strength of pop rivets v screws

[tonyjohnson]

Does anyone know the tensil and shear strengths of the following"

cs4-4 pop rivets

#4 stainless steel machine screws


I googled and checked all my reference materials but did not find that information.

Thanks in advance.

Tony

[GAHco]

Originally Posted by tonyjohnson

Does anyone know the tensil and shear strengths of the following"

cs4-4 pop rivets

#4 stainless steel machine screws


I googled and checked all my reference materials but did not find that information.

Thanks in advance.

Tony

4-40 machine screws are fully threaded, this disqualifies them from be a good shear fastener. The threads would be the bearing surface during shear loads.
Shear loads are best met with smooth round and tight fitting fasteners. Machine screws do not fit that definition. While it may be true that the material of the screw may have a higher shear value than the rivet, the rivet is better designed to do the job.

Is the installation calling for a rivet, or a machine screw?

Where are the fasteners going? (what structure are they going on?)

How much load is on the fastener.

Is there redundancy in the design?

Do you want easier access.

The simplest and most available high shear fasteners are Hi-Lok fasteners.

They have a close tolerance shank and low weight to strength ratio.

Pictures and Prices
http://www.gen-aircraft-hardware.com...187~187&id=187

Tech Info Pages
http://www.gen-aircraft-hardware.com.../pdf/hilok.pdf

Check them out, and get back with any more questions, I will post back as I have time.

[tonyjohnson]

Tom,

Thanks for your reply to this rather difficult question. I appreciate your pointing out that the threads would be taking the load and that another style of fastener would perhaps be better.

I am intending to install my canopy with sikaflex instead of the pop rivets that vans calls for in the plans. I would like to add redundancy by installing metal fasteners through the bond. I am told that those fasteners are known as "chicken fasteners" in the aerospace industry. They will go through through the fiberglass canopy skirt, the canopy, the sikaflex bond and the canopy frame. They will be secured with a nut on the interior of the aircraft at the canopy frame. I intend to countersink the fiberglass canopy skirt and glass over the fastener heads.

Do the hi lok fasteners come that small?

The smaller and stronger the better.

Can you recommend a fastener that meets that need?

Thanks,

Tony

[terrykohler]

4-40 machine screws are fully threaded, this disqualifies them from be a good shear fastener. The threads would be the bearing surface during shear loads.
Shear loads are best met with smooth round and tight fitting fasteners. Machine screws do not fit that definition. While it may be true that the material of the screw may have a higher shear value than the rivet, the rivet is better designed to do the job.

Bob:
Have to take issue with your statement. The important consideration is joint geometry and the ability of the fastener to meet the needs of that geometry. Without knowing the joint design,load or fastener application, its pretty pointless to know the shear and tensile strength of like diameter fasteners. For example, in the fastening of wheels on heavy trucks, virtually all studs are threaded full length. While these fastenerns have substantial shear strength, their function is to provide clamping force which in turn supports the load of the vehicle. If the clamp load is lost (loose nuts) and joint loading becomes shear, the studs will fracture and the wheel(s) will come off.
Typically, a joint utilizing torque or axial force on the fasteners is attempting to engage the geometry or friction of the mating surfaces to support the load. Think of the male fastener as a rubber band. The further it is stretched without breaking, the more clamp load it provides. This is why torque angle rather than torque loading (pound-feet) is the preferred method of maximizing clamp force. Angle, or linear distance up the thread helix, is a more accurate method of getting the desired stretch. Blind rivets also take advantage of a target clamping force by virtue of the load required to fracture the pin during setting. Shear strength of such fasteners is typically of secondary importance.
Terry
RV9A
N323TP

[GAHco]

Originally Posted by terrykohler

4-40 machine screws are fully threaded, this disqualifies them from be a good shear fastener. The threads would be the bearing surface during shear loads.
Shear loads are best met with smooth round and tight fitting fasteners. Machine screws do not fit that definition. While it may be true that the material of the screw may have a higher shear value than the rivet, the rivet is better designed to do the job.

