Ultrasonic Stress Measurement in Welded Component by Using Lcr Waves: Analysis of the Microstructure Effect

Abstract

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.