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Experimental Method of Evaluating the Strains and Residual Stresses in Laser Welding
Y. Zamachtchikov, C. Marta, P. Vantomme, P. Deprez and A. Deffontaine

This paper presents an experimental method of evaluating the strains and residual stresses in the case of laser welding. The workpiece is fixed rigidly to the table preventing distortion. On removal the residual stresses relax resulting in a change of shape. A 1.5 kW continuous wave (CW) CO2 laser (Cilas CI 2000) was used as the welding source. The hypoeutectoid steel used for this study has a content in 0.05 % carbon and a content in 0.26 % manganese. Two directions of welding (6 longitudinal tracks and 12 transverse tracks) and two modes of clamping (stiff or free in the plan XOY) were studied for every set of parameters. To determine the residual stresses in workpieces having undergone the longitudinal master tracks, some were cut perpendicular to the tracks to provide specimens. Measurement undertaken on specimens after cutting show that specimens originating from odd tracks of melting lengthen whereas specimens from even tracks grow shorter compared to the states before cutting. Furthermore, a calculation of the magnitude of the residual stresses in workpieces shows that the magnitude of the residual stresses decreases with decreasing of residual strain. During welding by laser beam of thin pieces, strong deformations are observed. In fact, the real heat affected zone due to the laser beam / material interaction is larger than the heat affected zone measured by metallurgical means.

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