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joint stength tables
3

joint stength tables

joint stength tables

(OP)
I'd like to do a survey to find out what published tables are available for aircraft fastener joint strengths.  We typically use MIL-HDBK-5H and Boeing SRM tables for proven (tested) values for rivets, Hi-Loks, screws, etc. However, I often come across combinations of fastener/sheet materials for which I can find no published test values.  Part of the problem lies with working on older aircraft, but there must be other data available somewhere.  

RE: joint stength tables

There is one very good reason for not seeing joint allowables for other fastener and sheet thicknesses. The strength of a joint is highly dependent on the fastening process, there are so many variables in process alone that very few of the parameters can be treated analytically. To name a few, material of both fastener and sheet, the shape of the countersink, grip length of the fastener, faying surface treatment, precision of hole drilling, hole-filling fasterners (like rivets) vs bolt or screw type, cold-working of holes, manufacturing process of the fastener (machined thread, rolled thread, heat treated, how the head is "upset"), etc.

For this reason nearly all of the data in joint allowables tables are derived from many, many structural tests (at least 100 specimens for "B" basis allowables). These tests cost lots of money and few companies (especially OEM's) are going to give the data away.

What can even be worse is that a process specification may result in a joint with bad attributes that are discovered much later (after real-life experience). This will result in that process being changed and possibly all of the allowables becoming worthless.

You will also find very little data on joint stiffness (useful for structural analysis) for much the same reason.

Signed SamX,

former author of Boeing Design Manual sections on fastener allowables and joint allowables. Life can be so non-linear.

RE: joint stength tables

Samx,

Please subscribe to this forum..you are a valuable asset to this community..  :)

thx,

Inertia

-----
Nert

RE: joint stength tables

Hi Brin,
It would be nice if U could tell me how to access Boeing data on net. I too need some data like you for my repair work.

Appanna

RE: joint stength tables

(OP)
Appanna

-I don't think there is public (internet) access to Boeing data.  We use Boeing supplied repair manuals in .pdf (acrobat) form and also use myboeingfleet.com (paid).  

Otherwise, MIL-HDBK-5H is available on stinet http://stinet.dtic.mil/.

good luck,

Brin

RE: joint stength tables

MIL-HDBK-5H gives values for NAS1097-E rivets in 2024-T3 sheet, but not NAS1097-AD rivets.  Is it acceptable to apply the ratio of the Fsu values (41:26) to the values in the table?  If there are published values for the NAS1097-AD rivet, please let me know.

RE: joint stength tables

The bearing strength of the joint depends on the bearing allowable of the sheet. So, the values remain the same for 'E' as well as 'AD' rivets. Basically, you can use Table 8.1.2.1(a) of MIL-HDBK-5H factoring the values by the Fbru of 2024-T3 sheet.
However, the limiting load, which is the shear capability of the rivet stem depends on the Fsu of the rivet material.

RE: joint stength tables

(OP)
That would be OK for protruding head rivets, but the NAS1097 countersunk values are different.  

I haven't seen values for NAS1097AD rivets.  The B727 SRM lists values for "D" shear head rivets (BACR15CE-D) but that won't help you.  Anybody else?

On ratio'ng the shear values, it would depend on how critical your structure is and how conservative your numbers are.  But I wouldn't call it standard practice, and it would be difficult to defend this assumption under scrutiny.  Interpolating using Fsu ratio also does not consider rivet failure at the head (eg: head tearing off).

Can you use the MS20426AD joint strength values and call them conservative?  Or maybe simpler to use NAS1097E or DD rivets instead of trying to substantiate a lower strength rivet?
  
good luck

RE: joint stength tables

I have seen strength allowable data for NAS1097AD rivets in the Sabreliner Structural Repair Manual.  That is what I use for my data substantiation.
This manual also has a lot of data that is no longer published, such as the 7178 aluminum alloy.

RE: joint stength tables

The FFA in USA has the "RAPID" program the does an analysis of air craft structures and skin.  It can be downloaded for free. Hope it helps.

RE: joint stength tables

(OP)
can you provide a link for rapid?

thanks

RE: joint stength tables

RAPID does not have AD rivets as a selection.
The only rivet selection you can make in the RAPID database are E rivets.

RE: joint stength tables

FYI

BACR15CExxx = NAS1097xxx

RE: joint stength tables

A further short remark:
All joint allowables used in the analysis of aircraft structure in the USA have to be FAA approved data. The only official publicly published data are in Mil-HDBK-5. Allowable data used within the various aircraft companies have to be of the same or lower value and be certified by the FAA. FAA DER's (FAA Designated Engineering Representaves) are NOT allowed to approve fastener strength data ! I am a FAA DER.
This only for clarification.

Greetings Fritz-Gunther

RE: joint stength tables

gunther... Soooo...

  If You were presented with fastener test data, conducted by a Vendor, or independent test-lab, to MIL-HDBK-5 standards... BUT the data was NOT actually IN MIL-HDBK-5... You could not use that test data for fastener allowables???
Does all fastener-allowable data have to be approved by the FAA before use, on a type-certificated acft????

Regards, Wil Taylor

RE: joint stength tables

wktaylor:

Only FAA approved fastener allowables can be used in certification of US A/C.
All material and fastener test data must be referred to FAA for approval as specified in FAA Order 8110.49 (DER Handbook) but FAA may issue authorization letter to find compliance !
Therefore it is important to find out if published allowables are just test data, reduced as described in MIL-HDBK-5 to "B" or "A", or FAA approved allowables. See FAR 25.613 for description of allowables etc.
regards, F.G Hempel

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