Mininum thickness of skins to use countersink rivets
Mininum thickness of skins to use countersink rivets
(OP)
Hello. There must be a minimun number for the thickness.
Have searched online and the MIL-HDBK-5H, found nothing.
Pleae help.
Have searched online and the MIL-HDBK-5H, found nothing.
Pleae help.





RE: Mininum thickness of skins to use countersink rivets
The answer may be very dimple
RE: Mininum thickness of skins to use countersink rivets
When applying countersunk rivets, you'll want at least 0.2mm of the rivet's shaft standing. This is for keeping a proper allowable shear load.
When you know the height of the rivethead, you know the minimum thickness.
When the present thickness is lower than that, you may want to use countersunk rivets with a low head or apply dimpling like Zapster already mentioned.
You may also want to take a look at Bruhn, Section D1.18 - D1.22.
Good luck
RE: Mininum thickness of skins to use countersink rivets
RE: Mininum thickness of skins to use countersink rivets
Airbus will tell you that you require a minimum cylindrical portion of 0,4 mm in the sheet. For example a 4 mm dia NAS 1097 has a head height of about 1,0 mm, so the minimum skin thickness is 1,4 for that fastener.
A cylindrical portion of 0,2 mm will reduce the fatigue life by 25%
(ref A300 RAG)
RE: Mininum thickness of skins to use countersink rivets
RE: Mininum thickness of skins to use countersink rivets
RE: Mininum thickness of skins to use countersink rivets
What is the rivet/sheet configuration that concerns you?
Steven Fahey, CET
RE: Mininum thickness of skins to use countersink rivets
SparWeb: What is the rivet/sheet configuration that concerns you?
It is to rivet the wingskin to spar caps and rib caps. And I do care about the wing's aerodynamics... But at the wing tip, 0.025" skin is used for weight considerations. That's my situation.
RE: Mininum thickness of skins to use countersink rivets
1) live with the knife condition ... it is a wing tip, so you can expect it to be quite lightly loaded,
2) add an extra thickness on the rivet line ... quite commonly done, machining from a thicker plate, bonding (hot bonding preferred) doubler strips,
3) dimpling the skin ... a bit of a past practice (done many years ago to save the complexity of drilling a CSK).
a fatigue test would validate the design; conservative calcs too.
RE: Mininum thickness of skins to use countersink rivets
A) Chapter 7.1 General design considerations (of fasteners and structural joints)
B) Chapter 7.7 Fatigue design considerations - especially Figure 7.7.3 (page 232) and other references.
RE: Mininum thickness of skins to use countersink rivets
RE: Mininum thickness of skins to use countersink rivets
“As a general rule, use the drill countersink method when the thickness of the material is greater than the thickness of the rivet head, and use the dimpling method on thinner material. Figure 5-47 illustrates general rules for countersinking. Note in figure 5-47A that the material is quite thick and the head of the countersunk rivet extends only about halfway through the upper layer of metal. Countersinking will leave plenty of material for gripping.
In figure 5-47B the countersunk head reaches completely through the upper layer. this condition is permissible but should be avoided.
In figure 5-47C, the head extends well into the second layer of material. This indicates that the material is thin and that most of it would be ground away by drill countersinking; therefore, dimpling is preferred. Dimpling will work best if the material is not over 0.040-in. thick.”
Another good reference AC is AC 43.13-1B Acceptable Methods, Techniques, And Practices—Aircraft Inspection And Repair, Chapter 4. Metal Structure, Welding, and Brazing, Section 4 references back to MIL-HDBK-5 for hole sizes.
The above AC’s is available on the FAA web site at: http://www.faa.gov search under the AC and type in 65-15 or 43.13-1B and are great reference books.