Author: Jonas Holmberg, RISE IVF
The study: surface residual stress mapping on gears
For verification of the residual stress impact, normally, only one position is measured. However, in this work we wanted to study how sensitive the selection of the measurement position is for the process of case carburization and the subsequent shot peening.
The testing method: X-ray diffraction
The residual stresses of two different gear tooth, as seen in Figure 1, were mapped across the gear tooth using small incremental sideway steps of 0.5 mm for positions at top, center, bottom of the flank and at the root of the gears.
The surface mapping across the gear teeth is shown in Figure 2A) for the case carburized gear and in Figure 2B) for the shot peened gear. The results, clearly show that the position of the measurements has an impact depending on the process: case carburized vs. shot peened.
- For the case carburized gear, a slight offset in residual stress values is seen between the root and the three positions on the flank.
- For the shot peened gear, a general offset of 100 MPa is seen between the bottom position compared to the top and the center positions.
The surface stress measurements indicate that the stresses differ a lot between the root and the flank for the shot peened sample but only slightly for the case carburized gear. It is also shown that the selection of the measurement position is less critical in the middle part of the gear tooth, while the edges of the gear show variations. This indicates that selection of the measurement position on the case carburized gear is less critical on the flank while on the shot peened gear the bottom position of the flank has lower compressive stresses which may be important to verify.
Instruments used for this application
The residual stresses were measured with the Xstress DR45. The Xstress DR45 allows for fast measurements even when a small measurement spot (collimator) is used; in this case a 1 mm collimator and an exposure time of 1 s per tilt were used.