Stress/Strain of Nylon 6,6

[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!!

 

[patprimmer]

I think you have missed a few significant points that may complicate the issue.

Std unfilled nylon has something like 10 times the rate of thermal expansion as steel, so the interface will be substantially effected.

Nylon 66 absorbs water from the environment and softens and expands considerably. From memory, about 1% expansion from dry as moulded to typical atmospheric conditions or about 3% from dry as moulded to submerged in water at room temperature.

There are many grades of nylon 5.6 available.

They may be unfilled with additives that effect the crystal structure. This can have a small impact on the properties that may concern you. It can be due to something as simple as a different colout formuation.

They may be filled or reinforced with minerals or glass fibre or even carbon or SS fibre. These can have a substantial or even dramatic effect on the properties than may be of interest to you.

All thermoplastics, including nylon creep under load, so you need stress/strain/time curves to properly analyze the design.

The stress/strain/time curves are strongly impacted by oisture level and temperature.

The interference fit will reduce over time due to all the above.

Regards
Pat
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[Vig16]

Yes,I forgot to include that the Nylon 66 is 33% glass filled. I knew I'd forget things from my description.

Would the 33% glass fill have an effect on my calculations?

 

[patprimmer]

33% glass fibre will have a VERY substantial effect on your calculations and it is anisotropic as the reinforcement is much greater in direction of fibre orientation which is dependent on flow direction as the mould fills.

Regards
Pat
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