# Torsional strength at high temperature

#### CFurner

High school student here

I am designing an experiment to test the effect of temperature on the torque required to twist a peice of metal, and need some advice on where to start researching. What I need help with is A) finding a table of the torque required to twist steel when cold, and B) finding some equation/principle/law that relates the temperature of the metal to the torque required to turn it.

1. I plan to use mild steel, probably annealed if I can get it
2. I can go very high heat wise, and plan to use a laser thermometer to measure the temperature of the metal
3. I will be using a setup that uses weights to produce torque, and that isolates the motion to only rotational (as opposed to bending downwards)
4. Im open to any neccessary/beneficial changes to the experiment, any and all advice is greatly appreciated.
5. I don't have an endless money tree so any reccomendations of buying some huge expensive torsion testing machine will be fruitless.
6. I probably have screwed up some of the terminology, sorry in advance, tell me if I did.

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#### Dr.D

As I read your question, you speak of twisting the piece of metal which I take to mean you want to induce permanent deformation. If this is not the case, and only elastic deformation is required, that is a different problem.

To permanently deform a piece of metal requires plastic deformation, that is, involving stresses that exceed the yield point. The yield point is strongly related to material temperature, declining with increasing temperature.

The problem is complicated by the fact that permanent deformation does not necessarily require yielding at all points in the material, only enough that the new equilibrium form is the desired deformed shape. Thus, part of the material may still be in the elastic range, attempting to return to the original shape while other parts have yielded and have a new free shape. The result is locked up stress within the body.

Before you do your experiment, I suggest that you seek out information on the temperature dependence of the yeild point for the material involved, and then attempt to predict the deformations expected for specified loads. This should help you plan your experiment.

.

#### CFurner

As I read your question, you speak of twisting the piece of metal which I take to mean you want to induce permanent deformation. If this is not the case, and only elastic deformation is required, that is a different problem.

To permanently deform a piece of metal requires plastic deformation, that is, involving stresses that exceed the yield point. The yield point is strongly related to material temperature, declining with increasing temperature.

The problem is complicated by the fact that permanent deformation does not necessarily require yielding at all points in the material, only enough that the new equilibrium form is the desired deformed shape. Thus, part of the material may still be in the elastic range, attempting to return to the original shape while other parts have yielded and have a new free shape. The result is locked up stress within the body.

Before you do your experiment, I suggest that you seek out information on the temperature dependence of the yeild point for the material involved, and then attempt to predict the deformations expected for specified loads. This should help you plan your experiment.

.
Thank you for your reply, that should help a lot with my research and experimental design. I do want to permanently deform the metal, so your suggestion about the yield point was very helpful.

"Torsional strength at high temperature"

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