Aluminium Expansion
Aluminium Expansion
(OP)
Hi, can someone please help me with how to calculate the expansion of aluminium with heat? I know the alloy will probably affect the result, but I'm just after a guide amount at this stage. For reference the piece in question is 65mm deep, and temperature change will be between circa 10degrees C and 100degrees C.
Thanks.
Thanks.





RE: Aluminium Expansion
I'd say a quick google will solve your question, as these thermal expansion coefficients (and formulae) are widely available on the web.
RE: Aluminium Expansion
http://ww
RE: Aluminium Expansion
Basically it is a big block of ally, with several holes going through one plane, which is 65mm thick, I just want to find out how much it will stretch a steel stud that passes through the hole when heated up, so I can look into whether the stud is operating in its elastic range.
Sorry if this all sounds so amateur, I haven't really done much of this since 2 years of it at college several years ago so I'm very rusty and really appreciate the help!
RE: Aluminium Expansion
Extension = original length * coeff lin exp * temp change
= 65mm * 23*10^-6* (100-10)= 0.13455mm or
about 0.005"
However if your bolt is subject to the same temperature change then the problems a little more complicated, because the aluminium won't expand by the amount above, what will actually happen is that the bolt will see some more tensile stress ie expand more than it wants to and the aluminium will be held in slight compression by the bolt preload, what you should check for is that the aluminium doesn't get over stressed during the expansion.
see this link:-
http://ww
desertfox
RE: Aluminium Expansion
RE: Aluminium Expansion
then how much the Al expands is less than 1/2 the problem; the steel stud will affect the result.
As others have said, google "thermal expansion coefficients" and you should be able to help yourself.
RE: Aluminium Expansion
I always try google before posting on here but the problem is getting few appropriate results and even then you often get different information and you dont know who has written it, hence why I trust the views of knowledgeable individuals on here more.
Thanks
RE: Aluminium Expansion
I'll try and pst an example of what your up against in the next few days.
desertfox
RE: Aluminium Expansion
RE: Aluminium Expansion
for 100 C the diff temp is 212 F and the strain on the bolt is .0000065*212= .00137. The stress on the bolt would be this * the modulus of elasticity or
E*.00137=30,000,000*.00137=41000 psi.
due to thermal expansion. You have to add the preload stress in the bolt to this to get the final value. Careful torqueing of the the bolt is necessary to get a handle on this value.
RE: Aluminium Expansion
deltaT = 100 °C = 180 °F
RE: Aluminium Expansion
RE: Aluminium Expansion
Yes
RE: Aluminium Expansion
RE: Aluminium Expansion
RE: Aluminium Expansion
RE: Aluminium Expansion
that was exactly my point
and Tomcannon
yes because you are taking account a temperature variation (deltaT)
A numerical example:
-) convert 100 °C to °F and you get 212 °F
-) convert 0 °C to °F and you get 32 °F
-)deltaT = 100°C - 0°C = 100 °C = 212 °F -32 °F =180 °F
RE: Aluminium Expansion
RE: Aluminium Expansion
I have uploaded a file which shows how to calculate the stresses purely due to the expansion of the bolt and aluminium, I assumed a bolt size of M10 based on your washer size of 0.75" OD and I used the washer area for the area of the aluminium subjected to the increased force.
Now to detemine whether your bolt or aluminium yields under the expansion we need to add the mechanical stresses of tightening the joint to those generated by the temperature rise.
So if you tighten your bolt to say 70% of yield and yield is 800N/mm^2 then bolt stress from tightening will be 0.7*800= 560 N/mm^2 and equal a bolt preload of about 63kN, now the stress under the washer in the aluminium will be 244N/mm^2 which in my opinion is high and you need to add another 38N/mm^2 to this figure giving a total stress 282N/mm^2 post expansion, your bolt meanwhile has an increased stress of 125N/mm^2 giving a total of 685N/mm^2 post expansion.
I would worry more about the aluminium embedding as opposed to the bolts stretching elastically.
RE: Aluminium Expansion
Regards,
Tom
RE: Aluminium Expansion
Your welcome, just remember thats just a rough example, it doesn't look at thread engagement etc, also it assumes that the joint as reached equilibrium temperature wise, I would advise you also to see how the yield stress changes with temperature for your materials as you will find it reduces as the temperature increases.
desertfox
RE: Aluminium Expansion
my 2c, i wouldn't react the preload under the washer (area), i'd use the bolt head area ... maybe not much in it.