Effects of process parameters on the residual stresses measurements on titanium plates by using ESPI

Hole drilling (HDM) is the most widespread approach for measuring residual stress profile and it is, at the moment, the only technique to be ruled by a standard. Many improvements were introduced along the years and recently research papers investigated the feasibility to use optical systems to replace strain gage rosette as measurement tool of the strain field generated by the drilled hole. Generally speaking, the accuracy of the measurement is influenced by the proper choice of the experimental and analysis parameters. In this paper the effects of the choice of a proper analysis area, to be intended as the portion of the image captured by the CCD camera whose data are used to calculate the strain values, are shown. Furthermore the influence of the drilling rotation speed of the cutter used for drilling the hole is investigated. Experimental tests were performed on a Ti6Al4V specimen loaded in a four point bending frame up to 50% of the yield strength. Drilling speeds ranging between 5000 ÷ 50000 rpm were investigated by using an electronically controlled mill. Results obtained at different speeds and for different locations of the analysis area were compared with the theoretical expected value and with results from a numerical model implemented in ANSYS®.