Help Me to Identify a Composite 1

[MadMango]

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."

 

[swertel]

Have you ever done any composite stress analysis before?

Check out MIL-HDBK-17 available for free at

http://assist2.daps.dla.mil

and click on quick search.

Section 3 has steps for design. Section 2 has properties of composite materials.

This web site also has good information for the composite beginner.

http://www.netcomposites.com/education.asp

I'm assuming your ramp is nothing super-critical that since you are a beginner, your design isn't going to kill anyone. So, to add my disclaimer, you may want to source this design/build out to a composite manufacturer in your area.

--Scott
(but you, MadMango, and only you can call me "swizzle&quot

 

[MadMango]

Scott, thanks for the invaluable information and links.

I left out in the above description, that I cannot have openings larger than .63" in the surface of this ramp. This rules out off the self compnets that are used in catwalks and decking plates. "The attempt and not the deed confounds us."

 

[SJLeemans]

Obviously, strength to weight is the critical factor here. I have a feeling, however, that cost is also going to be an issue. How much are you willing to pay for this ramp? What kind of volumes are you talking about?

Your best bet is to call a composites company and have them do the preliminary engineering for you. I was previously an applications engineer for a composites company, and all I did was prepare the preliminary engineering and quotations for new composite applications.

To get the strength you need in such a small envelope, you are most likely going to use a sandwich structure. You'll probably be able to use an RTM (resin transfer molding) product. Do a web search for RTM companies and call a few......

Glass / epoxy with a balsa or syntactic foam core might work. S-glass actually has close to the same strength as some carbon fibers. However, stiffness and core debonding may be a problem.

If you have to go with carbon / epoxy, it could get pricey.

THe website that Swertel gave is a good one to learn enought to converse with a supplier. After that - let them use their expertise to design the product for you.

 

[MadMango]

Thanks for the feedback SJLeemans.

I have been on the phone all morning and have contacted about 8 companys in California. I have gotten some quick responses from these, and I think I am now on the right track.

Thanks all. "The attempt and not the deed confounds us."

 

[HDS]

You should also look at extrusions. There maybe some off the shelf extrusions that will work.

Seems like alot of work for a wheel barrow