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

This paper presents an experimental method to evaluate the strains and the residual stresses in the case of laser welding. The workpiece is fixed rigidly to the table preventing distortion. Upon 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 melting lines or 12 transverse melting lines) and two modes of fixation (stiff or free in the plan XOY) were studied for every test. To determine the residual stresses in workpieces having undergone of the longitudinal master lines of melting, the latter ones were cut in samples perpendicular to the lines of melting. The measures realised in samples after their cut show that samples stemming from odd lines of melting lengthen whereas samples stemming from even lines of melting grow shorter with regard to their states before cut. Furthermore, the calculation of the intensity of the residual stresses in workpieces shows that the intensity of the residual stresses decreases with the decrease of the residual deformations. During welding by laser beam on thin pieces, strong deformations are observed on these pieces. Indeed, the real heat affected zone due to the laser beam / material interaction is superior to the heat affected zone estimated by metallurgical means.

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