X-ray determination of the stress state of rolling-stock components

Abstract

For the example of steel rolling-stock components, the X-ray determination of the surface stress is considered, with special preparation of the surface at the point of measurement. The effectiveness of this method when using a prototype portable X-ray diffraction system is demonstrated. The operating principle of that system is as follows. In the presence of mechanical stress, the diffraction angle changes, and the diffraction peak is shifted in the recorded diffraction spectrum. The diffracted X-rays recorded by the detector are converted to digital information regarding their intensity distribution, by means of an analog–digital converter, and sent to a PC. STRESSCONTROLL software is developed for computer analysis of the diffraction spectra. That software displays the diffraction spectra in graphical form, controls the operation of the diffraction system, and calculates the stress by means of a database on metals and phases. The computer analysis includes determination of the spectrum’s center of gravity. The software separates out the background, approximates the data set as a curve, and permits precise calculation of the center of gravity of the smoothed profile. The surface stress is determined for fragments of a 20GL steel solebar cut from the edge of a bearing aperture of radius R55, Before testing, the fragments are subjected to normalization or to bulk–surface quenching. The surface stress is found to be close to zero for the normalized fragment, while considerable compressive stress is observed for the quenched sample. Thus, the shape of the diffraction peak and the level of surface stress are directly related to the microstructure of the steel. In that case, the X-ray determination of the surface stress may provide information regarding the state of the surface.