In-Plane Residual Stress Analysis Combining Hole-Drilling and Moiré Interferometry
Residual stress measurement combining hole-drilling method and moiré interferometry has been developed to improve accuracy of stress measurement and has opened a new area for novel stress measurement technique [1, 2]. Validation of the technique under uni-axial loading in a previous work  has established the relationship between moiré patterns and the associated stress magnitude. Based on this preliminary work, a biaxial loading frame shown in Fig. 1 was developed to apply a biaxial state of loading on the test specimen, on which both the hole-drilling and moiré interferometry were then conducted. A four-beam interferometry optics and a hole-drilling set-up were integrated with the biaxial loading frame into a system, shown in Fig. 2 with which a known biaxial stress state can be applied to the specimen. The corresponding fringe patterns obtained from the moiré interferometry after hole-drilling were obtained to correlate with the corresponding stress state. This provides a quantitative data base for the relationship between in-plane residual stress and the moiré fringe pattern. Specimen grating with a frequency of 1200 lines/mm was applied to specimens made of 6061-T6 aluminum alloy (3mm x 50mm x 50mm). The milling guide was moved on a motorized precision stage at the speed of 1.25m/sec. The successive drilled hole depths were 0.3 to 1.2mm with 1.6mm in diameter.
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