Does a MS20426DD rivet can be replaced by a MS20426AD rivet 5

[Cisnerjo]

Can someone please help me on this, can a MS20426DD rivet can be substituted by a MS20426AD rivet, I search on the National Aerospace Standards and it tells me that the DD or D rivets are inactive for new design, does anyboy know what would be a good substitute?.

Thanks for your time.

Regards!

 

[rb1957]

NO ... DD rivets are stronger than AD ...
check chapter 8 in Mil-Hdbk 5 (or AR-MMPDS-01)

DD can be substituted by E or ND

 

[WKTaylor]

rb1957... is exactly correct!

"AD" [2117-T4] "D" [2017-T4] and "DD" [2024-T4] are definitely not the same.

D and DD rivets have a version [anodized finish ONLY] that can be heat treated and quenched... then be driven [shot] in the "W" temper. Freezing these rivets immediately after quenching will preserve the W temper for a short while, allowing them to be driven at a later date. but BE CAREFUL... they are time-out-of quench sensitive. When they age harden in-place they assume the -T42 temper.

D rivets can be driven "hard" [in the -T3 temper] without cracking... but they are very tough to drive much larger than 3/16-Dia [a good reason for shooting larger rivets in the "W" temper]. Larger D rivets can be mechanically squeezed with care. NOTE: D rivets can have a chemical conversion coating [CCC] or anodized finish: DO NOT HEAT TREAT the CCC rivets: You will destroy the CCC finish [anodize finish will survive HT just fine]!!!

The "E" [7050-T73] rivet is not easy to drive "hard" [as heat treated]... but will match/exceed the strength of the D and DD rivets driven "ice-box".

Note: the D and DD rivets may be labeled "inactive for new design"... but that doesn't mean they are unavailable! CHECK!!!! Lots of older acft use these rivets!

Note: in-a pinch, I have substituted one larger diameter AD [typically 1/32] rivet for a D or DD rivet [SMALLER DIAS ONLY]. In this case they have roughly the same installed strength

CAUTION: check the static shear ultimate numbers first in MMPDS or a corporate design manual FIRST. For odd-oversize driven rivets [Example: NAS1241, NAS1242] You may have to estimate drilled hole size and then do P/A calculations to compare shear strength. P = driven shear strength [KSI] for the alloy. A = area of the rivet hole.

Regards, Wil Taylor

 

[edmeister]

Do not dismiss DD rivets as "inactive" from a different perspetive. For all repair Engineers who have to deal with daily issues such as mis-drilled holes or plug rivets. Note that DD rivets can be still be obtained in diameters upto 1/2" & in almost all lengths. They provide the perfect fix in unique situations where a "oversize" hole in thin skins has to be plugged (provided E.D. is ok). Using a large dia DD rivet - the most misdrilled situation can be rectified with a single fastener - in lieu of a repair doubler & associated DTA issues. After the heat treat (ice-box rivet) process - the rivet is very malable to install in the most difficult locations. (with utmost care not to buckle the web driving this fastener)- resultant savings found in eliminating a freeze plug install procedure; machining & cad-plating. (rivet shank is anodized - thus eliminating the plating requiremet) - No other fastener alloy provides such a malable condition for ease of installation. The crack growth from this larger dia fastener should in most cases be slower then the associated adjacent fasteners. This may not work for most repairs - but has some benefits as a field repair - or where machining or plating facilities are not available.

 

[rb1957]

ed,

i'm surprised you're using a DD to fill a hole. i'd be an AD (as i think they have better hole filling and less processing restrictions).

just my 2c

 

[berkshire]

rb1957
A DD in the AQ condition ( before the time limits expire) is softer than an AD rivet.
B.E.

 

[WKTaylor]

berkshire has a great point...

Up-to-about 3/16" or 7/32" Dia, most good mechanics can hand-drive "hard rivets". Squeeze equipment can drive larger "hard rivets" up-to about ~3/8" Dia no-sweat.

Rivets larger than these Dias should be driven in the "soft" W temper. I have heard mechanics describe installing these "soft" rivets like driving butter. "W" temper rivets up-to 3/8" Dia are generally easy to shoot by hand... and experienced mechanics can hand-shoot slightly larger sizes.

CAUTION.
I have heard mechanics say they are shooting "annealed" rivets which is entirely incorrect... the annealed temper [solution heat treated and air cooled] will not significantly harden after shooting [minor strain hardening only] and will have disastrous structural consequences.

2xxx alloy rivets properly solution heat treated and water-quenched "by the book"... and shot while in the [soft] "W" [post quench unstable] temper... will spontaneously age harden [in-place] to the -T42 temper and be very strong [MMPDS values]. Note: freezing after the quench [0F down to -40F] will grossly delay [or stop] the spontaneous age-hardening process and allow mechanics "working" time.

Regards, Wil Taylor