At load levels that are well within the elastic load range, the shear stiffness is primarily determined by the fasteners and the dimples. Trapped sealant will act somewhat incompressibly, and I think that might give it significantly more shear stiffness than if it had free edges. It might be more significant than the 1/10,000 that Dan suggested, which is based upon the relative modulus of elasticity. Perhaps someone with more elastomer experience that I have might want to comment.
Thanks Dave. Two useful notes on sealant.
Mixed/cured sealant is a closed cell sponge, not a monolithic rubber block. The voids have two sources, air entrained in the mixing process and and to a lesser degree solvent vapor (mostly toluene). The solvent evaporates out during cure (much like the solvent in paint), leaving the voids.
This at 10x, best I can photograph in my shop. I'm told that at greater magnification you would see many more smaller voids
A rubber solid (just like hydraulic fluid) may in fact be relatively incompressible if fully encapsulated without the possibility of extrusion. That's not the case here. The air voids are compressible (like air bubbles in hydraulic fluid, to use the same example), and all parts of the joint are open at some edge.
In any event, there's probably normally enough shear stiffness in the design to prevent sealant failure
To prevent fay and fastener seal failure (but luckily not fillet seal failure) the joint would need to be very stiff indeed.
Here are typical measured results from a sealant qualification test:
The first column, tensile strength, is noteworthy because so many folks think of sealant as some kind of high strength adhesive.
The second column, percent elongation, is of specific interest here.
For this test sample freshly cured sealant never exposed to heat or hydrocarbons had an elongation of 460%. What it means in practical application is this; assume a joint with a 0.001" gap between two surfaces, said gap filled with sealant. When the joint is placed in shear, the sealant will suffer cohesive or adhesive failure at 0.0046" relative movement between the parts.
Note elongation values drop significantly after exposure to heat and hydrocarbons. The available joint elongation before sealant rupture has become very short.
One additional note. The "AMS 2629" fluid you see here is a standard test hydrocarbon which approximates jet fuel. You may be surprised to learn the standards for our sealant
do not include any requirement to test with gasoline.
As noted elsewhere, the blister database suggests both service time and elevated temperatures are required before blister formation.