Great work taking the time to design something before you start. and good work colour coding things and then describing them - it makes it very easy to discuss.
There's a few design themes going on here I need to discuss.
Less parts are better than more (also if it's not structural it's cosmetic- I'll get to that)
Plate isn't strong on it's long side, it's strong on edge (and corners are your friend)
Design to put welds into the lowest stress possible.
Only use thick material when there no other option, because otherwise it's just adding weight and fabrication complexity for no reason (i.e 7 and 10mm plate is a pain to work with and weld)
I'll discuss each theme separately. I'll out the RUF aside for now, that's a whole different can of worms.
Less parts are better than more:
Have a look at your parts and see which ones are doing very little (or nothing at all)
The red "non structural" parts should be
very structural. They should be providing the bar with most of its strength. In the case of an ARB bar, for example, those parts provide the bar with ALL of its strength, as the winch is mounted feet forwards. In an ARB bar they're typically only 3mm thick.
Have a look at the outside top mounts on your design. You have a 7mm thick green tab that's only picking up one bolt, it then is welded to a 7mm plate (is that even a stocked thickness of flat bar?) what does that weld look like? it's not very long (50mm?) it will need to be prepped as a FSBW. Then you've welded the red bit on top. Why not make that all one piece up the side? why not make that outside plate pick up both bolts like the inside plate?
The crossmember your winch plate sits on is very thick but isn't very strong because it's lying across the direction it's loaded. Remember the winch is trying to peel it up at the back and forward. Imagine the winch drum stopped and the car started to turn around it - that's the direction the force is in.
There is no reason to put a second plate on top of the crossmember, it's not doing anything except providing the right size footprint for the winch. At that point you have 17mm of steel and its adding almost no strength to the bar. With a couple of small changes you could make that whole top crossmember/winch plate out of 3mm and it would be strong enough. I'll explain that in a minute.
I'm not sure what the big green blocks are under the winch but they're not really adding anything because they're on the wrong side of the crossmember to help. You also have a stock recovery point and steering damper mount in that area.
The crossmember under the factory tube isn't doing enough to bother with, again, because it's only connected at the ends and in one plane. If you clamped one end of that plate in a vice you could twist it easily with a big shifter on the other end because it has no corners - it's weight without strength.
Whilst you've picked up both sides of the chassis, the outside plates are only picking up one bolt and there's a lot of material between the inside and outside green plates that isn't doing anything and isn't adding any strength to the bar.
So there's parts that aren't doing anything, and lots of heavy steel what can't do enough because of the plane it's in.
Plate isn't strong on it's long side, it's strong on edge (and corners are your friend)
Each part you've designed is in isolation. You've chosen plate thicknesses that reflect that each part can't work with other parts to increase its strength.
I assume you intend to weld the 10mm winch plate to the front plate with the cutout for the hawse in it. That's the key. If you think about making everything into a box you can turn thin material into very strong material without weight. Make the crossmember the winch plate is welded to meet the front plate and weld them together. because that front plate has two bends in it and is then fully welded to the crossmember/winch plate, it's now VERY strong.
Now, copy that at the back - put a strip of plate across the back of the winch plate/crossmember and it won't be able to bend up. Note that's what Beery did here:
Quote:
(The red outline represents a plate that will be added to stiffen the winch plate)
Most of that crossmember/winch plate just doesn't need to be there, and/or doesn't need to be very thick at all. 5mm would be overkill, 3mm is fine, but at the mounting holes for the winch it would be ideal to be thicker to prevent the bolts pulling through or bending the base plate (this is a problem with going feet down that ARB doesn't have with mounting the winch feet forward) so, add some weld washers or a doubling plate on the underside just where you need it. I keep the circles from the inside of my holesaw cuts to use as weld washers for this reason - now your 3mm of plate is 6mm where you need it, 3mm where you don't.
As has been pointed out, there's no strength where the outrigger connect. They will fold up and into the bodywork with just a very light nudge. Making that whole side plate one piece and then tying it into the back of the crossmember/winch plate would help, but really, the tube needs more support further along it's length.
Design to put welds into the lowest stress possible.
Your design puts almost all the winch load onto two welds about 75mm in length. I know there are other welds, but for a few reasons they can't help much. The outside plates are only held to the chassis on one bolt, so they can just twist. also, there's no bracing on the crossmember between the inside and outside plates, so that will bend readily. The result is that the weld on in side green plate to the crossmember is very highly loaded and the winch is trying to tear it open - it's pulling on it, which is when welds are weak. It's also a single sided fillet weld, because your design puts the RUF bracket on the inside of it, there's no room for another weld in there.
I can see some straps between the upper and lower crossmember (also in green) but they aren't doing very much because the lower plate isn't braced or gusseted. The bottom plate will bend readily.
As it sits, the winch plate is fillet welded down to the crossmember. Maybe (?) two of the winch mount holes will go through both plates. It seems like a lot of fillet welding and steel that isn't doing anything.
Only use thick material when there no other option, because otherwise it's just adding weight and fabrication complexity for no reason (i.e 7 and 10mm plate is a pain to work with and weld)
I've spent a lot of time talking about thicknesses of your material, so that's well covered, but here's something else - that front plate sees a lot of work. not only does it get bumped into things and will likely have stuff mounted on it, it also has the hawse bolted to it. The hawse takes quite a lot of load when you're winching on a big angle and that single piece of plate will move around. - again, a strip over the top, even 25mm wide, following the whole front plate will add a LOT of strength and support. 3mm is fine, 2mm is too weak.
How I'd move forward:
Redraw what you have but wither everything at 3mm. Make the winch plate and the top crossmember one piece. double up the winch plate area underneath with some 50X3mm flat bar running fore-aft to keep the winch sitting flat when loaded up.
Weld the winch plate/crossmember to the front plate right across the car. Remove the speed holes in the front plate on the angled sections - that area needs to be strong.
Make the outside side plates all one piece right up the side and make them pick up both bolts and run the full depth of the top crossmember. With a brace across the back of the crossmember/winch plate, that would be quite strong.
However, that still puts excessive load on the welds in my opinion, and that's largely because you've designed the bar to it so far in the front of the car. Putting the winch back as far as possible is cool, but there's no reason to put the whole bar so close to the end of the chassis - it just makes it hard to design. if you pulled it forward a little, the uprights could go in front of the winch plate which would take the load off the welds.
Oh, an aside - this design has no provision for recovery points and restricts access to the crossmember to use a sling, and that's only due to the cosmetic filler below the winch plate.
I don't have the time to draw it up in CAD now, but here's some hand sketches of what I mean.
Of course, the whole issue with this though is it still only mounts off the end of the chassis with the four factory bolts. As discussed, that's not really strong enough. It's OK for a bar only, but I wouldn't winch off it.
soooo, that entire plate needed to be re-done with the bends further inwards. If I had of just mocked it up out of MDF/corflute I could've picked up on it.