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OT engineering fastener load calculation stuff

wheelieking71

wheelieking71

Diamond
Joined
Jan 2, 2013
Location
Gilbert, AZ
Okay, my google-fu skills have run dry.
I am looking for load specs for 3/8-16 U-nuts. Something like this: Amazon.com: The Hillman Group 58456 3/8-16-Inch Regular Extruded U-Nut, 15-Pack: Home Improvement
Basically trying to figure out how many pounds that thing can cold in a straight line pull before failure. It has a grade-5 bolt in it.
I know the spec for 3/8-16 bolt is roughly 6500psi. But what does that equate to in a straight line pull in lbs?
I am assuming the 3/8 grade-5 bolt would be significantly stronger than the U-nut?
 
100,000psi yield.

~5/16" root diameter = .0769sq in

Move some decimals and you get 7690lbf.

Go to 3/8-24 and you'll get an extra 1000lbf.

Sent via CNC 88HS
 
Cole2534 said:
100,000psi yield.

~5/16" root diameter = .0769sq in

Move some decimals and you get 7690lbf.

Sent via CNC 88HS
Click to expand...

Load Calculator | Fastenal

According to that, the shear strength would be 4880. And I know bolts are stronger in shear than tension. So, I am not following your math.
I'm not looking for lbf. Just lbs. How much actual weight in lbs can a grade5 bolt pick up in a tension arrangement.
Is that what the fastenal machine is calling yeild strength? (kinda close to your number)
 
wheelieking71 said:
Load Calculator | Fastenal

According to that, the shear strength would be 4880. And I know bolts are stronger in shear than tension. So, I am not following your math.
I'm not looking for lbf. Just lbs. How much actual weight in lbs can a grade5 bolt pick up in a tension arrangement.
Is that what the fastenal machine is calling yeild strength? (kinda close to your number)
Click to expand...

No, they're not. Tension is ideal loading.

Sheer is a special case of tension qnd generally considered ~2/3 of ultimate, 4880/.666 = ~7300lbf.

The shear plane is 45° from the normal axis, and being a 45 this means the sides are equal (.707) and the hypotenuse is 1.

Sent via CNC 88HS
 
Cole2534 said:
No, they're not. Tension is ideal loading.

Sheer is often ~2/3 of ultimate, 4880/.666 = ~7300lbf.

Sent via CNC 88HS
Click to expand...

Interesting. So, take the china-mart bolt factor in to account, and I am probably looking at about 6,000lbs?
But, what about the U-nut? I can't find shit for specs on those things.

Also, what do you think would be a good safety factor when choosing hardware for a winch bumper? I am thinking at least 2?
 
Unsure on the nut, but I wouldn't be surprised if it held every bit as much as the screw. However, I feel the ultimate limitation will be what the nut clips onto.

Sent via CNC 88HS
 
wheelieking71 said:
The material is plenty strong.
Click to expand...
Then why the spring nut and not direct thread?

Not to be intentionally condescending, but are you up to the task of designing this item? The only 2 items you've known in this thread were wrong, you don't understand the difference between ultimate and tensile and the base material is 'strong enough' to require stress analysis of gr5 screws yet requires a spring nut.

Sent via CNC 88HS
 
Cole2534 said:
Then why the spring nut and not direct thread?

Not to be intentionally condescending, but are you up to the task of designing this item? The only 2 items you've known in this thread were wrong, you don't understand the difference between ultimate and tensile and the base material is 'strong enough' to require stress analysis of gr5 screws yet requires a spring nut.

Sent via CNC 88HS
Click to expand...

No, I am not up to the task. That is why I am asking. I did not design it. I bought it. The 3/8-16 bolts and U-nuts were supplied (china mart bolts).
The base material is 10ga. Although, the mounting holes in the base material are big enough for 1/2" hardware and slotted.
So I am sure that needs to be taken in to consideration (the U-nuts pulling through the holes).

I just can't believe this is the supplied hardware for a winch-bumper. Lets say: 12k winch with a snatch-block and a safety factor of 2 = 48,000lbs.
This is not the hardware I would want to trust in that situation. And, I didn't. I used 1/2" grade-8 stuff (no U-nuts either!).

Just trying to figure out how they landed on this cheap shit to mount what is supposed to be a high-end winch bumper.
 
Ah! Now I see. A winch mounted in a bumper is much more complicated than simple shear of tension on a bolt. Their design may have been perfectly sufficient.

Sent via CNC 88HS
 
I am not a doctor, I mean, engineer, but reading through this I'd ask the next question, which is what is the load path from the winch, through bumper, and into the chassis of the car?

If this is a "typical" bumper, it's probably a low alloy steel, of perhaps 50Ksi yield. The sectional forming will give it greater stiffness than a flat sheet, but not enormously greater strength, so you have to worry about it deforming under load.

If the load path into the chassis is through deformable "horns" that are then anchored to the chassis, the bumper will behave a little like a bow being drawn to shoot. I'd be concerned about how the bending stress through the bumper would deform the mount horns too.

If there's any way to run some ~2" x 1/4" cold rolled struts directly from under the winch/bumper attachment points to the actual chassis and find some good anchors there (bolt through one of the many slots or holes usually present), I'd feel a lot better about using more of the nominal 24 tons of draw force available.

[The above may be pointless twaddle, in "winch" case dismiss]
 
Cole2534 said:
Ah! Now I see. A winch mounted in a bumper is much more complicated than simple shear of tension on a bolt. Their design may have been perfectly sufficient.

Sent via CNC 88HS
Click to expand...

Well, me not being an engineer, if I were to design, build and sell a WINCH bumper that mounts to the stock bumper mounts?
I damn sure would not use significantly smaller/weaker hardware to mount it than the factory used to mount the original equipment non-winch bumper.
Whether an engineering hand-book and some math says it is adequate or not.

I don't trust those damn U-nuts. I just went out and scrutinized one. Best I can count there are 4.5 threads in it. That doesn't even meet the std 1X diameter thread depth rule.
And, they are slid over a hole that is not that much smaller then they are wide (like I mentioned, I used 1/2" hardware with no drilling).
 
Keep in mind that the charts are best case, and in all engineering there is a safety factor...I life threatening it is 6/1 or more, steam boilers are 6/1. And with multi bolts there is the zipper factor where one fails and overloads the remanding bolts. THIS is why engineers get the big bucks... not for the lay man to do...Phil
 
wheelieking71 said:
Interesting. So, take the china-mart bolt factor in to account, and I am probably looking at about 6,000lbs?
But, what about the U-nut? I can't find shit for specs on those things.

Also, what do you think would be a good safety factor when choosing hardware for a winch bumper? I am thinking at least 2?
Click to expand...

I would look at eye bolt ratings.
 
digger doug said:
I would look at eye bolt ratings.
Click to expand...

I did. They are lower, much much lower than the numbers I (and Cole) are coming up with for a grade-5 bolt.
I don't know if that is because they are forged? Designed for side-loads? Cut threads rather than rolled? Specs specifically for lifting?
But I don't think that is a good reference.

Which brings me to this:


Cole2534 said:
On a hoist, yes, 4:1 minimum. On a winch I'd be content with 2:1.

Sent via CNC 88HS
Click to expand...

WHY? I actually think a winch pull could be significantly more dangerous than a lift.
If a lift fails? The load is coming down. Straight down if it is a single line lift. As long as your not under it, you should be good.
If a winch decides to separate from a vehicle? You would like to think its going to go in the direction of the pull. But, no guarantees on that.
 
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