laminated cross member( so to speak )

[Mr.OverKill]

ok, here is the idea in a nut shell, slick belly with extra strength above 3/8 plate with out the need for ribs or extra gussits. all you need is the trany bolts and mount bolts counter sunk on the cross member.

the theory is take 3 1/8" ( or more thinner ) sheets of sheet metal all cut to the size and shape you need and have the center sheet remane whole ( un drilled ) and then take one of the two other plates and drill a serries of 3/8" holes in lines every 3" for a total coverage of 2/3 ( 1/3 to the right of the trany and 1/3 to the left ) of the plate then alternate the same patturn on the other plate, when this is compleated meta the 3 plates together being carefull to make sure that the holes drilled in the top plate do not line up with the ones on the bottom.

the next step is to begin plug welding the plates togetherstarting in the furthest in board holes top then buttom alternating top and bottom and in a spiral star patturn ( like torqueing an intake ) to prevent warpage, finaly you weld around the outer seams, then grind flush all welds creating the appearance of a solid plate that turns out stronger than something twice as thick and solid, same concept as either plywood or my favorate, armor plating!

finally drill and bolt the belly pan inplace with the tranny and trans case, that is when i will be welding the LA attach points in place for my rig.

thoughts, comments, counter points and suggestions are all being solicited on this point of topic:lecture:

 

[Mr.OverKill]

ok, here is the idea in a nut shell, slick belly with extra strength above 3/8 plate with out the need for ribs or extra gussits........

thoughts, comments, counter points and suggestions are all being solicited on this point of topic:lecture:

i truly cant believe you all are speechles, not one comment, suggestion or counter point, ont even a " hmmm thats interesting" or " it will never work":wow:

 

[Goatman]

It will never work......


The concept of a sandwich structure to add strength might be a very good one. I'm unclear exactly where the crossmember would go. Are you talking about a full belly pan, or replacing the stock crossmember?

 

[5-90]

Gimme a chance - I just saw this...

If it weren't for the fact that you're welding thru the drilled holes in the centre plate, I'd have given it a thumbs down right away... Why? Drilling holes that aren't filled create stress risers - and drilling lightening holes in something is a great way to make a weak part.

However, why are you drilling out the centre plate? Are you trying for a composite - or a crossgrain effect? If you're going to do that, maybe something like wriggly tin, arranged so the wriggles go crosswise, would give you more strength (read: stiffness) than what you're thinking now - without having the stress risers around the holes (still an issue - even though you're welding them to the other plates, there's still the heat affected zone to worry about.)

I'd probably do something like this, but I'd do the crosswise wriggly tin sandwich, and I'd probable rivet it (since the rivets will fill the drilled holes, if you do the job right.) That way, you could paint everyting before assembly and be assured of full coverage.

You can smash down the wriggles to make it all thinner - but you'd have to have some way to hold it while you drill and rivet.

I'd like to hear more of what you're thinking, so I can see if we can't refine this idea some more. There is potential!

5-90

 

[RichP]

Have you ever looked at the belly plates that are on YJ's and TJ's. PIA things when it comes drain time on the tranny and TC but it sure does protect alot compared to the XJ crossmember. I've wondered if one could be adapted to fit an XJ, it already has the tranny spacer and such.

 

[Mr.OverKill]

ok,have the center sheet remane whole ( un drilled ) and then take one of the two other plates and drill a serries of 3/8" holes in lines every 3" for a total coverage of 2/3 ( 1/3 to the right of the trany and 1/3 to the left ) of the plate then alternate the same patturn on the other plate, when this is compleated mate the 3 plates together being carefull to make sure that the holes drilled in the top plate do not line up with the ones on the bottom keeping the un drilled plate in the center/ middle

the next step is to begin plug welding the plates together, starting in the furthest in board holes top then buttom alternating top and bottom and in a spiral star patturn ( like torqueing an intake ) to prevent warpage, filling all the holes compleatly, finaly you weld around the outer seams, then grind flush all welds creating the appearance of a solid plate that turns out stronger than something twice as thick and solid, same concept as either plywood or my favorate, armor plating!

finally drill and bolt the belly pan in place with the tranny and trans case,:lecture:

slightly revised wording, the idea is the alternating grane thing. this is for the cross member and a belly pan combination. the heat embrittlement can be countered by pre and post heating of the belly pan, well it is only a theory of mine, a lot of work for a little gain. we shal see.

