Electrical Resistivity and Yielding in Steel
Electrical Resistivity and Yielding in Steel
(OP)
Can electrical resistance be a good measure of the degree of yielding in a steel sample? If I have a steel plate and I measure it's baseline resistance and then subject that same plate to a cyclic bending test, would I get a measurable change in resistance? I know that certain metals will exhibit an increase in resistivity upon cold working, but does this phenomenon only occur for samples that plastically yield? If I did a cyclic fatigue test on a steel sample below the yield strength, would I observe an increase in resistance in the sample or would I have to enter the plastic range to observe any changes in resistance? On another note, is there another good method for measure the degree of yielding in a steel sample under cyclic loading?
Thanks,
Jeff
Thanks,
Jeff





RE: Electrical Resistivity and Yielding in Steel
RE: Electrical Resistivity and Yielding in Steel
RE: Electrical Resistivity and Yielding in Steel
Seems to me your question is a bit off the mark; how did the customer decide it had yielded, so as to get the refund? If your customer can tell, without any fancy test equipment, why can't you?
TTFN
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RE: Electrical Resistivity and Yielding in Steel
RE: Electrical Resistivity and Yielding in Steel
RE: Electrical Resistivity and Yielding in Steel
If the part has yielded it is either the wrong size or not flat. You can;t hide yielding.
Even if resistance of UT could detect it I don't know how you would distinguish the effect of fatigue from yielding. Both cause similar microstructural damage.
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Plymouth Tube
RE: Electrical Resistivity and Yielding in Steel
But, if the pieces must be replaced after slight yielding has occurred, then there is some change in the pieces that has occurs with yielding that makes the pieces unsuitable for service. Why not use whatever that change is to determine if yielding has occurred?
Or, is there something I am missing?
In practice, the best check to determine if yielding has occurred that I am aware of is to measure strain. Either a permanent strain after load is released or a non-linearity between load and strain indicates yielding.
The major issue I have a trouble with is that you use "slight yielding" (which is not very definitive) to define when the parts must be replaced. It sounds as if you are looking for definitive test to check for a subjective result.
rp
RE: Electrical Resistivity and Yielding in Steel
& recorded.
RE: Electrical Resistivity and Yielding in Steel
RE: Electrical Resistivity and Yielding in Steel
"cyclic yielding which could elongate the sample, and then subsequent return it to it's original shape."
Really? How?
I think the only way to determine whether something has yielded is to manipulate the piece in the same fashion that caused the yield to begin with. Unless the piece has the same stiffness as before shipment, it's likely to have yielded.
TTFN
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RE: Electrical Resistivity and Yielding in Steel
Jeff
RE: Electrical Resistivity and Yielding in Steel
While permanent strain is known to increase resistivity (due to increased dislocation and vacancy densities), this is next to impossible to determine by any practical method other than dimensional measurement. You probably don't even know what degree of strain was present to begin with, so you don't even have a reference. In a real-world steel I can't demonstrate 'slight' yielding metallographically, so I don't know how measuring resistivity would show it.
Yielding implies a permanent change in dimension; dimensional measurement is your best hope.
RE: Electrical Resistivity and Yielding in Steel
RE: Electrical Resistivity and Yielding in Steel
RE: Electrical Resistivity and Yielding in Steel
You can use a standard ultraonic inspection apparatus and piezoelectric transducer to measure the wave speed in your parts before they are placed in service, and after they are returned to you. If there is a change in density, this would probably be the most practical way for you to determine it.
Maui
www.EngineeringMetallurgy.com
RE: Electrical Resistivity and Yielding in Steel
RE: Electrical Resistivity and Yielding in Steel
Maui
www.EngineeringMetallurgy.com
RE: Electrical Resistivity and Yielding in Steel
If you mean that you want to be able to measure whether parts coming back from the field have yielded, the only reason that would be of interest is that they are now dimensionally out of tolerance.