Effet des contraintes residuelles sur les parametres modaux dans les structures soudees.

摘要

Manufacturing and forming processes induce residual stress in mechanical pieces. Welding process generate a high residual stress concentration at the weld seam vicinity. This residual stress can have a serious impact on the piece mechanical behavior. In order to reduce residual stress level, thermal or vibratory relaxation treatments can be required. But, even after a relaxation treatment, some residual stress may remain in the piece. The evaluation of the residual stress among remaining can hardily be achieved because of the measurement techniques complexity. In practice, many methods and techniques can be used to evaluate the welding residual stress. However, most of the time, those techniques can not always be performed and can lead to imprecisions. Previous studies have shown that vibratory response could be affected by the welding residual stress. Following those observations, modal analysis appears has an alternative method to evaluate the residual stress among contained in a piece. Combining experimental modal analysis with numerical calculation using the finite element method, it is possible to establish a relation between a residual stress state and modal parameter modifications. Experimental modal analyses have been performed on thin plates in order to measure residual stress effects on modal parameters. Natural frequencies variations caused by residual stress have been observed according a wide frequency range. Relaxation treatment permitted to recover the original natural frequencies values for almost all modes. Thermo-mechanical finite element analysis is used to calculate the welding residual stress. Modal analysis performed following each solution steps during the welding and the relaxation treatment enable to track the effect of residual stress on modal parameter. Numerical results are compared to experiment measurements.;Keywords : residual stress, welding, modal parameter, thin plate, numerical calculation, finite element.