Consideration on temperature fields and internal radius of analysis in HDM+ESPI residual stress measurements

Hole drilling is the most widespread method for measuring residual stress. This method is based on the principle that drilling a hole in a material causes stress relaxation; by measuring the resulting strain it is possible to calculate the initial residual stress. Recently optical systems were introduced to replace strain gage rosette since they can provide full field measurements with high sensitivity. When using ESPI technique, the analysis area, that is to say, the portion of the image which must be used for measuring strain is defined by the operator. Proper choice of this area can be affected by many factors. In this paper, in particular, the influence of drilling rotation speed is investigated. To this scope measurements at three different speeds were carried out and for each speed the temperature field around the hole was measured by using a thermocamera.