APPLICATION OF X-RAY METHOD TO DETERMINE THE STRESS STATE OF RAILWAY PARTS

The method of determining the surface stress by X-ray method (by an example of steel samples of critical parts of railway transport) was examined taking into account the special surface preparation at the point of measurement. The features of the measurement surface stress by X-ray method were considered; the applicability of the designed layout of the portable X-ray diffractometer was shown. The diffractometer operates as follows. Changing the angle of diffraction in the presence of mechanical stresses leads to a shift of the diffraction peak on the recorded diffraction spectrum according to the peak position in the absence of stresses. The detector records the diffracted X-rays and passes the discrete information about the distribution of radiation intensity (which is captured by the detector) to the personal computer using an analog-digital converter. A special program “STRESSCONTROL” was developed for computer processing of the recorded diffraction spectra. The program allows to display graphically the diffraction spectra recorded by the detector, to control of diffractometer operation and to calculate the stresses using databases on metals and phases. Computer processing of the diffraction profiles is used to identify the position of the gravity center. The algorithm of the program involves the separation of the background, approximation of the data array to a curve and exact definition of the gravity center of the smoothed profile. The surface stresses on the fragment of the solebar of 20GL-type steel (after normalization and volume-surface hardening), cut from the box opening area with R55-radius, were measured. The surface stresses definitions for normalized fragment showed the results close to zero and the results of surface stresses definitions for the fragment with a volume-surface hardening showed a significant compressive stresses. Thus, the shape of the diffraction peak and the level of surface stress are directly related to the investigated steel microstructure features. In this case, the X-ray method of determining the surface tension may be an indicator of the surface state.

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