Applications of the Incremental Hole-Drilling Method for Measurement of Non-Uniform Residual Stresses in Fiber Metal Laminates

In this paper, the incremental hole-drilling method is used to measure experimentally with accuracy non-uniform residual stresses in each ply of fiber metal laminate (FML) composites. Integral method was used for the approximation of residual stress. This method, considered a constant and uniform residual stress analysis at each hole-drilling depth increment. At the first, finite element method is used to calculation of the calibration coefficients matrix of the incremental hole drilling process. The calibration coefficients matrix determined by a finite element analysis can be used directly in the experiment. Calibration coefficients matrix used to relate the measured strain relaxation field with the existing residual stresses prior to the hole-drilling process. Also, for the experimental determination, released strains induced by high speed drilling process on FML composites with a stacking sequence of [AL/02/902]S have been quantified. At the end, the experimental measurements are compared with the theoretical predictions of the classical laminate theory. The good agreements between the experimental and theoretical results show that, incremental hole-drilling technique can be improved to be successfully applied for measuring non-uniform residual stresses in FML composites.