Evaluation of stresses in components using ultrasonic and electromagnetic techniques

Complementary to the established techniques to evaluate stress states, electromagnetic and ultrasonic techniques permit the evaluation of stresses in surface layers and in the bulk of components, respectively. One advantage of these techniques is the possibility of a fast evaluation of stress states, enabling a continuous analysis along traces to get an information about the stress distribution and the stress inhomogeneities. A disadvantage of both techniques is the influence of changes of micro structural states on the measuring quantities. In case of the electromagnetic techniques, calibrations have to be done, using representative samples in tensile test experiments. The quantitative evaluation of stress states using ultrasonic techniques assumes the knowledge of the acousto-elastic constants. The influence of the micro structural state on the electromagnetic and acousto-elastic quantities has been studied. Depending on e.g. the steel grade, the hardness, the welding parameters, the micro structural state as well as the texture differs. It is found that the texture and micro structural influence on the acousto-elastic constants is not as significant as it was expected. Applying multiple regression algorithms on the electromagnetic quantities, the microstructural states influence can be suppressed. Results of ultrasonic and/or electromagnetic stress analysis on rolled plates, in and around welds, along the length of rolls and gear shafts and along a part of a pipeline were mapped. Comparisons with the results of an establishes technique show the reliable application of both techniques. The presentation describes the experimental results and discusses the applicability of the electromagnetic and ultrasonic technique and the benefits of the measurements over large areas of the component