Stress/Strain of Componets under Thermal expansion

[Vig16]

I'm trying to find the stress/strain relationship of a Cylindrical component (Nylon) when it has a carbon based Stainless Steel to help with conductivity. The SS piece is stationary during use as is the Nylon piece. The entire assembly has an SS cylinder around it which has a .002" interference as worst case condition based on a tolerance analysis. The assembly (a solenoid type assembly) undergoes a high temperature change during use (20 deg C - 80 deg C).

I'm drawing a blank as it's been so many years since I used any of my physics equations since college! Can any of you point me in the right direction on how to calculate how much stress/strain that the Nylon goes through with the thermal expansion over 60 deg C?

Thanks!!

 

[davefitz]

Check with a Timoshenko text- except for the 0.002" slip fit, the strain would be e=a*DT/ (1-p) , where e= strain in/in, a= thermal exp coeficient in / in F , DT = temperature change, p= poisson's ratio.

The stress would be simplly S= E*e, E= youngs modulus.

 

[zekeman]

Please post dimensions and better description of all components; your description is not clear.

If the thickness of nylon is small next to the diameter and is the outside jacket, I get

stress due to interference=En*.002/D
D= diameter of cylinder
En= modulus for nylon
For the thermal induced stress

stress= (a1-a2)*deltaT*En
a1=thermal expansion coeffficient steel,units 1/deg c
a2=thermal expansion coeffficient nylon


If the nylon thickness is not small then you have to post its thichness before a

 

[Vig16]

Sorry about not being clear in my description.

The OD of the Nylon piece is .340" with a wall thickness of .030"
The carbon based SS washer is .877" OD and ID .382"
The SS cylinder is .880" ID (which interfers with the SS washer)

I hope that gives a better idea of what it looks like. If not, ask me to better describe it again...

Thanks for all the replies!

 

[desertfox]

Hi Vig16

Reading your last post it appears that the only interference you have is between the stanless washers and stainless tube? I thought the interference was between the stainless and nylon pleae confirm.

desertfox

 

[Vig16]

If you're assuming there's no deformation of the Nylon, then you're correct; however, the Nylon is more susceptible to deformation than the SS cylinder or the washer, so that's why I placed the deformation between the Nylon and the washer.

Hope that clarifies my reasoning.

 

[Vig16]

I attached a picture (if I did it right) of the problem at hand. The green piece is the Nylon, the blue one is the washer, and the yellow one is the outer SS cylinder which shows the interference.

As of now I have this from davefitz for a formula to use for strain: e=a*DT/ (1-p) , where e= strain in/in, a= thermal exp coeficient in / in F , DT = temperature change, p= poisson's ratio.The stress would be simplly S= E*e, E= youngs modulus.

For stress I have two different equations, but I think since the Nylon is NOT the outside jacket and the SS cylinder is the outside jacket, I should probably use davefitz's equation.

Am I correct in that reasoning for which equations to use?

 

[desertfox]

Hi Vig16

The Nylon OD is given as 0.34" and the stainless steel ID you give as 0.881 ID so those components are clear of each other.
Also the SS washer ID is 0.382" also clearing the nylon cylinder, so how does the nylon become restrained by the stainless steel?

Regards

desertfox

 

[Vig16]

Well, I didn't include the tolerances, but the interference is at worst case situation. The tolerances are included in the picture I attached above to show the interference.