[Boondocksaint]

Hey.

So, I have a few questions.

Lets say that I have a 3-layer laminte, consisiting of a fixed wall (W), an adhesive (A) and a small object (O) attached to the adhesive.

___________
                     |  ___   __
                     |  |   |   |  |
     Wall         |  | A|   |O|
                     |  |__|  |__|
                     |   
__________|


Say that these 3 layers have the following stats (all made up)

Wall: TEC= 1, H20=5%, L=2mm
Adhesive: TEC= 3, H20= 10%, L=0.5mm
Object: TEC= 2, H20 = 15%, L= 1mm

where
TEC= Thermal expansion coefficient (C^-1)
H20= Water absorbtion (%)
L= Lenght.


So my question is...

how do i calculate tensions created due to this?

Do i have to calculate tensions in all 3 layers? Should i add them together?
Or, should i rather calculate tensions in the interesting layer, the adhesive?

Also - since the wall is fixed i guess its change in lenght will be (TEC * L) /2. Correct?

Lastly - the wall is fixed, whereas the others isn't. Can someone explain what influence this will have?

[curiouscat]

I am confused:

1. To calculate the thermal stress don't you need to specify the temperature change?

2. Where does the H2O % enter these calculations?

[Boondocksaint]

Ah, my bad. I forgot.

1. Lets assume a temperature range of -50 to +50 degrees celsius.



2. Forgot to mention this also. The volume of the layers will expand due to humidity in the air.

This gives birth to a new question:

If the humidity is 50%, and a material absorbs up to 5%... that still mean that the material will get "saturated" (expanding full 5%), correct?

[curiouscat]

I think your question is a little too hypothetical / ambigious:

50% relative humidity or absolute? Material absorbs 5% of it's own weight? How much does it expand per % of H2O absorbed?

It would help if you told us what you are thinking about? What's the context?

[Boondocksaint]

Ah.

ok, so this is the application;

A thin polymerfilm is the to be fastened with an adhesive on a metal box (which is fixed).

This is to be places inside a building, and before that stored outside, with a variance of temperatures of about 100 degrees, with equal distribuion on both sides of 0 degrees (-50 to +50). When the  box is put into commision inside, the temperature is supposed to be constant, +50 degrees. Humidity is supposed to be 50%.

What I need to calculate is how the materials different Thermal expansion and water absorbation affects the adhesives performance over time. Therefore, I think I need to determine the stress, and most likely if fatigue may cause the adhesive to give up.

Normally  this would probably be an uneccesary calculation to perform, but since the polymerfilm is supposed to last for decades, I assume it's worth taking into consideration.

I hope this descibes the situation enough. Im horrible at chemistry.

[curiouscat]

By L do you really mean length or thickness?