Chassis foaming has been discussed a little on the Org, but I thought now that we've got an advanced handling forum, I'd start a new thread to keep up-to-date info all in one place.

Here are a few threads that discussed chassis foaming:
http://forums.maxima.org/showthread.php?t=444409
http://forums.maxima.org/showthread.php?p=5018964
http://forums.maxima.org/showthread.php?t=175429

 

The below discussion split off the SFC thread:

Yeah, I think 8lbs would be much better:

2 LB Density Urethane Foam
(U.S. Coast Guard Compliant Marine Foam)
Free Rise Density: 2.0 lbs cubic ft.
Expansion Rate: Approx. 25-30x Liquid Volume
Buoyancy (flotation): 60 LBs per Cubic Ft.
Parallel Compressive Strength: 40 psi
Tensile Strength: 30 psi
Shear Strength: 30 psi
Flexural Strength: 50 psi

8 LB Density Urethane Foam
Common Applications: This 8LB density foam is extremely hard and rigid, like that of a soft wood. You fingernail can penetrate its skin, however it cannot be dented by hand. Uses include casting, carving, sculpting, sign making as well as areas where an extremely durable and rigid foam is needed for support.
Free Rise Density: 8.0 lbs cubic ft.
Expansion Rate: Approx. 8x Liquid Volume
Buoyancy (flotation): 54 LBs per Cubic Ft.
Parallel Compressive Strength: 250 psi
Tensile Strength: 225 psi
Shear Strength: 130 psi
Flexural Strength: 350 psi

Note the huge increase in flexural strength. Also, note the drastic decrease in expansion, which might be a plus as far as injection into the frame rails. For the fourfold increase in weight between 2lb foam and 8lb foam, the four different strengths go up significantly more than 4x (e.g., tensile strength is 7.5x as strong: 225psi vs. 30psi). Unfortunately, all their foam costs $18.50 for 4lbs, so 4lbs of 8lb foam only covers 1/2 a cubic foot.

98SEBlackMax, how much foam did you end up using for what you did (sounds like just from the front wheels forward)? You said you just poured it in with a funnel, does that mean it's very fluid immediately after mixing?

 

I used the 4 pound density in the front frame rails. Im thinking of doing the mid/rear part of the car in 8 pound density as a sort of chassis tuning. Im thinking if the rear is a bit stiffer than the front it will help dial out some of the car's understeer.

http://forums.maxima.org/showpost.ph...65&postcount=7

http://forums.maxima.org/showpost.ph...64&postcount=1

It starts off as a liquid when you mix parts A and B, after that you only have 20~30 seconds to mix and 10~20 seconds to pour the stuff in. It has an exothermic reaction and starts to get hot when the expansion begins.

Hotter air temps gives you more expansion and saves money, so I would recomend doing this in the summer. Don't even bother in air temps below 50 ~ 60 F.

The frame rails with 4 pound density needed one can of A and B for both sides. I screwed up and poured a bunch in, it ended up leaking out of huge hole I forgot so I had to use two cans of A and B. The center crossmember only needed a half can of the 8 pound stuff.

If you don't have enough in the hollow spaces after a pour just mix up a little more and pour it in, multiple pours are ok. This stuff will find every empty space...

 

Nice, I never saw that thread you posted and it didn't come up in a search. I'll add it to the links at the top. Did you have a lot of urethane mixture left over or did you use it all?

I'm not sure a funnel would work for the main frame rails running beneath the doors since there are no holes above the rails. So some method of injecting the foam would be necessary.

 

The rocker panels you would have to drill a hole and pour it in, Just remove the plastic boot guards (or whatever they are called) and put the holes underneath them. Also you can sand off the excess foam and use bondo to fill any uneven surface then paint it. I did this in the engine bay and you can't even tell I foamed anything.

 

I hadn't thought of that. I assume you mean the plastic door sills? I guess it would make sense that the rocker panels are right below them.

 

subscribing....I wonder what the benefits would be since I already have SFCs......

 

Even stiffer chassis, hard to say how noticeable it would be. If you foamed all the rocker panels/rails including the engine bay you ought to see significant stiffening over the SFCs alone since they don't go beyond the wheels.

Probably the biggest difference you would see is less road noise transmission, which is worth the cost and trouble alone, IMO.

 

Are there any modulus of elasticity figures available for this stuff? That would help tell you how much stiffness was added directly. Indirectly you get a few % increase in the effective OE stiffness, since it helps the hollow steel sections maintain their shape (and hence their stiffness) as loads are applied.

