Elastomer on top of a bending beam

[Nefertiti]

I'm trying to understand differences between two setups. In one setup I put a thin metal layer on top of a rigid plastic film, which I then bend to a certain radius. The metal is not very prone to crack in itself but with very small bending radius you are able to crack the surface.

If I have rigid plastic film which I then coat with elastomer, and put the thin metal layer on top of the elastomer, I generally get more cracks with given bending radius. If the thickness of these two setups is the same, the bending strain should also be the same. Why then I get more surface cracking with the elastomer than without it?

 

[JRMichler]

What you have is a bending beam problem, where the beam is composed of two or more materials. The procedure for analyzing should be in any basic mechanics of materials book. You first find the neutral axis for each setup. It's not in the middle because you have materials of different modulus of elasticity. Then you calculate the distance of the metal from the neutral axis for each setup. The strain for a given bend radius is proportional to the distance from the neutral axis. I expect you will find that the material coated with elastomer will have the metai farther from the neutral axis, thus larger strain. But that's just a SWAG, so please calculate and let us know what you find.

 

[Nidum]

Tell us more about the actual construction , materials , dimensions and loading ?