Strength of Solid vs. Blind Rivets

Hi all:

Quick question, I've been doing the math on the tensile and shear strength of various rivets and I noted that some minimum specs for rivets are in force and some are in pressure. Since pressure = force / area, I am thinking to convert the strengths of a LP4-3 from pounds to psi, I need to divide the quoted shear and tensile strength, by the area of the 1/8" diameter hole in this case. That would make the LP4-3 vs a comparable solid rivet about ~50.5% of solid rivet strength. Is that right? That's quite a difference.

Thanks.

Tyler

No rivet of any type should be utilized in tension. As the related analysis should be only shear, pressure makes sense as the load in bearing is the critical factor. Lots of other factors. There is a very wide degree of pull
rivets. Cherry lock and Cherry max have hardened steel cores. Still wouldn’t trust them in tension over a threaded fastener. A good example to look at are the heads of hi-lok fasteners. Protruding heads for tension apps. Stick with the first sentence here and stay safe.

There is also the friction between the layers with the "clamping force" of the rivet.

As a hypothetical example for a fictitious rivet. A set rivet imposes 100lbs of clamping force. That creates static friction between the layers of 50lbs. The rivet also has a shear strength of 200lbs. The strength of the individual rivet in the joint is 250lbs.

Some airplanes proseal every rivet joint to dramatically increase the shear strength of the joint beyond simply the rivets.

I'm no design engineer, so I have no idea what different engineers and designs take credit for.

Good points...

Thanks for the information and advice here. I was just surprised at how different they are! TR

I'll go a little further since I have a keyboard vs just my thumbs. Rivets are intended for shear applications. They are bucked (swelled) during installation for a ~ zero tolerance fit. This gets rid of any cyclic loading -> lowers fatigue risk. Large steel structures like bridges, ship hulls, buildings were riveted together long ago for similar reasons. Welding just wasn't refined yet

There are known, empirical/measured benefits to the zero tolerance fit (friction) and the rivet head (in tension). A bucked rivet is also strain hardened; thus, stronger than the virgin manufactured material., In general, the first two (and sometimes all) of the aforementioned properties become design margin versus intentional application. A case-in-point for intended application; many aircraft manufacturers utilize 1097 rivets fairly exclusively in their skins (Lear, modern Pipers, others IIRC). To the OP: if you're not familiar, look them up. Seemingly almost no head on them. I'm guessing this is to lower manufacturing cost by eliminating double dimpling or dimpling + countersink ops and doing a single CS in the skin. At least one of those manufacturers, probably several, utilizes thinner skins that are heat treated after forming to save weight. The point is; if any appreciable tension was present, you'd see a lot of popped heads.

I'll reference hi-loks and their reference, application material again as a good example.

Now back to the original question. Pull rivets cover a wide spectrum of properties. Like solid rivets, the installation should swell the body a bit (most tend to be pretty soft) but even the best ones don't match solid rivets in that regard.

Stick with the OEM listed properties for the fasteners and fastener call outs from the designer. If there's a tension component, use a threaded fastener.

Stay safe.

TylerTCF said:

Hi all:

Quick question, I've been doing the math on the tensile and shear strength of various rivets and I noted that some minimum specs for rivets are in force and some are in pressure. Since pressure = force / area, I am thinking to convert the strengths of a LP4-3 from pounds to psi, I need to divide the quoted shear and tensile strength, by the area of the 1/8" diameter hole in this case. That would make the LP4-3 vs a comparable solid rivet about ~50.5% of solid rivet strength. Is that right? That's quite a difference.

Thanks.

Tyler

Click to expand...

LP4's are aluminum IIRC. There are also monel and SS rivets that have much higher shear ratings. I vaguely remember vans saying that the BK319 (monel) is almost as strong as the the AD 3 rivets and could be substituted in most areas in small quantities.

FYI Pop Monel MK319BS

This rivet is a "Pop" product, and has a listed Typical Ultimate Strength of 258 lb in shear, and 292 lb in tension.

An AN426AD3-? has a given design allowance of 217 lb in shear, per MIL-HDBK-5F, for .032 dimpled sheet thickness. Replacing these rivets with the Monel Pop's will not significantly degrade the joint.

Point of Reference: (RV-3B) From Van's Builder's Manual -

OPTIONAL SKINNING PROCEDURE (Bottom Wing Skin)

Those who choose, may install the bottom wing skins using MK319BS (Monel) blind rivets.
Per Section 7 - Wing, Page 7-25

FYI but YYMV

HFS

Building RV-3B S/N 11226

Tell that to the guy trying to sell his pop rivet RV. If I saw LP4 pop rivets in place of a AD I'd walk away. Another thing not being mentioned is a solid rivet will fill the hole, a pop rivet will not and I doubt anyone is drilling dead straight close tolerance holes for pop rivets.
Also someone needs to call Boeing Engineering and tell them rivets should never be used in tension applications.
I have had enough of the internet experts on this forum, apparently farmers are more knowledgeable than I, I have only spent 45 years working in the industry.
Good luck with your builds, enjoy your planes. Goodbye.

There's two rivets in every RV-8 rear seat footwell area that are loaded entirely in tension.

Cherry Max Rivets are generally accepted to be stronger in shear than solid AD rivets.

To try and get this thread back in the right direction, LP4-3 rivets are pretty weak as compared to solid AD rivets. However Cherry Max are a different beast. There are other Cherry brand rivets that are significantly stronger than LP4-3 as well. It's impossible to make a blanket statement about "solid" vs "blind" rivets as there are way too many varieties of each. A "soft" AN4xxA- rivet will not be as strong as a Cherry Max. The various monel or stainless Cherry rivets may or may not be as strong.

Thanks everyone! I was really trying to grapple with the difference in strength between the rivets and to make sure any replacements are appropriately chosen. I was really surprised when the strength was 50%ish (in both directions) of the solid rivets for LP4-3s, so I started looking at other rivet brands/specs. Anyways, I appreciate everyone's thoughtful information and for providing great insight for those behind us. Build on!

RV-10 soon...

TR

One point I did not see mentioned is extolled by a Boeing Engineer on the Eng-Tips Forum.

Blind or pull rivets, if they're to achieve their rated capacity require a much more accurate hole tolerance, and, IIRC, superior to that typically achieved with a AD rivet.