Originally Posted by clevtool
The dimples in this cutaway do not look as crisp as what I would expect from properly formed dimples with good quality dies.
Agree. Not enough die pressure on the bottom sheet, in this case a rib flange. But that's a distraction, an aside to the real issue.
The focus here is on the oversize dimple immediately under the rivet head, 0.007" deeper and 0.0167" wider at the major diameter. Assume it to be perfectly formed as would be the case with a Cleaveland die and a skilled operator. Let's assume the use of a substructure dimple (0.011" deeper) and perfect nesting. Further assume the rivet head neither bent or cracked, and illustrations of such are mere anomalies. As intended, the tank die would result in a space under the rivet head. The space would, in theory, be filled with sealant.
Being rubber, the sealant would be roughly 10,000 times less stiff than aluminum (10,000,000/1,000). In the context of structure the rubber contributes only a tiny bit more than nothing
, or about the same as air.
So, consider this question: Having purposely left a space under the rivet head, what happens when a structural load is applied to the joint?