Blind pop rivet tensile strength

[asid61]

McMaster rates pop rivets in tensile strength as well as shear strength. A 3/16" aluminum blind pop rivet has a shear strength of 310lbs and a tensile strength of 500lbs.

McMaster-Carr

If the rivet is holding two plates together, am I right in assuming that shear strength is the force on the blates going in opposite directions perpendicular to the rivet, and the tensile strength is the force required to pull the plates apart parallel to the rivet? Everything I’ve read about rivets says that they shouldn’t be used in tensile applications, so why is the tensile strength so high?

[Joe_G]

Your interpretation of the loading is correct.

The numbers given are static load ratings, meaning that “if I hang 500 lbs from this rivet, it will exceed its rating and fail.” However, FRC loads are nearly always dynamic or cyclical in nature to some degree. This means that they repeat themselves. It is my understanding that this kind of cyclic loading is likely to work a rivet loose over time when applied in tension, since it will pull on the deformed flange and loosen it some. It’ll take a lot of force to fail a rivet in tension outright, but it can easily loosen to the point of not being very useful, as your pieces will no longer be firmly held together.

[OccamzRazor]

The tensile strength is often related to the “pull out strength” of the rivet. Rivets will almost always fail in shear first but there are cases where the rivet being used is tougher than the plate and the plate will crush or tear(thick steel rivet and thin aluminum plate for example). It usually requires more strength to pull a rivet out than to shear it which is what the datasheet is letting you know. The reason you do not use a rivet for a tensile example is because you rarely use one rivet in an application so adding multiple rivets makes the force to shear in that joint increase whereas the pullout force for that ONE rivet still remains about the same no matter how many you add because you are only relying on the head of the rivet and the friction in the expanded joint to hold it in. If separation occurs then shear will most likely happen and cause failure.

Joe is spot on about dynamic and cyclical loads where vibration or fully reversed loading occurs. These types of loading conditions in the real world are treated with a high factor of safety (6 to 12 times) over static loads and more often than not are exactly what you experience on a robot during competition.

Our robot chassis this year was all riveted construction with only two joint welds. http://www.yetirobotics.org/wp/our-robot/

We sheared the riveted angle plate that stops our gravity claw twice during competition so we added more rivets to fix it at worlds since it was a 2 minute fix. Once one rivet shears it usually unzips and breaks the rest of them soon after as the kids got to see.

Hope that helps!

[GreyingJay]

With respect to rivet material, I was reading somewhere that said you should choose the same material of rivet as the material you are fastening, e.g. aluminum rivets for aluminum plates.

I can understand wanting thermal expansion properties to be the same for construction of long-term, permanent structures like vehicles. But does this apply for FRC robot construction? In other words - why wouldn’t I always use, say, steel rivets, for strength?

[asid61]

With respect to rivet material, I was reading somewhere that said you should choose the same material of rivet as the material you are fastening, e.g. aluminum rivets for aluminum plates.

I can understand wanting thermal expansion properties to be the same for construction of long-term, permanent structures like vehicles. But does this apply for FRC robot construction? In other words - why wouldn’t I always use, say, steel rivets, for strength?

I would argue that aluminum rivets will work just as well as steel ones for most applications in FRC. We avoid steel rivets because it is difficult to drill them out. Any time we would have to use steel, we just switch to a screw.

[Mike_Marandola]

With respect to rivet material, I was reading somewhere that said you should choose the same material of rivet as the material you are fastening, e.g. aluminum rivets for aluminum plates.

I can understand wanting thermal expansion properties to be the same for construction of long-term, permanent structures like vehicles. But does this apply for FRC robot construction? In other words - why wouldn’t I always use, say, steel rivets, for strength?

Not really in FRC, but it humid environments it is best to use similar metals to prevent galvanic corrosion.

Source

[philso]

With respect to rivet material, I was reading somewhere that said you should choose the same material of rivet as the material you are fastening, e.g. aluminum rivets for aluminum plates.

I can understand wanting thermal expansion properties to be the same for construction of long-term, permanent structures like vehicles. But does this apply for FRC robot construction? In other words - why wouldn’t I always use, say, steel rivets, for strength?

We ended up using some 3/16" steel rivets in this years robot. The aluminum ones held up just as well and were lighter. We probably had to cut some extra “speed holes” due to the steel rivets we used.

[Wrysgen]

Hello, I have a challenge, which is beyond my abilities and have joined the forum hoping to get some informed opinion and figures concerning shear strength relating to riveted components.

I hope you don’t feel this is too cheeky.

OK here’s the story. I own an Aston Martin Vanquish S. The frontal nose cone is a composite around 5mm thick. Below this is located a splitter the full width of the nose cone, this is formed from a glass fibre material and is around 2mm thick max and is profiled to give it some added strength.

The splitter is held onto the underside of the nose cone using VHB tape running the full width of the splitter and 13 rivets along the back edge of the splitter which secures it to the underside of the nose cone.

Now when I bought the car, the splitter was missing. I understand that the car had had a frontal impact which had damaged the nose cone and presumably smashed the splitter. The original rivet holes were deformed due to this impact.

Aston Martin fitted a new splitter for me at great expense and after driving the car for roughly 20 miles I found that the splitter had disappeared. The car did not suffer any impact, but would have been under some load in terms of airflow and heat.

Aston Martin claim that I must have hit something, despite the fact that there was no damage to the car of any kind. I claim that the new rivets holding the splitter should not have been refitted to the original deformed holes. Aston Martin state that the splitter can come off if sustaining an impact of 1 MPH. This seems incredible.

So here’s why I’m requesting some engineering calculation.

Is it possible to calculate the force required and therefore the speed, based on the information provided above and a vehicle weight of 4,100lb to:

A. Shear the rivets and VHB tape in a horizontal direction, resulting in the splitter dropping off the car. This would indicate the speed required to achieve this outcome
B. Rip out the rivets and shear the VHB, assuming a 25% reduction in effective rivet holding strength due to deformed rivet holes. This would also indicate the speed required to achieve this outcome

If any helpful engineer is interested in calculating some numbers and wishes to communicate, my own email address would be best, I can then also email a picture of the nose cone and splitter which might help clarify the make up and location of the parts Email - [email protected]

Thank you and regards
David