OP
That's actually closer to reality than not.Save them for the next grade 2 fastener you use
Knowledge does not equal understanding, yet again
- Thread starter mrblaine
- Start date
Please explain how a bolt in double shear (or single shear for that matter) resists a greater force when more torque is applied to the nut.
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TJ2
TJ Expert
The magnitude of the shear yield stress in pure shear is (√3) times lower than the tensile yield stress in the case of simple tension.
TJ2
TJ Expert
OP
I don't know if I can explain it any simpler than that. There are basically two different types of forces that can act on a bolt:
1. Shear is a force that tries to cut a bolt across the shaft. Think cutting a wire with a wire cutter.
2. Tension is a force that tries to pull the bolt apart lengthwise. Think taking that same wire grabbing it a both ends and pulling in opposite directions.
The more you torque a bolt the greater its clamping force which is great if the goal is one of two things:
1. To bring two (or more) surfaces into as complete a contact as possible. For instance a wheel to a hub or a head to a block with a planed mating surface and a gasket.
2. In a type of bolted connection known as a Friction connection where the friction between the two surfaces resist the load, however friction connections are seldom used in steel design anymore because the value of friction connections are always less then the value of the bolt in simple shear.
Which brings me back to the subject of shear connections:
A simple shear connection is a bolt (or a pin... More on that later.) going through two pieces of material pulling (or pushing) in opposite directions. All force is applied to only one plane across the bolt shaft.
A double shear connection is where you have 3 pieces of material two applying force in one direction and one applying force in the opposite direction. This divides the force applied to the bolt shaft into two equal shear planes that are half the force applied. This is why a bolt in double shear is twice as strong as a bolt in single shear. A shock bolt is in double shear for instance.
Which brings me back to shear and the need for torque in a shear connection. In structural steel applications a vast majority of simple framed bolted connections are designed for shear using high-strength A325 or A490 bolts. Most of those are designated as shear connections solely dependent on the strength of the shaft to resist the shearing force of two pieces of steel. (There are connections where the threads of the bolt are included in the shear plane and those of a higher capacity where the threads of the bolt are excluded from the shear plane, but that is another conversation.)
All of those bolts are indeed torqued using visual indicators so that all plies of steel are brought firmly in contact with each other and to prevent the bolt from backing off. So the bolt is indeed pre-tensioned, however that is not done to increase the shear value of the bolt. There are many applications using shear connections where bolts are specifically not torqued and are simply hand tightened and the nuts are "killed" using either a weld stinger or a cold chisel. These connections have the same value as the torqued connections. I could also use pinned shear connections as an example. There are many extremely heavily loaded connections in structures such as bridges, conveyors and cranes that have no bolts in them only shear pins with only a washer and a cotter pin to hold them in place and zero torque applied to the shaft.
Sorry for the long post, I just finished my first cup of coffee.
OP
Those are not slip critical connections. We use bolts in vehicles and fabrication almost solely in slip critical connections where if the shank of the bolt ever sees shear forces, it is considered a failed connection.I don't know if I can explain it any simpler than that. There are basically two different types of forces that can act on a bolt:
1. Shear is a force that tries to cut a bolt across the shaft. Think cutting a wire with a wire cutter.
2. Tension is a force that tries to pull the bolt apart lengthwise. Think taking that same wire grabbing it a both ends and pulling in opposite directions.
The more you torque a bolt the greater its clamping force which is great if the goal is one of two things:
1. To bring two (or more) surfaces into as complete a contact as possible. For instance a wheel to a hub or a head to a block with a planed mating surface and a gasket.
2. In a type of bolted connection known as a Friction connection where the friction between the two surfaces resist the load, however friction connections are seldom used in steel design anymore because the value of friction connections are always less then the value of the bolt in simple shear.
Which brings me back to the subject of shear connections:
A simple shear connection is a bolt (or a pin... More on that later.) going through two pieces of material pulling (or pushing) in opposite directions. All force is applied to only one plane across the bolt shaft.
A double shear connection is where you have 3 pieces of material two applying force in one direction and one applying force in the opposite direction. This divides the force applied to the bolt shaft into two equal shear planes that are half the force applied. This is why a bolt in double shear is twice as strong as a bolt in single shear. A shock bolt is in double shear for instance.
