Prevost XLII Skin Delamination Repair

[davidbrady]

Hi Hish,

Thanks for the info on the CherryMAX. It is indeed a very good blind rivet. You know this stuff Hish, but for the benefit of others who find this stuff interesting, we now need to consider the bearing shear strength of the hole in the stainless side panel. The strength of the bearing area is given by BearingYieldStrength*D*t. Where:

BearingYieldStrength = 1.5 TensileYieldStrength = 1.5*30000 = 45000 psi
D = diameter of the hole = 3/16 = 0.1875"
t = thickness of the thinnest sheet = 0.060"

Which gives a bear shear strength of (45000*0.1875*0.060) = 506 pounds, so using CherryMAX rivets has made the hole in the skin the limiting factor. Given a 3" rivet pitch we're limited to 506/3 = 169 lb/in of linear strength on the panel edge. Frankly, I'd rather have a rivet break than a panel break.

I'm still puzzled over why the H3 doesn't see the same issues as the XLII. After all the H3 is also bonding stainless steel. The H3 has a stainless space frame superstructure to which Prevost has bonded a fiberglass-reinforced polymer (FRP) side panel. Apparently the stainless bonding issues aren't a problem in the H3. Why?

I have a theory, It may have to do with exterior side panel buckling strength. I know on my H3 the FRP panels are only attached to the stainless space frame along the edges. The XLII attaches panels around the panel perimeter and also in the center of the panel. I wonder how the buckling strength compares between a Prevost FRP panel and a stainless steel panel. Of course, Prevost has complete control of the buckling stiffness of the stainless panel. They do this by adding stiffening ribs. I'm thinking the H3 FRP panels may have less buckling resistance and because they're not attached in the center they're allowed to buckle, however slight the buckle may be, it may be just enough to keep the glue stresses within its elastic region and down so low that stainless adhesive failure doesn't occur. I know... speculation, but still interesting. Thoughts?