Norm

 

In another thread BEJAY posted a link to a technical paper on chassis stiffening in SUVs, but it wasn't particularly interesting. Other than that I haven't seen any technical data on chassis stiffening but I'm sure it's out there.

 

I guess I might need to try this before I get SFC...

 

Remember if you want to or need to do any welding do it before the foam is installed.

 

That's my concern as it might prevent adding a bar/cage.

 

Yeah. I don't know where to get SFC's from. I guess I will ask around when I move to Gainesville and maybe do foaming in the winter.

 

guys read this article it gets into them using foam on a 300zx they say a chassis can never be to stiff and using 2lb per cubic foot can stiffen the chassis area 40%

http://www.sportcompactcarweb.com/pr..._300zx_part_5/

 

Yeah, that link is included in the threads I already referenced, but thanks for putting it up here.

 

Hey guys I ordered 16lb/cubic ft density foam (the toughest stuff they make) to put in the SFCs. I think this will help with vibrations as well as generally greater comfort from an even stiffer chassis. Plus if I ever need to return my car to stock form because I'm selling it or whatever the reason may be, I can just grind the SFCs off the car, with the foam.

I was also thinking if the FSB is hollow, which I am pretty sure it is. I might foam that as well, when I do the ES FSB bushings.

Lookin for opinions on this idea.

 

16 is tough stuff. I am going to go with 8 when I do it. Also I do not think it will help with vibrations unless you got some AFTER installing SFC. It will help with vibrations if you pour foam into the frame like I plan to do.

 

Well if I did the frame rails.. the car would never be able to be brought back to stock. Which I dont want. Foaming the SFCs will hopefully make it like theres much thicker beefier tubing welded to the bottom of my car, which is only a good thing.

 

I agree with Kevlo, I think foaming the SFCs will help the stiffness of the SFCs and might reduce noise a tiny amount, but it won't give you the noise reduction that foaming the frame rails will.

Still don't understand why you're so concerned about the SFCs and foaming. I doubt any potential buyers would even notice them. Only if they had a shop inspect it the shop might point them out but it's not necessarily a drawback. Are you planning to sell your car in the next couple of years?

 

Not planning to sell but yah never know.

Most people are scared of what they dont understand. Most people dont understand SFCs. I would have to sell this car to a performance minded buyer if I were to sell it the way it is now. I would prob end up taking most of the stuff off before I sold it, but unless it gives me real problems I am planning on keeping it as a daily driver for a while.

As I've said before I agree that foaming the frame rails would make a bigger diference but I'm not interested in doing that. I really am having problems finding a way to inject the foam all the way into the SFCs evenly and I wanted to get opinions on foaming the FSB. Which I believe is hollow.

 

I'm pretty sure the FSB is solid based upon past weights and measures. You could drill a small hole and find out easy enough though.

 

It's not worth the bother to fill a hollow sta-bar. Even if the foam set up as stiff as cast aluminum (E=10E6 psi, which is about 1/3 that of steel) you would not gain enough stiffness to much more than barely notice.

Some stiffness numbers, for comparison, showing that it's a 1% - 5% effect.

25mm solid steel . . . . . . . . . . . . . 19175

25mm x 5mm wall hollow steel . . . 16690

25mm x 5mm wall hollow steel,
15mm solid aluminum center . . . . . 17517

25mm x 5mm wall hollow steel,
15mm soft center (E = 3E6 psi) . . 16938


Norm

 

Very interesting, thanks for that info, Norm.

 

I will find the results from a study that showed structural foam increased the frequency of an object when filled with it. Its on the org but right now I'm drilling the holes in the SFCs and getting them ready to be filled.

 

Well yeah, but he was talking about the FSB, which is about 22mm in diameter (very small) and if it's that small it sounds like foaming it won't help much. The SFCs and frame rails have much more hollow volume and bigger diameters so I can understand foaming having a greater effect.

 

Yeah I didnt read his post fully before commenting. I am kinda running around trying to figure out how to get the foam into the SFCs

 

Foaming works more effectively in larger non-round thin-walled sections than in something like a small thick-walled tube.

Partly it's because the foam represents relatively more of the now-composite cross-section.

But I think the larger effect is that the foam maintains the shape of non-circular sections. Elastic buckling and other local deformation effects within light-gauge structural shapes tend to reduce the stiffness from that which you compute for the overall section with the formulas found in most engineering texts. Foam gives that "lost stiffness" back (at least some of it), so it's a real-world improvement more than it is a simplified numerical one. In a way, it's kind of like seam welding vs spotwelds (metallurgy permitting).