Bob:
Have to take issue with your statement. The important consideration is joint geometry and the ability of the fastener to meet the needs of that geometry. Without knowing the joint design, load or fastener application, its pretty pointless to know the shear and tensile strength of like diameter fasteners. For example, in the fastening of wheels on heavy trucks, virtually all studs are threaded full length. While these fasteners have substantial shear strength, their function is to provide clamping force which in turn supports the load of the vehicle. If the clamp load is lost (loose nuts) and joint loading becomes shear, the studs will fracture and the wheel(s) will come off.
Typically, a joint utilizing torque or axial force on the fasteners is attempting to engage the geometry or friction of the mating surfaces to support the load. Think of the male fastener as a rubber band. The further it is stretched without breaking, the more clamp load it provides. This is why torque angle rather than torque loading (pound-feet) is the preferred method of maximizing clamp force. Angle, or linear distance up the thread helix, is a more accurate method of getting the desired stretch. Blind rivets also take advantage of a target clamping force by virtue of the load required to fracture the pin during setting. Shear strength of such fasteners is typically of secondary importance.
Terry
RV9A
N323TP

This is Tom,

Thanks for your input.

You are correct about the geometry issues that may apply. I consider your example to illustrate a combination load. The question was of simple shear.

Anytime a shear fastener is not secure enough to withstand the intended forces it will experience a combination of both shear and tension forces as the fastened structure experiences any displacement. This is why Truck and Automotive Wheel studs are large enough and many is to have a redundancy for safety sake, at the expense of weight, which for them is not a serious issue.

[terrykohler]

You are correct about the geometry issues that may apply. I consider your example to illustrate a combination load. The question was of simple shear.

Anytime a shear fastener is not secure enough to withstand the intended forces it will experience a combination of both shear and tension forces as the fastened structure experiences any displacement. This is why Truck and Automotive Wheel studs are large enough and many is to have a redundancy for safety sake, at the expense of weight, which for them is not a serious issue.
_
Tom:
Sorry I called you Bob. My example does not illustrate a combination load. Wheel fastening (and many other threaded joints as well) is all about clamp load. There is no redundancy designed into wheel fasteners for shear. If the fasteners (nut and stud working in combination) provide insufficient clamp force, the studs will fail. That's why in many threaded fastener applications, there is no mention of shear strength, only proof load. As to the original question, I was unable to decipher that the loading requirement was only shear.
Terry

[GAHco]

Originally Posted by tonyjohnson

Does anyone know the tensil and shear strengths of the following"

cs4-4 pop rivets

#4 stainless steel machine screws


I googled and checked all my reference materials but did not find that information.

Thanks in advance.

Tony

and

Tom:
Sorry I called you Bob. My example does not illustrate a combination load. Wheel fastening (and many other threaded joints as well) is all about clamp load.

Terry I chose to address only the shear issue because that is what I had the most and clearest knowledge on.

I still do not know the strengths of the Rivets, I just know that they are designed as shear fastener even though they are also capable of a tension load.

Your input has added an appreciated aspect of fastening dynamics such as friction during clamping and in many cases a very real consideration.

[tonyjohnson]

So, can anyone recommend a fastener that is suitable for my purpose as a "chicken fastener" for the canopy?

I have 1/8 holes drilled in the canopy frame and the canopy on five places on each side. My plan is to use #4 machine screws, stainless, in those places.

[cytoxin]

my money would be that the hollow aluminum rivet isnt anywhere near as strong as the ss screw. http://www.jeffsrv-7a.com/FUSELAGE/05-03-06.htm installed his canopy with aluminum screws.IIRC.

[terrykohler]

Tony:
Whether you are using machine screws or sheet metal screws (I think someone else recommended these, I'd suggest not), I'd be very concerned if the thread makes any contact at all with the plexi. Typically the plexi is drilled to size and then clecoed in place. The final size, whether for a fastener using a nut or one that threads into tapped aluminum structure, needs to be enlarged before final assembly - Any thread contact with the plexi will almost certainly lead to cracking.

Sounds like you want to fasten after you have bonded the plexi to the frame. Has the plexi been pre-drilled before assembly, or do you intend to drill after bonding? Pre-drilled, then use the machine screws in properly sized holes. If it's the latter, I would suggest that you consider using blind rivets. When the mandrel is pulled on a blind rivet, the shank will expand only up to the metal sheet you are attempting to join into. The portion thru the plexi should not expand and has no sharp edges to start fractures in the plastic. Hope that answers your question. Either approach will give you the "belt and suspenders" you are looking for.
Terry
RV9A
N323TP