Welding Metallurgy of

We propose a new method for a qualitative estimation of camera motion from a video sequence. The proposed method suggests to use the properties of vanishing point perspective to complete the information obtained from apparent motion, that is to use a cooperative estimation from several visual cues. Focal length and rotational parameters are first retrieved using perspective, then apparent motion is used to retrieve remaining parameters. The proposed method can retrieve all seven camera motions, including combination of motions. Experimental results confirm the usefulness of the additional information gained from perspective.

Liste des tableaux

A Method of Shrinkage Prediction and Its Application to Steel Casting Practice

Hot cracking in welding is a complex phenomenon due to coupling between process, metallurgy and mechanical loading. A methodology based on process simulation, simple microstructural prediction and a pressure model along columnar grains is developed in order to integrate all factors that influence hot cracking. The model is based on some developments of Rappaz, Drezet and Gremaud and takes into account the influences of grain morphology, mechanical and welding thermal loading, on hot cracking. The model based on the microstructure behaviour is able to predict crack onset location in columnar grains on 6061 aluminium alloy.

/pdf/modelling-hot-cracking-in-6061-aluminium-alloy-weld-metal-c3db9ysa4c.pdf

Modelling hot cracking in 6061 aluminium alloy weld metal with microstructure based criterion

In this study, the effects of Yb: YAG laser welding parameters on the microstructure and mechanical properties of AA6061-T4 joints were analysed. Samples without any welding defects such as porosity, melt pool collapse, and hot cracking were produced with different welding parameters. Energetic processing parameters had a significant influence on the fusion zone (FZ) and heat-affected zone (HAZ) microstructure and dimensions, in addition to local and global mechanical properties. The weld bead width increased with increasing power and energy densities and reduced the weld bead tensile properties. High welding travel speed produced a more elongated weld pool and ripples resulted in a ‘V’ shape. A significant quantity of axial heterogeneous nucleation was observed in the FZ centre of these weld beads because of the low-energy density. In contrast, low welding travel speed produced C-shaped ripples and a few axial grain nucleation sites in the FZ. The latter was evidence of a slower solidification rate. Dendrite secondary arm spacing measurements confirmed this hypothesis. It was observed that axial grains in the FZ centre improve the weld bead tensile properties. Compared to the base material (BM), the hardness in the FZ was reduced and identical in the HAZ. The FZ hardness depended on the welding parameters. Digital image correlation (DIC) strain measurements indicated higher deformation near the FZ, but when geometrical defects were removed, the FZ deformed more homogeneously.

Effects of welding parameters on the microstructure and mechanical properties of the AA6061 aluminium alloy joined by a Yb: YAG laser beam

L'objectif de ce travail est d' etudier, au travers d'un essai simple, l'influence des parametres procedes sur la microstructure et sur le chargement mecanique dans le but de minimiser le risque de fissuration a chaud. Un essai original a ete developpe consistant a appliquer une precontrainte de traction controlee dans la direction de soudage sur une tole d'alliage d'aluminium 6061 de faible epaisseur, avant de realiser une ligne de fusion avec le procede TIG. Des analyses de la microstructure de solidification ont permis d'identifier des longueurs caracteristiques traduisant l'influence des parametres procedes sur la morphologie des grains. La modelisation de cette microstructure, a partir de donnees thermiques issues de la simulation numerique, a permis de predire la microstructure obtenue dans differentes conditions de soudage. L'application d'un critere de fissuration a chaud prenant en compte la microstructure predite permet d'integrer l'influence de la morphologie des grains sur la prediction de l'initiation de la fissuration a chaud. Pour terminer, des solutions d'optimisation du procede de soudage, vis a vis du phenomene de fissuration a chaud, sont proposees en tenant compte des interactions procede/ materiau.

https://tel.archives-ouvertes.fr/tel-00713746/document

Aurélie Niel

Papers

Étude et modélisation du phénomène de fissuration à chaud en soudage à l'arc : Application à l'alliage d'aluminium 6061.