• Sciences de l'ingénieur/Mécanique/Mécanique des fluides
  
• Sciences de l'ingénieur/Mécanique/Génie mécanique
  
• Sciences de l'ingénieur/Mécanique/Mécanique des matériaux
  
• Sciences de l'ingénieur/Génie des procédés
  
• Sciences de l'ingénieur/Matériaux
  
• Sciences de l'ingénieur/Mécanique/Thermique
  
• Sciences de l'ingénieur/Mécanique/Mécanique des solides
  
• Sciences de l'ingénieur/ Robotique
  
• Sciences de l'ingénieur/Mécanique/Matériaux et structures en mécanique
  
• Sciences de l'ingénieur/Traitement du signal et de l'image [eess.SP]
  
• Physique/Physique/Instrumentations et Détecteurs
  
• Sciences de l'ingénieur/Mécanique
  
• Physique/Mécanique/Génie mécanique
  
• Physique/Mécanique/Mécanique des fluides
  
• Physique/Mécanique/Mécanique des matériaux
  
• Physique/Mécanique/Matériaux et structures en mécanique
  

Fluid flow motion controls energy transfer in the weld pool and drives solidification process. Experimental investigation of fluid flow during welding is made particularly difficult by unsteady movements in the molten pool. In this paper, proper orthogonal decomposition (POD) based on images during gas tungsten arc welding (GTAW) on thin plates is used to investigate coherent structures revealed by thermal field in the molten pool. The POD method is based on fluctuating gray levels related to surface temperature. Based on this decomposition, two dimensional spatial modes and temporal coefficients are calculated allowing the identification of regions where temperatures are correlated. To explore the potential of POD method, weld beads were performed on 316L stainless steel plate at three welding speeds (2.3, 3.3 and 4.3 mm.s −1) and constant current (80A). These three conditions lead to different sizes of fully penetrated weld pools and different temperature distributions. Spatial modes and temporal coefficients provide information on temperature fluctuations along the free surface. Based on POD first modes, thermal field is reconstructed along the free surface to understand the heat transfer. Combining these results with side-view observations of the arc allows us to derive three dimensional flow patterns within the weld pool.

Ce document est un rapport d’étude qui présente les travaux effectués par l'équipe Assemblages Soudés (AS) du LMGC (Univ. Montpellier - CNRS, UMR 5508) dans le cadre du projet ANR Nemesis (Projet ANR-17-CE08-0036 du Programme AAPG 2017). Il s’agit d’une étude expérimentale réalisée principalement au cours du post-doctorat de Nicolas Blanc. Le but de cette étude est de pouvoir observer la solidification et le comportement du bain de soudage in-situ pour deux types d’alliages d’intérêt industriel : l’acier 316L et l’acier 22MnB5, intéressant de façon prioritaire respectivement EDF et Arcelor Mittal, partenaires du projet ANR. Les expériences doivent permettre d’obtenir des informations sur la taille et la forme du bain, sur les écoulements existants en son sein et sur le processus de solidification. Pour cela un dispositif similaire à celui utilisé par Alexis Chiocca [1] est utilisé. Le document est organisé autour de quatre chapitres. Le premier est dédié à un succinct état de l’art afin de rappeler le contexte scientifique général et l’utilité des observations réalisées dans la compréhension des phénomènes de solidifications pendant le soudage. Le deuxième chapitre est consacré à la présentation du dispositif expérimental spécifiquement conçu pour ce type de mesures et à la présentation des méthodologies d’étude. Les deux derniers chapitres sont consacrés à la présentation des résultats obtenus respectivement pour l’acier inoxydable 316L et les alliages 22MnB5.

A thermo-mechanical simulation of the wire + arc additive manufacturing (WAAM) process is presented in this work. The simulation consists in the deposition of 5 successive layers of 316 L stainless steel on a 316 L base plate. The thermo-mechanical analysis is solved in two dimensions under plane stress assumption. Nonetheless, the metal addition is taking into account in this numerical analysis. An increment of material is added at each time step. This numerical approach allows reducing the computational time. The temperature and residual stress fields are computed at each time step. Two patterns of deposition strategy are also investigated. It is shown that the longitudinal stress varies mainly along the vertical axis. A sample with 5 overlaid layers has been scanned with neutron diffraction technique in order to measure the final residual stresses. Both numerical and measured residual stresses are in good agreement. The Aster finite element software is employed for the numerical analysis.

Welding processes imply rapid solidification, in presence of high thermal gradient and strong fluid flows in the weld pool. This work presents, in the case of welding, an analysis of the coupling between solidification mechanisms and fluid flows at the macroscale and the microscale. An experimental setup was designed in order to observe in situ a fully penetrated weld pool generated on a Cu30Ni plate with a GTAW torch. At the macroscale, observations are carried out by three cameras: two cameras recording in visible light the top and the back side of the whole weld pool, and one infrared camera catching the thermal field on solid part at the back side. At the microscale, a high-speed camera, mounted with a microscope lens, is used to observe dendritic growth and fluid flows at the back side trailing edge of the weld pool. The observations provide a lot of data allowing analyses and discussions on the correlations between solidification mechanisms and fluid flows, with respect to welding parameters. Then, the experimental results are compared to theoretical results obtained from analytical modelling, in order to discuss the possible limitations of models and try to better understand the coupling between physical phenomena.

The purpose of this article is to investigate the influence of growth kinetic models and nucleation models on the grain structure predicted by cellular automata (CA) during bead on Cu30Ni thin plate. Temperature field is obtained with the computation of two-dimensional finite element model (FE). Based on these temperatures, a CA model simulates the evolution of the envelope of grains along the solidification front. It is shown that for the same temperature field, the grains structure is modified if the growth model changes. The influence of the nucleation law parameters is also discussed from a modelling point of view. Experimental size of the weld pool are compared with thermal results and EBSD maps are compared with grain structure prediction obtained with the CA algorithm.