# True or false?

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#### wavinwayne

Assuming that the clamping method, steel type, and all other conditions are equal, the amount of force required to bend a 1" diameter X 36" long steel shaft is the same, regardless of the case hardness of the shaft.

(Shaft size given is just a number I picked at random)

Originally Posted By: wavinwayne
Assuming that the clamping method, steel type, and all other conditions are equal, the amount of force required to bend a 1" diameter X 36" long steel shaft is the same, regardless of the case hardness of the shaft.

(Shaft size given is just a number I picked at random)

Within the realm of elastic deformation for both, the same.

The case hardened shaft will require more force to bend it into the plastic deformation region.

I take it then that the offering is "false" as presented?

..or is it assumed that you're required to over think it? I don't know anything about the subject matter, but ever True:False test that I run into has two or three "trues" when you assume depth beyond the presented conditions.

Originally Posted By: Gary Allan
I take it then that the offering is "false" as presented?

..or is it assumed that you're required to over think it? I don't know anything about the subject matter, but ever True:False test that I run into has two or three "trues" when you assume depth beyond the presented conditions.

The question wasn't asked in a way that allowed a meaningful true/false answer.

I suspect the answer the questioner wanted was "false".

XS650 is correct on both posts. There is no singular answer to the open-ended question. The real answer is "it depends".

..but it's not a question. It's a statement. The only question is whether it's true or false.

You're saying that the statement is lacking in information. From XS650's knowledge on the topic. I'd say that it's true. The statement didn't offer the condition of being in the "once the threshold of deformation is breached" realm.

Unless I misread what he responded with.

Did the hardening and crystal structure change have zero impact on the density of the shaft?

It's a horribly stated question.

XS650 got it, but I'm trying to nit pick.

Originally Posted By: oilyriser
Did the hardening and crystal structure change have zero impact on the density of the shaft?

Density has no direct effect on the topic being discussed. The property that was indirectly being questioned was Young's Modulus. It's quite constant for a wide variety of steels and even more independent of hardness in any real world sense.

To answer your question, if you case harden a precision machined 1.000 shaft 0.100 inches deep, it will no longer be a precision machined shaft
I don't have any numbers for you though.

Edit: a brief Google encounter indicates that I may have been too pessimistic. I saw some allusions to fairly precise dimensional control in case hardening. I doubt that that is just packing a red hot part in ground up bones and dried urine though.

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Would there not be a point at which the case hardening would cause the shaft to be brittle and then break upon bending?

heat treat additional to case hardening would do that, but I think that case hardening is the only variable being discussed.

I'd hypothesise that case hardening could add additional compressive stresses that would make the shaft a little bit stiffer than a non case hardened sample.

Just a guess.

And when did Kestas become a mod ? congrats mate.

Does adding carbon to steel affect its modulus at all? I suspect it would make a very tiny difference. Carbon-iron bonds probably behave differently from iron-iron bonds. But if both rods are chemically identical, stiffness should be the same in the elastic region.

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