Influenceing Charpy Impact Testing

Theoretically then, if you had a small stress crack, then you could strengthen the material by just grinding out the crack? Not that this would have any practical application.

Sort of - you won't "strengthen" the material in the sense that it will be stronger than it was with no defects - but it will have higher fatigue strength if you smooth/grind out the crack rather than leave it with a sharp tip (you must ensure that you don't remove excess material beyond the crack tip - because that would make it weaker)

This situation is similar to a stress concentrator on a rotating shaft - it is preferred to have a radiused shoulder on diameter changes, rather than a sharp corner.

Thank your for the clarification and yes, I did word my question improperly as I would not assume to actually make the material itself stronger by grinding it. I am still learning the importance of proper terms. Again, thank you, XMech.

XMech, why in the world would you perform fatigue testing on an impact sample?

To me it seems the form missed the function and the fit is off in left field kinda doin' its own thing.

"To me it seems the form missed the function and the fit is off in left field kinda doin' its own thing."

Well said.

I did not (mean) to say to perform fatigue testing on an impact sample. I just meant to give a well known example of stress concentrations.

The question is of a hypothetical situation anyway.

Also from ASTM E23 (hopefully it is legible because it describes the results of size effects):

When small cracks show in material, an old method of preventing them spreading was to drill a hole at the end of the crack. This reduced the stress concentration and discouraged the crack from growing.

If the radius at the base of the notch is reduced, the Charpy test will give a smaller result.

It has been a while since I did Charpy but if I recall correctly in ASTM E23, one measures the depth of the crack and subtracts this from the area of the test sample (width x depth). Then when the hammer hits the sample the amount of energy required to fracture it is measured and this number is compared to the area for the reported impact strength.

So as long as everything is measured correctly, and the fracture surfaces don't trend towards large shear lips you should be ok since its a self correcting test. Of course I would recommend testing more than 10 samples to be sure and report your data as "ASTM Modified" or "Not to ASTM Standard".

Smaller radius (close to be looks like crack) will leads to higher stress concentrations, and inturn a failure will be happened at relatively smaller loads, i.e. decreases the resulting impact value.