Mesure de contraintes résiduelles dues au soudage et au soudage-martelage par micro-profil de surface

Nasri, Hassan (2007). Mesure de contraintes résiduelles dues au soudage et au soudage-martelage par micro-profil de surface. Mémoire de maîtrise électronique, Montréal, École de technologie supérieure.

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Résumé

Le soudage est un procédé qui induit des contraintes résiduelles dues aux déformations plastiques et aux changements de phase qui se produisent dans la zone affectée thermiquement (ZAT). Pour inverser ou minimiser les contraintes de tension dues au soudage, des traitements de surface sont utilisés. Cette étude s'interesse particulierement à l'analyse de l'effet du martelage sur les contraintes résiduelles déjà en présence dues au soudage. Le protocole de mesure retenu pour la mesure des contraintes résiduelles est la méthode de contour.

Cette méthode s'avère très prometteuse, elle est basée sur la relaxation des contraintes suite au procédé de coupe à l'EDM. Les déplacements mesurés par laser sur la surface coupée sont traités et approximés par une surface polynomiale qui est utilisée pour imposer les déplacements mesurés aux noeuds d'un modèle par éléments finis. La solution de ce problème donne les contraintes normales au plan à l'origine de ces micro-déplacements. L'aboutissement final est le champ de contraintes sur la totalité de la surface de coupe. Ce protocole de mesure sera appliqué sur une préparation soudée et une autre soudée et martelée de plaques d'acier carbone A516.

Résumé traduit

In the area of mechanical fabrication, various methods of assembly are employed. It is of utmost importance to know the fabrication induced stresses in order to prevent these assemblies from collapse. Various methods are used to measure these stresses, each with its own limits and degree of reliability. The most accessible methods of measurement of residual stresses are point methods, which is unsatisfactory and points out to the need for establishing a method of measurement allowing the evaluation of the stress distribution on the whole surface.

The new proposed method of measurement is very simple to implement. Known as the micro-profile method, it gives the distribution of the stress component normal to a plane generated by wire cutting. It is based on stress relaxation. This method has proved to be efficient for estimating the residual stresses inherited from fabrication. The implementation of this method simply requires a careful cut carried out by an electric discharge machine (EDM) at the point of interest, a laser profilometer scan of the released displacements, along with program handling for treating data and some finite element basic calculations.

Released displacements at the cut surface are first measured using the laser-camera. Programs are then used for re-orienting the target plane and for data filtering and smoothing. Finally, these displacements are prescribed at some specific nodes of the surface of a finite element model of the cut piece. The linear elastic static module of the finite element code is used to solve the normal stress components at the surface, which represent the residual stresses that were acting on that plane before wire cutting. The calculated residual stresses were compared with that obtained from various experimental methods, namely from biaxial strain gages installed on the surface of the plate prior to EDM cutting, from the hole-drilling technique (RS200), and finally from by X-Ray measurements (XRD).

With the first sample, stresses obtained from the micro-profile method and from biaxial gages are comparable and show the same trend. However, contrary to the hole-drilling method, the maximum residual stress is not in the weld centerline. This offset was attributed to a phenomenon of material plastic yielding that occurred during cutting, because of a lack of restraint of the plate during the cutting operation.

On a second sample, also as welded, stresses obtained from the hole-drilling method and from the XRD method revealed a maximum stress at the plate weld centerline, and a symmetrical stress distribution relative to this axis. This distribution of stresses is also observed by the micro-profile method. A good correlation is then found between the three measurements.

The last sample, which was welded and hammered, showed the ability of the micro-profile method to measure the compression induced hammer-peening operation. Again a good correlation was found between the three measurement techniques. These results are very promising and demonstrate the versatility of the micro-profile method to analyze virtually any surface treatment process. This also allowed introducing the study of the influence of hammer-peening on the reallocation of tensile stress induced by welding.

Type de document:	Mémoire ou thèse (Mémoire de maîtrise électronique)
Renseignements supplémentaires:	"Mémoire présenté à l'École de technologie supérieure comme exigence partielle à l'btention de la maîtrise en génie mécanique". Bibliogr. : f. [106]-107.
Mots-clés libres:	Contrainte, Evaluation, Martelage, Mesure, Methode, Micro-Profil, Plaque, Preparation, Residuel, Soudage, Soudage-Martelage, Soude, Surface, Validation
Directeur de mémoire/thèse:	Directeur de mémoire/thèse Champliaud, Henri
Codirecteur:	Codirecteur Lanteigne, Jacques
Programme:	Maîtrise en ingénierie > Génie mécanique
Date de dépôt:	12 avr. 2011 15:01
Dernière modification:	01 déc. 2016 01:07
URI:	https://espace.etsmtl.ca/id/eprint/594

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