The problem: residual stress on bearing ball
Subsurface properties of a hardened steel sample can be studied by electrochemically removing material from the surface and measuring the residual stress (RS) as a function of depth.
Customer wanted to know the RS depth profile of a Ø 4 mm ball bearing. To satisfy the standard EN 15305 Non-destructive testing. Test method for residual stress analysis by X-ray diffraction a 0.3 mm collimator was chosen to be used in the measurements. With a conventional X-ray diffraction device, a single RS measurement with reasonable data quality would have taken 1h 55 minutes. In a RS depth profile typically 4-6 individual RS measurements are carried out while electropolishing material in between. Measuring one depth profile would have taken 34.5 hours of measurement time when measuring RS in three directions. Instead of a traditional diffractometer the DR45 with its 2D detectors was chosen for the task in hand.
The testing method: X-ray diffraction
Prior to measurements the ball bearing was affixed to an aluminum block with chemical metal epoxy padding so that galvanic contact with the block was maintained and the ball could be kept still during the depth measurements.
Residual stress measurements were done using the XStress DR45 and XStress Studio software. Integrating the 2D detector data (Fig. 2) along the Debye-Scherrer ring, the diffraction peak data showed in Fig. 3 could be gathered in exposure time of 3 s. The measurement time was 3 minutes per depth when the RS was measured in three directions. This means that 18 minutes of measurement time per depth profile was used.
The measured residual stress profile of one sample is shown in Fig. 4.
Instruments used for this application
Xstress DR45: Newest generation of X-ray diffractometers delivering high quality data faster than ever before.