 

[5-90]

So, will you have an oven large enough to heat treat the thing all at once, or are you going to do it with a torch? If you use a torch, you're practically guaranteed uneven heating and resulting internal stresses.

I still like the rivet idea - especially for prototyping at least. The lack of heat stresses should help, and the reduction in strength due to the drilled holes should be minimised by the hole being filled by the rivet as it collapses.

Yeah - the idea of leaving in some sort of access for various drains won't go amiss, either - a full belly pan can be a pain unless you really plan the thing (like I need another project - how in Ned am I going to get everything done as it is? :laugh3: )

Part of the issue is that the grain orientation in sheet metal is nominal at best - plywood gets is strength (as you probably know already) from alternating grain directions - either a direct alternation at 90*, or with specialty lays for light aircraft. The idea of "grain," as you're applying it, would refer to some sort of continuous - or nearly continuous - fibres throughout the piece giving some sort of reinforcement - which you won't get with mill metal.

Of course, there is always composites (perhaps a fibreglas sandwich plate, laid over and under with sheetmetal?) which would give you the lightweight fibre idea while retaining some of the protection of metal.

In fact, that had a lot to do with my "wriggly tin" idea - since there's isn't a true grain in metal, you can simulate one structurally, and wriggly tin is perfect. You can take that idea as far as you want - do only one layer for strength in one direction, or alternate layers (again, like plywood) for multidirectional reinforcement. By compressing the plates before they are attached, you can get a thinner panel and pick up some strength from prestressing the strength member (like bolt preload, or prestressed concrete.) The material wanting to "spring back" to it's normal profile will help to resist panel deformation.

5-90

 

[Mr.OverKill]

the holes are not drilled for drainage they are how you would the 3 layers together, exhample take sheet 1 drill a hole in it, take sheet 3 drill a hole in it then place sheet 1 and sheet 3 on opposite sides of sheet 2 and completely fill the holes up with weld secureing them all together. is that clearer


and the pre and post heating would be accomplished by heating pads ( industrial type ) i use on aircraft carriers when i am welding on the hull and structural componants that are hy100 rated, the rod i would use would be 11018 or dual shield for faster filling.

 

[MaXJohnson]

four reasons I can think of to laminate:

1.) as already mentioned, alternating grain structure; the plywood example

2.) appearance. Laminate a pretty skin over a structural, but ugly core; formica on your countertop.

3.) taking advantage of the properties of two dissimilar materials. Wood clad with fiberglass would be an example. Armor plating would be another.

4.) adding strength to lightweight material. A foam core clad in aluminum create a strong, but lightweight panel.

Steel doesn't have enough of a grain structure for #1 to be an advantage. Using steel layered with steel doesn't change the appearance or material properties of the panel, so that shoots down #2 & #3. Finally, steel clad with steel yields no benefit in weight savings.

The only advantage I can think of is to use up material you already have laying around or working with a thinner gage that is easier to fabricate with a limited set of tools.

Laminated panels are bonded together across 100% of the surface. This eliminates any slipping between panels to maximize the beaming strength of the panel. A solid panel of 3/16" steel would be stronger in this manner than three sheets of 1/16" spot welded together as you have described. The single panel takes advantage of internal friction for stiffness. Your layered panels are at a disadvantage in this respect.

5-90's corrugated example could make for a stronger panel, pound for pound than a solid panel. But being able to bond or weld the corrugated ribs at every crossing intersection would make a huge difference. This type of panel could be stronger in beaming strength, but would be at a disadvantage for localized impact strength, .i.e. coming down hard on a pointed rock or stump.

What might make for an interesting skid plate would be cutting board plastic, structurally bonded to a steel backing plate. Maybe throw in a few stengthening ribs on the back side of the steel for good measures.

 

[5-90]

5-90's corrugated example could make for a stronger panel, pound for pound than a solid panel. But being able to bond or weld the corrugated ribs at every crossing intersection would make a huge difference. This type of panel could be stronger in beaming strength, but would be at a disadvantage for localized impact strength, .i.e. coming down hard on a pointed rock or stump.

What might make for an interesting skid plate would be cutting board plastic, structurally bonded to a steel backing plate. Maybe throw in a few stengthening ribs on the back side of the steel for good measures.

