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Unread 06-09-2011, 05:28 AM   #31
Technohead
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Quote:
Originally Posted by mike_breaker_5 View Post
op's bumper will fail in a recovery. stop denying it, and for gods sake don't compare a solid mounted clevis mount to a piece of sheet welded to another piece of sheet, the welds will fail plain and simple. lets stop all the debate and go yank on the darn bumper for gods sake. holy crap people it's a poor design and needs re-worked!
What are you talking about solid mounted clevis? The clevis mounting tabs on my Hanson bumper are welded around the perimeter very similar to the OP's. And mine have considerably less weld material. Like I said, assuming the welds have reasonable penetration then there is no problem.

Here's some simple math. With weld penetration of 3/16" two 4" long weld beads (estimated length on OP's bumper) are good for 50k pounds or so in tensile load.

And 5/16" is sheet metal? The only sheet metal in the equation is the sheet metal to which this bumper is mounted.

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Unread 06-09-2011, 05:58 PM   #32
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Standard mild steel mig wire has a yield strength around 70ksi when welded perfectly. I've seen what happens when a 3/4" thick bead breaks (took a 25ton crane mind you, broke the weld, fight poul out of the base material). The average good stuck can put well over 15k of force on a single point...

bead cross section, not length, is what determines ultimate strength. A 3/16" bead is good for about 13-15k. Assuming no inclusions and penetration of half the thickness of the thinnest material you've welded together. I can't even guess as to the strength of those chicken turds.
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Unread 06-09-2011, 05:59 PM   #33
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Quote:
Originally Posted by Technohead View Post
What are you talking about solid mounted clevis? The clevis mounting tabs on my Hanson bumper are welded around the perimeter very similar to the OP's. And mine have considerably less weld material. Like I said, assuming the welds have reasonable penetration then there is no problem.
The welds aren't the issue here with the OP's recovery shackles. It's teh strength of the shackles themselves and the fact that they do not anchor far enough back through the bumper supports. His welds may indeed stay put on the 5/16" plate, but the steel shackle mounts he used may peel away from the weld bead because they are not mounted properly and look too thin to be used for serious recovery. As I described before, they look like door knockers, not shackles.

Quote:
Originally Posted by Technohead View Post
Here's some simple math. With weld penetration of 3/16" two 4" long weld beads (estimated length on OP's bumper) are good for 50k pounds or so in tensile load.
Again, the weld bead may not come loose, but the thin metal his shackles are made of may pull away from the welds.

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Originally Posted by Technohead View Post
And 5/16" is sheet metal? The only sheet metal in the equation is the sheet metal to which this bumper is mounted.
I certainly was not saying 5/16" is sheet metal. I was saying that the shackle mounts do not know whether they are welded to 1/8" sheet or 1" plate. If not anchored properly they can and will peel off the face of any metal they are welded too, regardless of weld bead penetration. Even if welded properly with good penetration and good weld bead strength, the weak point now becomes the metal the shackles are made of themselves. That small square area of steel that makes up his "mounts" is weaker than the weld bead and will shear off.
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Unread 06-09-2011, 07:06 PM   #34
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The bumper looks good. I am not sure about the whole recovery point argument but better safe than sorry always on those. The bumper does look really good though.
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Unread 06-10-2011, 04:04 AM   #35
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Quote:
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Standard mild steel mig wire has a yield strength around 70ksi when welded perfectly. I've seen what happens when a 3/4" thick bead breaks (took a 25ton crane mind you, broke the weld, fight poul out of the base material). The average good stuck can put well over 15k of force on a single point...

bead cross section, not length, is what determines ultimate strength. A 3/16" bead is good for about 13-15k. Assuming no inclusions and penetration of half the thickness of the thinnest material you've welded together. I can't even guess as to the strength of those chicken turds.
The weld wire probably has a yield as high as 70ksi but the flat iron certainly does not. More like 35ksi.

