Maximum Edge Distance

[J_Souza]

Hello, everyone.

Is there a *maximum* fastener edge distance/margin -- and why?

Thanks!

 

[Sparweb]

The "maximum" edge distance occurs when a single fastener is installed through the middle of two infinite sheets of aluminum. Hence ED=infinite.

What would be the point?

STF

 

[rb1957]

why do you think there should be a maximum limit for eD ? what do you see degrading as eD increases ? I guess there are typical designs, I don't think I've seen eD > 3; why would you want a high eD ??

another day in paradise, or is paradise one day closer ?

 

[MintJulep]

I guess it sort of depends.

Edge of what?

 

[SAITAETGrad]

Of course - "it depends".

[edit: didn't see your post from five minutes before.]

Yes, you don't want your edges coming away & creating excessive gaps. This is less a concern with flat surfaces, thicker elements & larger fastener heads.

Some SRMs specify edge distance limits as a range. If you are laying out your edges for somewhere in 2.2 to 2.5 x diameter range with production tolerances, you shouldn't have any problems.

But horses for courses... How loaded is the structure? What are the impacts on inspectability?

Has anybody had that experience where a tech took it upon themselves to 're-design' a cover plate because your layout on a nutplate rivet was only 1.5D?

Rules of thumb are great - but not always the full picture.

 

[J_Souza]

As SAITAETGrad mentioned,
"Yes, you don't want your edges coming away & creating excessive gaps."

I may have seen "as built" repairs in which the std 2D+0.06 edge margin looked a lot more like 3~4D to me... so it got me thinking if this extra material beyond the critical row would not be detrimental to the assy??

 

[rb1957]

this condition would have been bought off by inspection if the dim'n was (as typically) minimum eD = 2. Although if it was hard dim'ned, as say 0.40", then normal drawing tolerances would apply +- 0.03", which would make 4D unacceptable without MRB/RNC/NCR/...

extra edge distance on a dblr is not detrimental, except as unnecessary weight, indeed there can be sensible reasons for this condition, like a frame rivet being out of line with the stringer rivets and the edge of the doubler being determined by the stringer rivets.

another day in paradise, or is paradise one day closer ?

 

[Sparweb]

I guess we need more context to give you a more specific answer JSouza. Just asking about "edge distance" in general can lead to all sorts of ideas about the configuration of the joint you may or may not be looking at.

Excess ED on a long skin joint, measured from the centerline of the row to the edge of the sheet would be a waste of material and add weight, and if taken to extremes could allow the edge of the sheet to be "peeled up". On the other hand, there is also an ED to be measured at the END rivet of the row, to the other edge of the sheet, and if this distance is excessive, then not only could this corner be lifted up, but the cross section around the unattached area will be unstressed by skin forces, while sheet in the area of the rivets will be, leading to a greater propensity for the corner to lift.

But I could be inventing an example that is different from the case you're interested in, J.

STF