Welding, which is a largely used process in the mechanical manufacturing, well known to induce high-level residual stresses. The level of residual stresses is of great importance for the lifetime of welded components used in mechanical engineering industry. The use of the ultrasonic method for the evaluation of the residual stresses is based on the acoustoelastic effect, which refers to the change in velocity of the acoustic waves propagating in a strained solid. In the case of welding, the microstructure modifications observed in the heat affected zone (HAZ) and the melted zone (MZ) also induce variations of the velocity of the acoustic waves. The superposition of the two effects, stresses and microstructure, results in over-estimating the levels of stresses. This work which was completed in collaboration with CETIM is a contribution to this problem. The experimental study was carried out on P460HLE and P265 steels welded sheets. The results obtained by the ultrasonic Lcr wave technique were compared with those obtained by the hole drilling technique. This work confirms the possibility of evaluating the residual stresses induced by welding using the ultrasonic method.
The good control of residual stress level in mechanical components is an important factor, particularly for a good fatigue strength of these components. This paper presents advances obtained at the technical center for mechanical engineering industries (CETIM) in the field of development of an ultrasonic method for stress measurements. This method is potentially advantageous because it is nondestructive, has good portability, and is easy to use. In the paper are discussed the results obtained with ultrasonics on steel welded plate, and a comparison is made with stress measurement obtained by incremental hole-drilling method, and X-ray diffraction. These results are also validated by thermal relaxation of the plates. The paper discusses also the microstructure influence on ultrasonic measurements and methods for adjusting the ultrasonic measurements to improve the agreement with results obtained from other techniques. In conclusion is emphasized the interest for studying the ability of the ultrasonic residual stress measurement method in different industrial cases.
Welding, which is a largely used process in the mechanical manufacturing, is one of the causes of high-level residual stresses. The level of residual stresses has a great importance for the life time of welded components used in mechanical engineering industry. The ultrasonic technique may be used to determine the residual stresses. The technique is based on the acoustoelastic effect, which refers to the change in the velocity of ultrasonic waves propagating in strained solids. Previous studies were carried out to evaluate residual stresses by using ultrasonic methods, but they do not enable to exactly determine the stress values in the heat-affected zone (HAZ) and the melted zone (MZ). This paper describes the experimental procedure of ultrasonic stress measurements applied to welded manufactured joints for different steel grades such high elastic limit material. It is noticeable that, to take into account of microstructure influence on ultrasonic behavior of the weld, the measurement were calibrated on samples machined in the melted zone and in parent metal. The results obtained by the ultrasonic Lcr waves technique were compared with those obtained by “reference” techniques such as hole-drilling. This work confirms the possibility of evaluating the residual stresses induced by welding using the ultrasonic method, and shows improvements obtained in taking into account of metal microstructure for evaluating stresses in the welds.
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