And maintaining the shapes of structural members better cuts down on all those little vibrations that are ultimately noticed as noise.

sciff's comment regarding the frequency is generally correct - frequencies will go up as long as the stiffness increases faster than the mass required to achieve it is added.


Norm

 

So if I got SFCs with 0.120 wall 1.5" round DOM tubing, it's probably not worth it to foam them, I'm thinking. But the rocker panels for sure.

 

For SFCs in that kind of size it's not worth it for increasing chassis structural stiffness, though a case might be made for using it for noise reduction reasons.


Norm

 

Well boys the war has been waged

ME VS DA FOAM

I got owned hard core.. Nothing too valuable was destroyed but when I tried to force the foam down into the tube it splattered everywhere. I am pulling it off my skin, thankfully I covered my car before doing this job, but lets see my costs so far

Cost me 30$ for a cone shaped bit to drill the holes in the SFCs
10$ for the vinyl hose
20$ for the foam
10$ in funnels
30$ for the shorts I just ruined with splattered foam

what does it all equal? an expensive waste of time... Hopefully my 100$ contributes to knowledge that this foam is VERY thick stuff and will not travel down any sort of hose, it barely went through the bottom of the funnel.

So if you want to pour it into a cavity make sure you drill a BIG hole, and dont plan on pumping it anywhere.

 

I thought I made this clear in my previous posts, you CANNOT force it into a cavity. You have to drill holes from above and pour it in QUICKLY. Its about 20~30 seconds when it begins to react and expand like crazy.

 

My contribution; I think this explains and puts more insight on structural foam and NVH.

http://www.abrn.com/abrn/article/art...uctural%20foam

http://www.abrn.com/abrn/article/art...uctural%20foam

 

Interesting read. I hadn't thought much past stiffness with regard to vehicle performance and NVH, but the effect on crashworthiness to the point where it is an integral part of passing whatever applicable crash standards makes perfect sense.

Well worth saving as a Word document. Thanks.

Norm

 

Oh no, Sciff! I thought for sure you would have read the Sport Compact Car thread (linked above in this very thread) where they explicitly mention how messy this stuff is and to wear gloves and not to wear nice clothes...Also, the 16lb stuff has got to be super thick since it doesn't expand much. I was thinking the 8lb stuff would be difficult enough to pour in. Don't give up. I'd really focus on the rocker panels though, just lift up the plastic door sills and drill holes if necessary.

 

Well as far as I can tell, the chassis foam idea has been extinguished. I decided to call my local Infiniti dealership to see if they would foam my car for me. I thought the dealership would be a good place to start because they have to deal with the old Q45s with foamed chassis'. Here's a rundown of what the technician told me
1. Drilling the holes in the exact correct locations would be almost impossible, due to the sectioning of the chassis, similar to the hull of a ship. Without knowing where the sections started and ended, the job would be very difficult to get right.
2. Adding the foam could compromise crumple zones. I know this has already been discussed in regard to the SFCs, and I believe we figured the changes would be minimal.

Regardless, I was told they would not do the job on any car that didn't already have foam from the factory.

Has anybody else made any progress with the foam? I guess my old SFC's will have to suffice...

 

At least you got some technical reasoning behind their position that sounds like it's on the level instead of just any old thing to brush you off.

Norm

 

After getting all the info on foam that I could I have determined that the reason most people dont use it, is because for a street vehicle it is not really practical. As said before it will negate crumple zones, as well as making future work on the vehicle impossible (but if your only putting this stuff in main structural members and those members get damaged the whole car is gonna be scrap anyway) It doesnt make a lot of sense to put it in most race cars because most racing leagues have strict rules which are nor friendly to a foam filled car. Regardless my street terror (the Rx7) is going to get foamed with a couple hundred dollars worth of foam.. I am doing 8lb throughout the car. This will either be the last time I ever spend a cent on foam or it will determine once and for all the effectiveness of this solution.

So far I've just done the rear subframe with a mix of some 16lb I had left over and some of the nex 8lb stuff... So figure it comes out to a density somewhere in the middle.

Check out the pics


2 Part Expanding structural urethane foam




Foamed Subframe with derlin bushings installed









The derlin bushings are pretty much a solid bushing

 

very intresting info

 

It's nice that the tech gave you his reasons but they don't sound like reasons not to foam, even if they are in fact correct. If you foam the whole rocker panel, there's no worry of which sections/locations you must aim for.