Of course length matters. How do you think the cross section is calculated? LENGTH * bead width. It does not make any sense to say a 3/16" bead is good for 13-15k without saying how long the bead is.

Where do you get this number of 15k for the "average good stuck"? I have never stalled out my 9k winch and never had to use double line but have used it to pull myself out from some nasty spots.
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Unread 06-10-2011, 06:20 AM   #36
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cross section is always measured perpendicular to the long dimension of a solid. Always. Sort of the definition of the word. Bead length has no bearing on the strength of the weld it's self. You aren't wrapping your head around what the forces are doing and what factors can increase the stress concentrations in a weld or even a machined step similar to that.

As for the "good stuck" numbers, a winch pulls in a different manner than a vehicle tugging another out, impulse loading in those cases often bends 10-15k rated recovery points (as seen with my own eyes) and can go so far as to snap 30k rated straps that were in good operable condition. Impulse loads are a mean b***.

Oh, if that bumper was actually iron those shackles would have fallen off on their own right after the rest of it fell apart at the welds.
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Unread 06-10-2011, 07:50 AM   #37
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Unread 06-10-2011, 08:39 AM   #38
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if your highcentered your estimated "just to move" with steady force is around 2.5x the vehicles weight , not snatching is roughly 12,000 lbs(technically thats just a minimum),
would you hang 3 zjs from one of those brackets off a cliff???
using a snatch strap could easily double or triple that amount of force on to 1 recovery point
elasticity and momentum are a scary thing


edit, found the page i was looking for https://www.juststraps.com.au/pdf/4x...covery2007.pdf
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Unread 06-10-2011, 01:14 PM   #39
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. . . Bead length has no bearing on the strength of the weld it's self. . .
Of course it does. You are talking about stength per unit length. A weld 2" long can resist twice as much force as a 1" long weld can resist. Think about the limiting case: A weld with 3/16" bead width that is only a small fraction of an inch long (like a tack). I could break that with my hands.
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Unread 06-10-2011, 02:45 PM   #40
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The factory tow hooks and brackets have about eight big bolts holding them on. I added junk yard tow hooks to my Jeep so I know what PIA it is to get them off. I would suspect that set up is a lot stronger than any recovery point welded to a metal plate could ever hope to be. I have no idea about the physics behind the strength of a weld but I would probably not trust the setup in this thread just based on how it compares to a factory tow hook.
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Unread 06-10-2011, 05:29 PM   #41
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. . . I have no idea about the physics behind the strength of a weld but I would probably not trust the setup in this thread just based on how it compares to a factory tow hook.
Then you should crawl underneath your Jeep and take a look at the welds holding all the different brackets to the unibody. And how thin the unibody structure is. Then compare to this bumper. If anything, the bumper is complete overkill.
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Unread 06-10-2011, 05:48 PM   #42
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try Pulling a full 3/16x3/16x3/16" tack like that off bare handed, heck, use a 5lb slide hammer. Bet you can't do it. you'd bend the metal first if you tried to side load a "tack" made as you describe.

The length will help resist bending, it does nothing for a straight on load applied to that mount.

i do make a decent portion of my paycheck from sticking two pieces of metal together and having them last more than one use.
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Unread 06-10-2011, 05:48 PM   #43
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try Pulling a full 3/16x3/16x3/16" tack like that off bare handed, heck, use a 5lb slide hammer. Bet you can't do it. you'd bend the metal first if you tried to side load a "tack" made as you describe.

The length will help resist bending, it does nothing for a straight on load applied to that mount.

i do make a decent portion of my paycheck from sticking two pieces of metal together and having them last more than one use.
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Unread 06-10-2011, 06:19 PM   #44
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. . . The length will help resist bending, it does nothing for a straight on load applied to that mount. . .
Yes it does matter. If you can't grasp this very basic fact then no point discussing further.
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Unread 06-10-2011, 08:36 PM   #45
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Yep, I'll stick to my welding and engineering education. thanks for the lively discussion.
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