Fastener Single Shear Allowable Knockdowns

[mathlete7]

Hi,
I've always been under the impression that for single shear details that aren't stabilized by some other feature (loading causes rotation of the joint) the shear allowable of the fastener is reduced from the standard, "1/2 of the double-shear strength value". For instance, this is reflected in Table 8.1.2.1(b) of MMPDS (Mil-hdbk-5) which provides shear strength knockdown factors for rivets as a function of sheet thickness.
MMPDS doesn't have a table like this for bolts however (it does have joint strength tables as a function of member thickness). Maybe this question is academic if you have a joint strength table anyways, however would the fastener shear strength vary with sheet thickness for standard fasteners like it does with rivets? In the MMPDS joint strength tables it doesn't indicate what the failure mode is for the allowables provided (bearing vs shear) so you can't tell if the fastener shear strength is decreased for the lower sheet thicknesses or if the joint is just failing in bearing at the lower sheet thickness values.

Thanks much for any input...

 

[SWComposites]

"would the fastener shear strength vary with sheet thickness for standard fasteners like it does with rivets?"

Yes, the "appenent" or "in-situ" fastener strength will vary. Its not really correct to say the "shear" strength varies.

And yes, a major problem with the MMPDS joint strength tables is that they do not list the failure modes.

SW

 

[rb1957]

there are a couple of different things happening ...

for plain rivets you're seeing mostly bearing failures for thin sheets,
for CSK rivets you're also getting some effect from the CSK (a reduction in the bearing allowable, maybe a concentration at the root of the CSK)

will'll be able to tell us more ...