nanoindentation method

In this study, variations in the residual stresses distribution were studied in different hole-making strategies including; conventional, multi-step drilling and helical milling. Residual stresses were measured for 12 perforated samples made of 4340AISI steel, using nanoindentation method. The results showed the highest near-surface compressive residual stress in the multi-step drilling (up to 373.5 MPa). Also, due to the phase transformation on the surface, the effect of plastic work was eliminated and tensile residual stresses up to a maximum of 114.7 MPa were measured in the drilling process. On the other hand, decreasing the cutting speed and increasing the feed rate raised the compressive stresses up. The trend exception was formation of the white layer in the drilling process. Comparison of the stresses measured on the reference sample also showed a difference of about 28.6% between the two methods of XRD and nanoindentation, which shows an acceptable repeatability of the measurement using nanoindentation method.