Which brings me back to shear and the need for torque in a shear connection. In structural steel applications a vast majority of simple framed bolted connections are designed for shear using high-strength A325 or A490 bolts. Most of those are designated as shear connections solely dependent on the strength of the shaft to resist the shearing force of two pieces of steel. (There are connections where the threads of the bolt are included in the shear plane and those of a higher capacity where the threads of the bolt are excluded from the shear plane, but that is another conversation.)
All of those bolts are indeed torqued using visual indicators so that all plies of steel are brought firmly in contact with each other and to prevent the bolt from backing off. So the bolt is indeed pre-tensioned, however that is not done to increase the shear value of the bolt. There are many applications using shear connections where bolts are specifically not torqued and are simply hand tightened and the nuts are "killed" using either a weld stinger or a cold chisel. These connections have the same value as the torqued connections. I could also use pinned shear connections as an example. There are many extremely heavily loaded connections in structures such as bridges, conveyors and cranes that have no bolts in them only shear pins with only a washer and a cotter pin to hold them in place and zero torque applied to the shaft.
Sorry for the long post, I just finished my first cup of coffee.
In fact, your entire post is yet another example of knowledge not equaling understanding. You have an admirable amount knowledge about connections used in structural building. You have completely overlooked the single key difference in why each type is used. Understanding failed.
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Tray Burge
TJ Addict
Brianj5600
TJ Expert
OP
You can quit being a dickhead and try to learn something just about any time now. I promise it won't fucking hurt a bit.
I did my job of explaining, and took time out of my day to do it. All you have done is say that "people don't understand" but have failed to explain your side of the debate. Your comment, "Understanding failed." is not a convincing debate point. I refer to my previous post as a very detailed explanation as to how bolts work in any type of connection. Shear vs Friction vs Tension. Please convince me and others differently with facts instead of rhetoric...
The basic premise of the first post in this thread is that, "People are dumb asses, because they don't understand how bolts work," but you haven't provided any proof.
By the way... A bolt will NEVER have a higher value in friction than it does in shear.
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OP
Alright, this deals with the most common connection we deal with. In context, this is an automotive related site, we discuss automotive related things along with fabrication of various items we use. The vast majority of bolted connections we use and the one that started this post is a slip critical that relies on the friction developed between the faying surfaces to lock the bolted members in place. In that type connection, the bolts sees very little of the load when it is torqued properly and at the point when the bolt does see the forces, we can consider the connection failed.
We do not use snug tight single or double shear connections for cyclical loading so how they work has no relevance.
This will help.
https://www.boltscience.com/pages/the-basics-of-bolted-joints.pdf
Brianj5600
TJ Expert
I don't know if you meant to be condescending from the beginning, but that is how I took it. I didn't just buy my first tool set.
When it comes to the coilover spacers, does this mean the friction between the spacer and the mount takes the force from the coilover? The bolt doesn’t take any shear stress?
We use air shocks on our race buggies in a similar fashion and I’d always thought the bolt takes the force. We use the air shocks as bump stops as well so it might be slightly different than a Jeep with separate bump stops.
I understand what is in that article. I explained all of that in my previous post...
So let's go back to your very first post in this thread... The sleeve in the picture that you show obviously takes all the clamping force of the torqued bolt. This would mean that in what you are referring to as your friction (slip-critical) connection that the ends of those cylinders become one of the faying surfaces in the connection. Is that correct? (I'm asking this question, because I only see the cylinder and not the entire connection.)
I just posted the same basic question and am curious to the answer as well. And for the same reasons that you are.
If I am envisioning the connection like I think I am, the bolt is in double shear whether Mrs. Blaine thinks it is or not and the shaft of the bolt is taking the load in bearing (Most likely with threads excluded from the shear planes for fatigue purposes.) therefore the torque of the bolt has very little to do with the capacity of the connection.
The bolt does not take any shear stress. If it did, there would be a constant knocking sound and the mount would eventually wallow out. Again, it's the same reason the track bars and all the control arms need to be fully torqued. We don't want those connections to slip. And you probably don't want your air shocks to slip either.
In the case of the first post, the spacers collapsed under the load of the bolt's clamping force and allowed the connection to slip.
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TJ2
TJ Expert