Wire Electric Discharge Machining for Residual Stress Measurement
In the Crack Compliance Method we measure residual stress by using wire EDM to incrementally cut a slot into a part while measuring released strains.
In Wire EDM (electric discharge machining, a.k.a. spark erosion) a wire that is electrically charged with respect to the workpiece is used to make a cut. As the wire approaches the workpiece, a spark jumps the gap and electrically erodes away the material.
Advantages of Wire EDM for Measuring Residual Stress
Aren't EDM machines expensive?It doesn't really matter. They are available everywhere. If you're at a big company or university, you probably have at least one. If not, most urban areas will have machine shops with EDM machines that will work with you for an hourly rate.
Other cutting methods for crack compliance measurementsOther methods have been used for making the cut
W. Cheng, I. Finnie, M. Gremaud, and M.B. Prime, "Measurement of Near Surface Residual Stresses Using Electrical Discharge Wire Machining," J. Eng. Mat. & Tech., 116, 1-7, 1994. Sorry, I don't have an electronic version.