Which is precisely why I brought up rivetting the panels - with spacing properly laid out, you can get enough strength for the shear forces to not be an issue, and the compressive load from squeezing the wriggly tin into a thinner profile will increase tensile strength. How much? It would take me a bit to figure it (I need more data...) but it's enough to help out - it will "stretch" the cladding panels to help keep them from deforming, and will reduce the risk of penetrating the belly pan.

I think most wriggly tin has a sectional profile of an inch or so (I'd have to look) but coupling the tensile preload of the compressed sheets (think "flat spring") and the light weight of the composite sheet, with the strength gained from rivetting the panels (I'd probably use CRES rivets to keep the rivet strength in line with the sheet steel (rather than using aluminum.)

This is getting interesting - I may have to give this the once-over with my Materials & Processes instructor this week and see what he has to say. May have to try this myself sometime.

I do like the fact that assembling and rivetting the panel will allow for FULL coverage with paint or coating of choice - if you don't get everything protected, dragging this thing thru ONE puddle will be enough to make it fail soon (rust you can't see is more damaging than rust you can see...)

5-90

 

[Mr.OverKill]

my thoughts behind welding the 3 into 1 is the working against each other idea, if the bottom layer is pushed up the middle will try to push it down and if that doesnt stop the first then the streaching of the second and third should definately be enough to keep it more ridgid, do you understand my thoughts on this or am i wrong in my hyopthisys, i could well be. i believe the layering effect would eliminate the need for ribs and fourmers or reenforcements, oh well just some thoughts for consideration, and i concure the riviting ,even in my design, would be better for two reasons 1st the painting and sealing factor and 2nd rivits done correctly are stronger than most welds, other wise they wouldnt build bridges with them.

you guys make me think, i like that!

Troy

 

[5-90]

Which, again, is where wriggly tin comes in. It's got those nice round curves up and down, and you can compress it like a spring (I'd probably not try to squish it down past about 1/2" high, but that should be plenty) and rivet it with CRES rivets while it's compressed (bring a bunch of buddies to stand on the thing while you're working.)

If you try to rivet one side free and compress the other while you rivet it, it don't do nothing. Once you get the first side nailed down, the other should be easier.

I could figure rivet spacing later for optimum strength.

Difference here tho - the rivets they use for bridges and structural ironwork are solid steel and hot-formed, while we're using hollow "pop" (mandrel-expanded) rivets. This can still work in your favour (you have to get to both sides of a structural rivet!) but you'll have to plan your work before you get started.

The main advantage to rivets in structural steelwork is simple - there is no heat affected zone from rivets like there is with welding (which has to be heat treated to remove, or else you have significant stresses due to the local heating. That's why they keep working toward reducing the HAZ by using MORE heat - more heat, locally applied, can fuse the metal faster and reduce the HAZ.)

It is the "prestressed" aspect of the wriggly tin laminate idea that holds promise to me - I just might have to experiment with this idea. Do I have some sheet metal and wriggly tin out in the shop somewhere...?

5-90

 

[Weasel]

I think I understand what you guys are trying to do and I don't see the point of the laminates with steel. Grain pattern isn't that critical with an plate steel, and your not gaining anymore strength from using thinner layers over a thicker layer since your moment of inetria is what really effects you strength or impact resistance of these plates. MaXJohnson pretty much hit quite a few good points. If you are set on laminates look at using fiberglass, or other composites layers for stiffness and strength. Although with most composites the load would be in the transveres direction placing the fibers in shear and bending which is where they are the weakest. They still might be stronger then steel though. A plastic lower skid may be a good idea and I had considered it untill I talked with Jason Paule about it. Tracy Jordan runs a plastic skid and Jason doesn't think it's worth it. It still hooks on to rocks and ends up tearing chunks out of it along with huge rips and gouges. Also it tends to stick to and get hung up on the rocks in the Black Hills. Jason also suggest that the thickness need to run really didn't save that much over thinner steel, when steel works so well.

Stress risers from the drilled holes won't be a real issue, unless the piece is flexing like crazy then you may get fatique cracks, but a skid shouldn't be flexing that much anyways.

Rivets are fine but only should be used in shear where they are the strongest. Using them on the bottom of a skid plate may not be the best idea since now they are in shear and tension/bending. The tension bending will more then likely cause them to loosen up and then everything will fall apart.

Heat treatments with any mild steel are worthless, don't even worry about it. Warpage is about all you have to be concernded with.

