Which Bearing Allowable for Countersunk Fastener
Which Bearing Allowable for Countersunk Fastener
(OP)
Dears,
I know that this topic has been appraoched several times through many named threads but there is still some confusion (to me) on the subject...I would like to know if anyone is used to following bearing allowable stress: Sbr=Fsu/(d*(t-0.5*CSK)
where t is the sheet thickness, d is the fastener diameter, CSK is the Coutersink Heigth.
Actually I have seen this formula a long time ago but I can not remember where exactly (reference)?
Thank you in advance and best regards,
I know that this topic has been appraoched several times through many named threads but there is still some confusion (to me) on the subject...I would like to know if anyone is used to following bearing allowable stress: Sbr=Fsu/(d*(t-0.5*CSK)
where t is the sheet thickness, d is the fastener diameter, CSK is the Coutersink Heigth.
Actually I have seen this formula a long time ago but I can not remember where exactly (reference)?
Thank you in advance and best regards,





RE: Which Bearing Allowable for Countersunk Fastener
RE: Which Bearing Allowable for Countersunk Fastener
but i wouldn't make an allowable bearing stress out of an allowable shear load (i think your allowable is way too low).
you Could do Fbr = Sbru*(d*(t-0.5*CSK)), which says that the CK is not fully effective in bearing.
why aren't you using the tables in MIL-HDBK 5 ?
RE: Which Bearing Allowable for Countersunk Fastener
@rb1957: Actually, the most (may be all) of the shear load is transferred based on the "vertical" part of the rivet shank (also for shear area: pi*d^4/4, d is the diameter of the rivet shank). The reason whey only one half of the thickness has been considered in the above formula. This seems more physical/realistic to me!
To my knowledge tables from MIL-HDBK 5 are dedicated to protruding rivets.
htt
@I-B-62
Rgd.
RE: Which Bearing Allowable for Countersunk Fastener
my post was concerned with calculating a bearing allowable stress based shear allowable load ...
pi*d^4/4 is something, but it isn't the area of anything.
MIL-HDBK 5 considers many types of rivets, the tables are most useful for CSK rivets (since it is pretty easy to calculate allowables for protruding head rivets, being Fbru*d*t).
your equation as written doesn't match your reference.
i'm really surprised that if you're working on a airplane why are you using what looks like a civil (building) code. if you aren't working on an airplane, please post in the right forum, maybe "structural engineering".
RE: Which Bearing Allowable for Countersunk Fastener
The large airframers will use proprietary allowables developed from their own tests as well as Mil5 data. I would advise caution when applying the formula you have found without test data to support it. It may be conservative for one application and un-conservative in another.
RE: Which Bearing Allowable for Countersunk Fastener
As Specialmission said, "The large airframers will use proprietary allowables developed from their own tests as well as Mil5 data."
But from the limited aerospace companies I've worked for I've never seen a reduction factor less than 50% of the csk thickness (based on 66%-70% csk depth). They were mostly around 70% (+/-5%) of the protruding head fastener based on Tension of Shear Head (obviously Tension Head Csk having a lower allowable then Shear Head in Bearing).
Anyhow...good luck. My advice is to use Mil-HDBK-5 or your specific company allowables.
I would not use the Psu allowables because they are different failure modes.