Measurement of Residual Stresses by the Hole-Drilling Strain Gage Method

Alignment Rendler and Vigness observed that "the accuracy of the (hole-drilling) method for field applications will be directly related to the operator's ability to position the milling cutter precisely in the center of the strain gage rosette." More recent studies have quantified the error in calculated stress due to eccentricity of the hole. For example, with a hole which is 0.001 in (0.025 mm) off-center of the 062RE or 062UL rosette, the error in calculated stress does not exceed 3% (for a uniaxial stress state) (Refs. 9 , 10 , 11 ). In practice, the required alignment precision to within 0.001 in (0.025 mm) is accomplished using the RS-200 Milling Guide shown below. The milling guide is normally secured to the test object by bonding its three foot pads with a quick-setting, frangible adhesive. A microscope is then installed in the unit and visual alignment is achieved with the aid of the four X-Y adjustment screws on the exterior of the guide.

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