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Los Alamos National Laboratory The Slitting Method for Residual Stress Measurement:  : Method Background
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What is the slitting (compliance) method?

About the method:

Sketch of incremental slitting
  • A slot is machined incrementally into a part containing residual stress
  • The slot releases the residual stress normal to the face of the slot, and the part deforms
  • Surface strain gauges measures the resulting strains as a function of slot depth
  • The strains are then used to solve for stress as a function of depth
See the Theory section for a graphical illustration of how this works

If it's similar, why is it better than hole drilling in many cases?

  • Put a strain gage on the back face and you can measure stresses all the way through the thickness, not just near the surface.
  • Increased "invertability" means you can measure stress variation with depth better
  • EDM machining is a very "gentle" machining process. With hole drilling, you may introduce stresses and increase your errors
  • For further comparisons see the section on comparing with other methods

More Detailed Information:

  • Theory - How you do the calculations
  • Literature , a little discussion on the history of the method, and some downloadable papers
  • How do you make the cut? Wire EDM (spark erosion) is one way and it makes a very thin slot and puts in almost no stress

Where does the name come from?

The technique is named after the compliance method for measuring crack length in fatigue specimens. There, a strain gage on the back face of the specimen measures strain as a function of load. The slope of this line gives the crack length.