxide veils, exhibit a heterogeneous distribution with complex porosity networks. A testing methodology, using test specimens of different thicknesses from the same raw sample, is developed to study these gradients. The results show that the interaction between porosity and stress gradients controls fatigue behavior, influencing initiation, the nature of critical defects, and strength levels. The effect of defects is analyzed using a Kitagawa-Takahashi diagram approach and stress intensity factor threshold (∆Kth). Fatigue resistance is related to defect size, characterizing short and long crack behavior. The interactions between fatigue cracks and defects are studied in situ, revealing significant crack accelerations, considerably reducing fatigue life. A model of propagation in FGNC is proposed, highlighting the need to take into account an initiation phase and the complexity of damage mechanisms in porosity network-type defects.

Composition of the jury

• Mr. Jean-Yves BUFFIERE, University Professor, MATEIS, INSA Lyon (Rapporteur)
• Mr. Fabien SZMYTKA, Associate Professor, ENSTA Paris, Institut Polytechnique de Paris (Rapporteur)
• Ms. Nathalie LIMODIN, Director of Research, CNRS, Ecole Centrale de Lille (Examiner)
• Mr. Luc REMY, University Professor, Materials Center, École des Mines de Paris (Examiner)
• Mr. Franck MOREL, University Professor, LAMPA, ENSAM Angers (Examiner)
• Mr. Nicolas SAINTIER, University Professor, I2M, ENSAM Bordeaux (Examiner)
• Mr. Viet Duc LE,Research Engineer, AMVALOR, ENSAM Angers (Examiner)
• Mr. Daniel BELLETT,Research Engineer, AMVALOR, ENSAM Angers (Examiner)
• Ms. Agathe FORRE, Research Engineer, Stellantis (Examiner)
• Mr. Pierre OSMOND, Research Engineer, CETIMI (Guest)
• Mr. Laurent ROTA, Research Engineer, Stellantis (Guest)

Thesis supervised by Mr. Franck MOREL and Mr. Nicolas SAINTIER and co-supervised by Mr. LE Viet Duc

Practical information

Location: Arts et Métiers Campus Arts et Métiers
Date: December 19, 2023
Time: 10:00 a.m.