need info on flexible material max 2mm thick

[oakies]

I'm looking for a durable material that's both flexible (rollable to one side)and rigid (to the other), like a sheet of paper. The surface outline used is no greater than 13 cm (in length) by 5cm (in width). When rolled up (like a piece of paper) to one side, the material should be able to hold 3 to 4 kg. I'm new in this, so forgive my layman approach.

Oakies

 

[orangepeel]

Oakies,

Are you saying that you want the material to be stiff and rigid along one axis, and transverse or perpendicular to that axis, you want it to be very flexible? If you want something like that, I have something like it sitting on my desk. It is a laminate of graphite fibers and a flexible urethane elastomer, with the fibers oriented at + and - 15 degrees to the long axis. THe fibers are stiff and strong, but perpendicular to the 0 degree axis it is mostly a flexible rubber/elastomer, which deforms easier.

Depending on your application, you could use other fibers, or other materials. It appears at first glance that you want a big mis-match with your axial and transverse stiffnesses (EI).

hope this helps.

ldp

 

[oakies]

Dear Orangepeel,

Sorry I haven't thanked you earlier (busy as usual). I read that selling or promoting isn't allowed in the forums. Have u any tips on how i can get a sample of the material you mentioned (I live in Amsterdam by the way)? If not, thanks anyway. Many regards,
Michael

 

[orangepeel]

Dear Oakies,

I may be able to send you a sample, or you might be able to make it yourself, or if you are part of a university or aerospace firm, have them make it. My email address is kfldp00@tamuk.edu. I teach at a university... and am not in the commercial business.

The scraps I have are about .080 inches thick, or about 2 mm, as you mentioned, but since they have been made with graphite fiber, they would hold hundreds or thousands of pounds, if you can keep the stuff gripped. One is at +15 degrees/-15 degrees, and the other is at +5/-5 relative to the long axis.

TO make it: First find out how to laminate (vacuum-bag) a composite....try composites.about.com. Obtain a plain-weave cloth, such as graphite or fiberglass, with a loose weave. Cut a square piece out, parallel to the fibers. Gently pull on opposite corners of the cloth, so that the fibers "scissor". Align the cloth on some reference mark so that you have a (+theta/-theta) laminate. The smaller theta is, the bigger the mis-match between axial and transverse stiffness, and the easier it will be to roll, and the thinner the stack, the easier it will be to roll. With cloth, the smallest theta you may be able to get will be about 15 degrees. Stack as many layers as needed. Impregnate the cloth layers with a two-part urethane resin, about shore A 30 hardness. Finish the vacuum bagging, and let cure under vacuum. After curing debag, and cut to size.

An alternate method is to make a symmetric stack of unidirectional cloth and impregnate the resin.

Since the urethane resin is more viscous or thicker than a typical polyester or epoxy, the fibers tend to get smeared around during impregnation if one isn't careful.

We use a filament winder, and have a large diameter mandrel. If I want a +15/-15 laminate, I wind a +75/-75 band onto the mandrel and apply the resin during winding. After winding, but before cure, I cut the band along a slot in the mandrel, remove the composite and vacuum bag it flat, or fold it for extra thickness (I am leaving out a lot of steps with peel ply & etc), and then cure it flat under a vacuum and in an oven. I can get high quality laminates that way, at any angle I choose, with any fiber that can be filament wound.

Back to your requrements.... it doesn't appear that you will need a 2 mm thickness for the loads you desire to carry if you use fiberglass or graphite, perhaps you would if you wanted to use another fiber.
YOu can click on my username for some of my other postings that may give additional information... I hope this is helpful.

-ldp

 

[Compositepro]

I'm not sure I understand the question but it seems like what you are asking for is similar to the bamboo mat that is used for rolling sushi. It consists of bamboo sticks about 0.060" in diameter that are all parallel and held together with strings that are woven orthogonally with the sticks. This mat is very stiff in one direction but very flexible in the other. You need to select an appropriate rod material and diameter for your application and "string" material. This can then be coated or encapsulated with an elastomeric material.

I'm sure there are companies already making many things like this you just need to find them. One possibiltiy is specialty conveyor belts.

 

[oakies]

Amice Compositepro,

Actually the bamboo example is quite similar to what I need. You can compare the use to that of a shoe horn, only when not used it's supposed to be completely flat. Also the durability should be the same. Somebody told me to head in the aviation direction for that kind of material. I still haven't any clue. Sounds really good, but the material has to have a 'futuristic look' though. I would prefer a ready to use material that can easily be moulded in to shape and so in the long run can be produced on a large scale. I'll be browsing the conveyor belt tip on the internet. Thanks a lot for the reply!

 

[Compositepro]

Corregated sheet metal also posseses a large difference in flexibility between the x and y directions.