The Eddy current technique for determining residual stresses in steels

Eddy Current (EC) testing has been successfully employed to determine the residual stress patterns in steels. Since any change in residual stress in ferromagnetic materials produces changes in the electrical and magnetic properties of the material, EC can be used to detect these changes in residual stress as changes in the impedance of the EC results. Residual compressive stresses in steel are desirable in fatigue applications, while tensile residual stresses are not. By employing an NDE technique (EC) that is incorporated into the early stages of the manufacturing process, steel parts not meeting the required residual stress can be identified and discarded. In this way, the service Life can be improved dramatically. In our experiments, excellent correlation was established between the residual surface stress as determined by the X-ray diffraction technique and the EC technique.