Analysis of Residual Stresses in Steel Welded Parts Using Ultrasounds

Abstract

<span><p><span style="font-family: Times New Roman; font-size: medium;" face="Times New Roman" size="3">Welding is an assembly process used in different industries. The residual stresses influences fatigue behavior, fracture strength, corrosion resistance and for these reasons knowing their values are important. During time, many destructive as well as nondestructive methods to evaluate residual stresses were developed. Stress is evaluated by inducing a sound wave with the frequency of several megahertz into the sample and measuring velocity related parameters. Besides stress which affects sound velocity there are many others characteristics of metals with same influence and for this reason sorting from different influences made the estimation difficult. On another hand ultrasonic technology has many wave modes to investigate materials including bulk wave (longitudinal and shear wave), surface wave (Rayleigh) every mode offering unique parameters for extracting information. Of the several characteristics that may be used to measure stress the most exploited seems to be sound velocity dependence on the elastic modulus. </span>Our research to estimate residual stress into steel welded parts is based on dependence between sound velocity and elastic modulus using longitudinal sound wave. To conduct the experiments was designed sample as a frame. The sample was loaded using adapted equipment and the results were used for FEA tools (SolidWorks SimulationXpress) to obtain the distribution of stresses and displacements. This approach allowed the location of points of interest to the investigation with ultrasound. The ultrasound investigation was made and presented in comparative tables<strong><span style="text-decoration: underline;">. </span></strong>It is found that the variation of the velocity of sound for the two charge states of the piece is, on average, 5.8 per thousand. Particular values of residual stress values are observed for the points corresponding with weld or fusion zone and heat-affected zone. The ultrasonic investigation permits the evaluation of bulk stress state of welded components with acceptable accuracy.</p>