in general, bolt hole bearing stress=P/dt, where P=bolt load, d=bolt dia. t=matl thk regardless the hole is straight (protruding head bolt) or csk (countersunk head bolt). what if the hole is excessively chamfer/fillet relief so the result looks almost like csk hole, then what is t if protruding head bolt is used in csk hole, thk = matl thk - csk depth?
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protruding head bolt in csk hole bearing stress
- Thread starter namylem
- Start date
SWComposites
Aerospace
Fasteners have a radius between head and shank to reduce the Kt and avoid fastener failure. Most (maybe all) fastener heads are formed, not machined, another reason for the root radius. High strength bolts require high install torque levels therefore have high tensile preloads, therefore tend to have larger radii between head and shank; many of those fasteners require use of a countersunk washer under the head. Typical Ti Hiloks and similar are installed into holes with only a very small deburr of the hole edge; and in aluminum sheets the fasteners are typically installed with interference fits to improve the aluminum sheet fatigue strength.
namylem - you still haven’t answered all of the questions. Including, what is this joint for? Does it hold a number plate on, or does it attach a wing to the rest of the aircraft. A “bit” different criticality.
namylem - you still haven’t answered all of the questions. Including, what is this joint for? Does it hold a number plate on, or does it attach a wing to the rest of the aircraft. A “bit” different criticality.
- Thread starter
- #23
swc - plz refer to attached gfx in earlier post, it has most info you need. for sake of discussion, bolt is tension head nas bolt i will provide pic later but for now it is wing stab rib between spars, simple shear tab connection at both ends
SWComposites
Aerospace
so the connection is rib shear tab to spar web? (wouldn't make much sense for a protruding head bolt to be on a wing skin external surface).
so if connecting to the spar web, then likely the spar sees significant fatigue loads, so without further details I continue to say this condition is not acceptable. the "countersink" depth is almost 50% of sheet thickness. you have to not only check bearing stress with a reduced thickness, but you have to check fatigue in the aluminum sheet with a lack of hole fill and increased Kt at the hole. an acceptable "repair" might be to replace the fastener with a flush head bolt. a tapered washer "filler" might be acceptable if the washer is smaller diameter than the fastener head.
so if connecting to the spar web, then likely the spar sees significant fatigue loads, so without further details I continue to say this condition is not acceptable. the "countersink" depth is almost 50% of sheet thickness. you have to not only check bearing stress with a reduced thickness, but you have to check fatigue in the aluminum sheet with a lack of hole fill and increased Kt at the hole. an acceptable "repair" might be to replace the fastener with a flush head bolt. a tapered washer "filler" might be acceptable if the washer is smaller diameter than the fastener head.
- Thread starter
- #25
ok, see my reply back on the 17th (at 00:05) ... either
1) up-size the fastener to clean out the CSK (increasing the shank by 1/16" should be enough), or
2) use a CSK repair filler to "remove" the CSK (I think you should be familiar with CSK repairs, if you work in aerospace).
"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.
1) up-size the fastener to clean out the CSK (increasing the shank by 1/16" should be enough), or
2) use a CSK repair filler to "remove" the CSK (I think you should be familiar with CSK repairs, if you work in aerospace).
"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.
LiftDivergence
Aerospace
namylem said:
To be pedantic, this is true ONLY IF there is ZERO eccentricity in the joint, which is not usually the case.
Keep em' Flying
//Fight Corrosion!
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