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Thermal Expansion - Elastic and Plastic Deformation

Thermal Expansion - Elastic and Plastic Deformation

(OP)
Hi Everyone,

I have a general question here which may or may not be a stupid one but I'll ask it anyway.

If a material, let's say mild steel for example, is heated up it will expand. When it cools it will contract again. Does a stress-strain curve as seen in typical tensile tests apply to thermally induced strain? I suppose another way of putting it is: can you have thermally induced "plastic" and "elastic" deformation in a metal.

I am asking because I have a problem where something will be heated to a given temperature and I would like to know whether or not it will contract to its original dimension, or contract to a dimension different to the original.

If anyone knows any good resources on this topic please it would be helpful if you could share them.

Many thanks,

Tom

RE: Thermal Expansion - Elastic and Plastic Deformation

If your specimen is not physically constrained, and is free of residual stresses, it will return to its original configuration and a stress-strain curve will mimic the sample prior to the heating event.

RE: Thermal Expansion - Elastic and Plastic Deformation

There is no direct relation between temperature and stress. Temperature changes do cause dimensional changes which are not the same as elastic or plastic strain.

I have one additional comment to help improve your writing style. The first two sentences of your post added nothing to your question. They only projected your insecurity.

RE: Thermal Expansion - Elastic and Plastic Deformation

(OP)
Thank you both for your prompt replies.

The component being heated is not constrained and is free to expand and is free of residual stresses.

Further to my original question, is there a temperature limit for any given material after which it will not return to it's original dimension once cooled again? If so, what is this temperature limit called?

I would like to try to find more information on this in books but I am unsure as to what to search for. The name of this temperature limit would definitely help. If anyone could provide me with any other topic names to search for please that would be very helpful too.

Many thanks,

Tom



RE: Thermal Expansion - Elastic and Plastic Deformation

The melting point. Once the material melts it will assume the shape of the container and will not return the the original shape upon cooling. If you want to see some really bizarre temperature behavior Google shape memory alloys.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

RE: Thermal Expansion - Elastic and Plastic Deformation

Changes in crystal structure or grain size may also cause irreversable dimensional changes. Every material will have its own unique behavior in this respect.

RE: Thermal Expansion - Elastic and Plastic Deformation

If the heating is slow enough to be really uniform then stress due to thermal expansion is pretty minimal.
But, I'd say if there are residual stresses in the part (for any of several possible causes including cold work or welding) then an excursion past 400 F or so will bring on a certain amount of stress relief due to temporary lowered yield strength and possibility of distortion. The higher the temp and longer the time at the max temp the greater the stress relief.
see page 3 here
http://www.gietech.be/LinkClick.aspx?fileticket=vd...;

RE: Thermal Expansion - Elastic and Plastic Deformation

(OP)
Excellent, thank you all for your help on this.

Yes I was referring to a change before the melting point is reached and melting of the metal occurs.

It is this change in crystal structure and grain size that I need to look into further for the metal in question. I will also look into relieving of residual stresses as this seems to be a related topic. Thanks Tmoose for the link.

Once again thanks very much for taking the time to give me a hand.

Tom

RE: Thermal Expansion - Elastic and Plastic Deformation

A while back I designed a Weld Jig for an Assy and the shop came back and asked if they could use it to anneal and heat treat while it was still in the Jig.
Without thinking I said ok. Now that is the last Assy that jig can be used for because it all shrunk.
I would guess you get my point about material and temperature.
By the way the material was 17-4 PH


Cheers

I don't know anything but the people that do.

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