Calibration Coefficients Determination Through Fem Simulations for the Hole-Drilling Method Considering the Real Hole Geometry

The residual stress measurement by the Hole-Drilling Method (HDM) is recommended by the ASTM E837.13a for a range of hole diameters and inspection depths. To calculate the stress distribution, calibration coefficients are applied according to the hole diameter and the rosette-type used in the measurement. However, the standard is based on a blind hole which is orthogonal to the specimen surface and with a flat bottom geometry. The commonly used cutting tools in the HDM are end mills, which usually have a chamfer or fillet radius in the corner of the edges. Consequently, chamfers or fillets are directly transferred to the blind hole bottom geometry. This real geometry is not considered by the tabulated calibration coefficients. In order to provide more accuracy to the HDM, this paper provides calibration coefficients determined by FEM simulations according to the real blind hole geometry. Uniform residual stress measurements were made in the A36 steel, AISI304L stainless steel and AA6061 aluminium alloy and evaluated with the coefficients tabulated by the standard and coefficients simulated to the real blind hole geometry. Considerable differences were observed, especially in the first two increments for the measured principal stresses, namely sigma 1 and sigma 2.