Equilibrium of inverted shell of varying thickness
Equilibrium of inverted shell of varying thickness
(OP)
Hi,
I am doing FEM (Marc) of soft contact lenses simulating the inside out flipping of such lenses. While my FE results compare very well to measurements, I am having trouble to find literature about why the lens settles in a particular state.
The geometry of the soft contact lenses is not spherical, indeed the lens has a centre thickness of around 0.1 mm and the thickness varies along its diameter between 0.1 and 0.25 mm. Lens diameter is ~14mm and the lenses are made of silicone hydrogel materials, for my analysis I am assuming linear elasticity with M =~1 MPa. See attached for a sequence of the lens inversion.
Is there someone who can shine some light on why the lens assumes a specific shape when its flipped?
thanks loads in advance!
I am doing FEM (Marc) of soft contact lenses simulating the inside out flipping of such lenses. While my FE results compare very well to measurements, I am having trouble to find literature about why the lens settles in a particular state.
The geometry of the soft contact lenses is not spherical, indeed the lens has a centre thickness of around 0.1 mm and the thickness varies along its diameter between 0.1 and 0.25 mm. Lens diameter is ~14mm and the lenses are made of silicone hydrogel materials, for my analysis I am assuming linear elasticity with M =~1 MPa. See attached for a sequence of the lens inversion.
Is there someone who can shine some light on why the lens assumes a specific shape when its flipped?
thanks loads in advance!





RE: Equilibrium of inverted shell of varying thickness
RE: Equilibrium of inverted shell of varying thickness
RE: Equilibrium of inverted shell of varying thickness
As applied to the contact lens, I would say that the flipped version has almost no stretching/compressing of the middle surface, which would imply the middle surface is the mirror image of the unflipped one.
RE: Equilibrium of inverted shell of varying thickness
RE: Equilibrium of inverted shell of varying thickness
RE: Equilibrium of inverted shell of varying thickness
RE: Equilibrium of inverted shell of varying thickness
How about Timoshenko, Theory of Elastic Stability
or
http://en.wikipedia.org/wiki/Buckling
see the section headed "Energy Method"
RE: Equilibrium of inverted shell of varying thickness
RE: Equilibrium of inverted shell of varying thickness
perhaps there's something relative in how a small kids' toy that you purposely turned "inside out", then set it on a flat surface. It pops back into the original shape in a few (maybe 5 or 10) seconds.
Its initial shape was a hollow hemishere. The shape when inverted was quite different than its normal or relaxed state, but still a "constant profile" which looked like a miniature cooking kettle; the difference due to inner/outer surface areas being forced to change; which neither liked, and it popped back. The material was some tough rubbery substance akin to urethane. (maybe it was)
The toy was about 2 or 2 1/2" diameter, and of constant thickness (maybe 3/16 or 1/4") in the normal state as near as the eye could tell.
This may provide a little insight into why a lens of variable thickness takes on a non-constant shape