Study of Residual Stress Distribution by a Combined Method of Moiré Interferometry and Incremental Hole Drilling, Part II : Implementation

An experiment is devised to implement the combined method of moiré interferometry and incremental hole drilling which was proposed in the companion paper. A unique experimental apparatus is designed to combine an optical set up for moiré interferometry with an incremental hole-drilling device. The apparatus maintains a constant relative position of a drilling device to the specimen while alternating moiré interferometry measurements with incremental hole drilling. The drill-bit can reenter the hole for each incremental step. The incremental hole-drilling device produces a precise control of incremental hole depth with an accuracy of 0.1 μm. The method is utilized to measure the residual stresses of two shot-peened materials: AS10U3NG aluminum alloy and the ten percent SiC_p reinforced aluminum composite-F3K10S Duralcan with a T6 heat treatment. Moiré fringe patterns with excellent contrast and high signal-to-noise ratio are obtained, which allows the extraction displacement data at the points very close to a hole boundary. In the experiment, a total number of ten steps of incremental hole drilling with an identical increment of 0.1 mm are performed. The fringe patterns of U_x and U_y displacement fields are recorded after each increment and the displacement data at the points of r = 1.2r₀ are extracted consequently. They are used to determine the nonuniform residual stress distributions of surface and subsurface layers of shot-peened materials. The results indicate that the medium level of approximately equibiaxial compressive residual stresses exist within a 0.3 mm layer.