As for the waved sheetmetal, thats sort of along the right train of thought but I don't know if it would really hold up all that well. I think it would bve more apt to deform and spring back then adding stregth which is what you want. You don't want the skid to be flexing much at all. Honeycomb would be a good type of material to sandwhich between a couple sheets of steel and provide some additonal strength but then you get into material costs, how to insert the honeycomb then seal the structure without damaging the honey comb, time to make, time to analyis, ect. PIA, I tried it.

Shape and geometry is where it's at for a good strong, impact resitante skid plate. Here are some pics of the one I'm going to build. Flat with a raised center section. The forward and aft edges will be bent or rolled.

The was my first idea, not the additonal support added in the space under the tranny mount. That bracing has been elminated, but may be added later. I'm hoping the outer supposrts will be enough.

side view of final design

If I had some money and I might be able to snag some material form our composites lab I would run a couple layers of carbon fiber on the top of the skid. I could then the reudce the thickness of the bracing. Or make it out of chromoly sheet then heat treat it, but thats $$$$$$.

 

[bj-666]

what's this going to be made out of 1/4" seems like nothing is stopping it from turning into a U after a few good hits. why did you choose to make a bend in the middle to accept the tranny why not make the bottom flush all the way across, make the pieces of angle iron go from one side to the other and just put a plate on top of them in the middle for a tranny mount.

 

[Weasel]

3/16 or 10 gauge. Side wrap up to the outside frame rail and the angle should provide enough resitance to it wanting to bent into a u. Raised the trammy mount for clearance. If I can get the extra room why not, I'll probably never hit it up that high and the angle pieces don't really to much good in resisting the torsional flex from the tranny, motor, ect right under neath the mount. Light wieght was a pretty big goal.

 

[5-90]

I put another thread up on this after I talked to my M&P instructor last week, with a couple neat ideas. Essentially, it was a matter of coming up with a lightweight filler between the sheets that wouldn't collapse and have its strength wrecked after the first impact.

Find the thread, and let me know what you think. I think I called it "Lightweight Skid Plates," or something similar...

5-90

 

[Roll-over]

Have you ever looked at the belly plates that are on YJ's and TJ's. PIA things when it comes drain time on the tranny and TC but it sure does protect alot compared to the XJ crossmember. I've wondered if one could be adapted to fit an XJ, it already has the tranny spacer and such.

I saw one the other day on a rubicon in a drive-thru. It looks like it offers good protection, but it seems to take up a lot of clearance. I am thinking more like an inverted turtle shell shape. It would be nice to slide an obsticle without worrying about all the crap underneath.

-r0

 

[XJsaabTech]

someone mentioned this steel laminating idea was similar to plywood, so I thought to myself, why not get a few sheets of thinner material, maybe 1/16" or 1/8" and a whole lot of JB weld. Spread a nice even coat of JB on the first sheet and lay on the second, and so on, then park the jeep on it overnight so it doesn't go anywhere, and voiala!! Steel plywood, made to any thickness you like.

 

[Mr.OverKill]

ok, final shot at making my point,

Q:if you put a C clamp on both ends of your leaf springs, will you get any flex or movement?

A: no, it will be as stiff as if you were on 2" thick bars of solid steel, no flex and the layers will work against each other to keep it compleatly solid and if it does flex at all it will be forced by compression of the lower and stretch of the upper springs respectivly back to normal or "A RELAXED STATE "

same theory, lower plate and upper plate keeping the center plate where it belongs through tention and compression. i may be wrong but i think it would work very well. we do the same thing with major structural beams and girders on older naval ships to retro fit and re enforce them after it has been proven the older I beams are flexing beyond limits.

the reason for doing this in the first place is to " make a thin, flat, smooth and strong cross member/ belly pan skid plate combination" all on your own that would be less expensive than a store bought one.

 

[cruzmyxj]

As an A&P mechanic, I like the rivet idea. Although I would probably go with a cold bucked rivet instead of pop rivets. They last longer. Now I know this would probably be more expensive than buying a cross memeber, but what about laminating a thinner layer of steel, a slightly thicker layer of titanium and another thinner layer of steel cold bucked riveted together. My thought being that titanium is lighter than steel and as strong. Also were as steel tends to bend titanium has sort of a spring quality to it. It will bend a little and then return to it's orignal shape. Also to relieve heat stress from welding, what about shot peen. Not bead blast, but actual shot peen. We do this to tianium engine blades after weld repairs on jets. Or there is a place near me that does cryo.