A fillet is the cove of adhesive formed where squeeze-out meets the outside of the joint. Leaving a neat fillet instead of wiping it flat lowers peel stress at the overlap ends and can raise lap-joint strength noticeably. Fillets also seal the joint edge against moisture. On anaerobic and UV systems, the exposed fillet may need its own cure step.
Don't wipe the fillet off, tool it to a nice radius, that's what's holding the edge down.
Also heard as
- adhesive fillet
- spew fillet
Related terms
Squeeze-out
The excess adhesive that oozes out along the joint edges at clamp-up, read as proof the joint is full.
Peel stress
Tension pulling one adherend away from the other at the edge of a bond, concentrated along a thin line.
Lap joint
A bonded joint where two parts overlap face to face, loading the adhesive mainly in shear.
Oxygen inhibition
Air at the surface blocking the cure of free-radical adhesives, leaving them sticky where exposed.