Help me to Identify a Composite
Help me to Identify a Composite
(OP)
I cross-posted this to the Composite Engineering forum as well.
I have been tasked with designing a ramp, and I have strict criteria that I have to meet. Due to these criteria, I don't believe that I can achieve this design with conventional sheetmetal or metal construction and think only a composite structure will work.
The ramp is 33.75W x 23.63L, with a max thickness of .50 inches. The ramp will see a max load of 770lbs in the form of a wheelbarrel/wheelbarrow. I am not allowed to have any supporting structure, except at the top of the ramp where it will be hinged with a piano hinge. This allows the ramp to be folded away. The environment will be outdoors, where it can be subjected to Arizona heat, Florida humidity, Wisconsin winters and everything inbetween. Oh, and I forgot to mention that it can't weigh more than 25lbs...
Since I know the material Unobtainium doesn't exsist, I am hoping someone from this forum may be able to point me in the proper direction in what types of composite materials I should be looking into. This would include a realistic thickness (I'm thinking 1.00" min) and weight.
I have been tasked with designing a ramp, and I have strict criteria that I have to meet. Due to these criteria, I don't believe that I can achieve this design with conventional sheetmetal or metal construction and think only a composite structure will work.
The ramp is 33.75W x 23.63L, with a max thickness of .50 inches. The ramp will see a max load of 770lbs in the form of a wheelbarrel/wheelbarrow. I am not allowed to have any supporting structure, except at the top of the ramp where it will be hinged with a piano hinge. This allows the ramp to be folded away. The environment will be outdoors, where it can be subjected to Arizona heat, Florida humidity, Wisconsin winters and everything inbetween. Oh, and I forgot to mention that it can't weigh more than 25lbs...
Since I know the material Unobtainium doesn't exsist, I am hoping someone from this forum may be able to point me in the proper direction in what types of composite materials I should be looking into. This would include a realistic thickness (I'm thinking 1.00" min) and weight.
"The attempt and not the deed confounds us."





RE: Help me to Identify a Composite
The piano hinge would be out, but it may meet your other criteria. It could be hinged with round stock running through the slats and that would allow it to pivot out of the way.
Another option that come to mind is the grating made of fiberglass, I believe, and it is perforated with square hole throughout. This is available in many thicknesses and square hole dimensions.
RE: Help me to Identify a Composite
"The attempt and not the deed confounds us."
RE: Help me to Identify a Composite
Fiberglass grating is too thick for your criterion.
I think that either high-strength aluminum or steel will work. In either case, use a diamond tread pattern or mix in some grit in your coating to make it non-slip.
See http://www.gatorramps.com/ and http://www.mcmaster.com/ for ideas and materials. For the latter, search 'dock plates' and 'anti-slip floor plates.'
RE: Help me to Identify a Composite
I'd use steel plates over a wooden core if that meets your climatic requirements.
Cheers
Greg Locock
RE: Help me to Identify a Composite
The .50" thickness is the max thickness dictated to me by my wonderful Marketing Department (theu would rather see .375"). My brain is telling me it has to be closer to 1.00" thick.
Steel over wood core: I'm an absolute novice when it comes to composites. Is there going to be an issue in applying a finish to the steel, like powder coating the composite plate?
"The attempt and not the deed confounds us."
RE: Help me to Identify a Composite
I should add I haven't designed anything like this - our solar car was composite obviously but all point loads were taken via aluminium plates which then fed them into the composite structure. The point loads from the wheels would worry me on this thing.
Your 25 lb limit is pretty tight by the way, but if the point load issue is OK then I get two 1.2 mm plates of steel with a 10mm core should be a good place to start.
Cheers
Greg Locock
RE: Help me to Identify a Composite
Polyuretane foam is used for insulation for refrigerators, and can be injected through a small hole. You can change its density by changing the components mix.
You could form nerves on the steel sheets that form the box, or weld some omegas between both layers prior to close the box, to add rigidity.
sancat
RE: Help me to Identify a Composite
We don't have any experience with injected anything at work, so I am not sure the injected polyurethane foam is something I want to get into.
I think the quickest thing to assembly will be some turnkey material that I can get purchased at the size required. If it has to fit into a frame, that will be easy enough.
"The attempt and not the deed confounds us."
RE: Help me to Identify a Composite
Cheers
Greg Locock
RE: Help me to Identify a Composite
The kind of foam I speak of, is so tough like cork. The one we use industrially here has two outer layers of aluminum and is 6 inches thick. It is used as walls for big cold-storage plants. However a small portable machine is used to inject this foam when making refrigerating appliances, the machine mixes on the nozzle the components, and they expand and glue to the walls.
But if foam is not the way to go, and my numbers are not wrong, a 0.9mm thin (gage 20) sheet sandwich, with a corrugated gage 20 layer below with waves 1 1/2 inches wide, and 3/8 high could work (as <<ham>>).
I would use glue on one of the sides, and spot weld the other (upper side/contraction side welded). Locally we glue with SikaFlex, but there should be a number of alternatives there.
If my numbers are not wrong you will have a 3.6 kg/mm2 which is very low. The corrugated sheet waves should be close enough so that the wheel cant fall between two of them.
sancat
RE: Help me to Identify a Composite
MadMango:
You haven't mentioned cost. If it's not important, can I join your company please?
Assuming you can spend a bit, the aerospace industry has good aluminium skinned honeycomb composites. Because the honeycomb cells are orthogonal to the surface, they have high compressive stiffness which is what you need to prevent buckling. The loadings are difficult to model but manufacturers will give the data. There are also carbon fibre skinned Al honeycombs - pricey.
Failure mode is something to be considersd. A wooden plank creaks and groans before it breaks - the more sophisticated a composite structure becomes, the less warning it gives.
You'll have to think about point loadings if you're using thin-skinned composites. Also tolerance to damage and abuse. Dynamic loads may be present.
All in all, I agree that 1/2 inch sounds a bit marginal unless it's used in a very tightly controlled environment.
Cheers - John
RE: Help me to Identify a Composite
The modern stuff is kevlar/glass/epoxy of the same general construction - the aluminium hex being replaced by a Nomex core which is a kevlar paper hex.
Cheers
Greg Locock
RE: Help me to Identify a Composite
Well, I've been on the phone all morning and have contacted about 8 companys in California. I have gotten some quick responses from these and am in email contact with 3. You have all led me onto the right track for now.
Thanks all.
"The attempt and not the deed confounds us."
RE: Help me to Identify a Composite
Speedy
"Tell a man there are 300 billion stars in the universe and he'll believe you. Tell him a bench has wet paint on it and he'll have to touch to be sure."
RE: Help me to Identify a Composite
RE: Help me to Identify a Composite
http://www.handi-ramp.com/Portables.htm
RE: Help me to Identify a Composite
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