Finite element analysis of calibration factors for the modified incremental strain method

To modify the incremental strain method used to evaluate non-uniform residual stress, a finite element analysis (FEA) of the reference model used to describe a hole-drilling test was conducted. The calibration factors for the x and y directions were obtained from the analysis and then their differences were compared under various loading conditions. A hole-drilling test using a steel plate as the reference specimen was introduced, and under the pure bending load, strain relaxation was measured at each hole-drilling step to determine the calibration factors. Although the calibration factors in the x and y directions varied with the boundary conditions used in the FEA, their differences were reduced to zero for all depths when the prescribed loads as the boundary conditions in the x and y directions became the same. In addition, it was analytically and experimentally confirmed that the calibration factors did not vary with the direction. Accordingly, by making the calibration factors equal in the x and y directions in the modified equation for the incremental strain method, no singularity is produced in the stress calculations.