Combining Hole-Drilling and Ring-Core Techniques

The hole-drilling and ring-core techniques are two well-known approaches to residual stress measurement. They apparently are complementary: in the former, a small hole is drilled in the specimen and residual stresses are estimated from the displacement/strain field around the hole; in the latter a small ring is milled and residual stresses are computed from the displacement/strain field inside the ring. However, owing to the different stiffness of the constraining region, their sensitivity and depth range are somewhat different. Although both techniques are implemented using strain gauges, the use of optical methods is nowadays largely accepted. As optical methods allow acquisition of data from both inside and outside the ring, in this work, we will try to exploit the different displacement release rates of the two regions to optimize residual stress measurement.