Why Does Heated Wire Remain Elongated After Cooling?

[130mikep]

thermal expansion of wire??

hi I've got this 3mm iron-chromium-aluminium wire fixed at both ends, heated to approx 1000k (max 1200K) and suspended horizontally approx 1metre long.

the wire it would appear has been extended by about 8mm, similar to what would be expected when its hot, only it stays this long when brought back down to room temperature!

so my question is: why?! lol

could it really be creep?

thanks, mike

 

[Dr_Morbius]

The wire probably stretched while it was hot and sagging down. If the wire stretched then it must also have gotten thinner.

 

[viscaritatis]

Was it fixed under significant tension? If it was, then yes, it could be creep.

Otherwise, it may depend on how it was cooled.

 

[Enthalpy]

Creeping is absolutely normal for steel at 1000K, much more at 1200K. Even over a short time with a moderate load.

Then, if your wire was new, you can have glowed it from some initial metallurgical state, like cold drawn. To decide what effect it was, just observe if the wire creeps further next time.

 

[alphy]

Thermal expansion is a well-known phenomenon in materials science, where objects expand or contract in response to changes in temperature. In the case of your wire, the increase in length when heated is due to thermal expansion. This is a result of the atoms in the wire vibrating more rapidly as the temperature increases, causing them to take up more space and resulting in the wire appearing longer. This is a normal behavior for most materials and is a well-studied phenomenon.

However, in your case, you have noticed that the wire remains elongated even when it is brought back to room temperature. This is where the concept of creep comes into play. Creep is a phenomenon where a material deforms over time under a constant load, even at room temperature. This can occur in materials that are subject to high temperatures or constant stress over a long period of time.

In your situation, it is possible that the combination of high temperature and the weight of the wire itself caused it to undergo creep, resulting in the permanent elongation you observed. This is a common occurrence in materials used in high-temperature applications, such as in aerospace or power generation industries.

In order to confirm if creep is the cause of the permanent elongation in your wire, further testing and analysis would be required. This could include measuring the creep behavior of the wire under different temperatures and loads, as well as examining the microstructure of the wire to see if any changes have occurred.

Overall, the thermal expansion and creep behavior of materials are important considerations for scientists and engineers in various industries. Understanding these phenomena can help us design and use materials more effectively in different applications.