Just a thought: A PVC Frameset
 

Just wondering if a PVC-made frameset would be feasible ha ha ha....some carbon have that sound not unlike a hollow PVC,..I wonder if a stronger PVC type material can be made into a lightweight frame??? It maybe plastic but plastics can also be made tough! Any enginer/experts can share their thoughts?

Your question raises another question: Why?

^ actually I just thought of it. There was an advert just a few minutes ago about a new, tougher, UV proof PVC drain on TV and the thought just sprang in my mind. Its cheaper than carbon and I presume unlike aluminum my absorb more vibration. Hell its weight is anorexicly desirable ha ha ha ha...

Just mould your PVC pipes with carbon fiber reinforcing.

well find the right connector pieces and id love to do it :P

I'll bet per foot, of the thickness required for the needed strength, that it is heavier than aluminum.

I think Huffy and Ross already did it. That and carbon steel gas-pipes.

I give you the Itera, cheap Swedish plastic.

http://upload.wikimedia.org/wikipedi...ic_bicycle.jpg

I'm not an enginer, but...

No.

Just NO.

Regular PVC is pretty brittle.

it's been done years ago...a few times.

it makes a fine bike. has it's own characteristics, none of them inspiring confidence.

Can't you use standard steel lugs, or is that cheating?

It seems like it is kinda going about design in reverse. It makes sense to identify a material with superior mechanical properties (titanium, certain grades of steel and aluminum, composites, beryllium, etc.), and then determine how best to utilize it in a frame to harness its properties. But PVC is just kinda flimsy and has no particularly desirable properties, so it wouldn't make much sense from a design perspective to "make it work." Raw, I would guess based on practical experience that it would make a usable but not very good frame, either being too heavy to obtain the desired strength or being too flimsy to obtain the desired weight. The way you could make it stronger is to reinforce it with fibers or particles, as in the case of carbon-fiber (which is carbon-reinforced plastic) or metal-matrix composite, but that has already been done with better matrix materials than PVC.

I'm a materials enginEEring student (senior so I have a little credibility). Carbon fiber parts are a fiber reinforced plastic. The typical plastic being used is epoxy. Carbon itself is extremely stiff (modulus of elasticity is about 700 GPa compared to Reynolds 531 which is like AISI 4130 steel has a modulus of 205 GPa {when normalized to 870°C and air cooled.}) and an extremly low density (1.78-2.15 in fiber form, compared to 7.9 g/cm^3 for a high strength steel.

Now the problem. Carbon itself is EXTREMELY brittle. Think of pencil lead. Same stuff really. However, if you make the fibers small enough, then there isn't a large enough internal bending moment to fracture the fiber. Its the same principle for fiber glass (truly just normal silicon glass that is made extremely thin.) In essence, you can not fracture these fibers by bending them, however, you can bend them easily so thats not the best for supporting human life with. However, in the direction of the fiber length, it can support a lot of force. In a perpendicular weave orientation (typical looking checkerboard style) you can support a lot of force in both directions and when the force is applied at an angle the vector is resolved to each direction in the fiber.

Now there is epoxy. It is not really stiff, nor light. However, pre set, it flows alright at normal temperatures (I work with it a lot with the only protection being rubber gloves because the stuff is kinda messy) so it can impregnate the carbon weave relatively easily by using vacuums. Once set, it holds the carbon weave in place. In reality, this is the major role the matrix plays. Using more only decrease the specific strength of the carbon fiber composite (makes heavier without increasing the strength) Lately companies (easton is a big leader in this) have been using carbon nano tubes in the matrix to displace some of the epoxy (use less epoxy) because the CNT's are less dense then the matrix they displace.

In a composite, many times the strength of one material is reduced and weight increased, (carbon) while the flexibility of the other is reduced (epoxy) to create a material with a compromise in strength and weight. Looking in my old Callister intro to MSE book, there is a great figure that shows this however, I can't find the same figure online (figure 15.9 for any one who's ever taken intro to MSE and used this book which almost every intro MSE class does) The result is a material who's specific strength is multiple time higher then steel.

Now why not PVC. PVC alone is weak, brittle, worthless for structural purposes. Now could it be used as the matrix of a composite. Yes, and strength could be increased. However PVC is a thermoplastic that has a processing temp around 400*F/200*C. Heating a liquid to this high is expensive, and makes it much more difficult to work with. Epoxy is a product of mixing two liquids resin and hardener together, and within about 8 hours (less if baked) become a solid. This makes it much easier to work with. Thats not to say carbon fiber and thermoplastics do not meet. I do materials testing for an auto-company. One of the things I see a lot is impregnating tiny (as in you cant see without an SEM microscope) carbon fibers into plastics to increase their electrical conductivity.

And before anyone jumps on me for saying blah blah blah, I am simply giving a very brief overview of composites. The science behind them is pretty interesting.

Sorry, but creep, tensil strength, and stiffness all vote no.

Metal matrix composites are composites that use metal as the matrix, not polymers. Examples of this would be putting something like silicon carbides into a liquid phase metal to increase the fracture toughness, stiffness, ect.

I think you'd have a problem with vibration too, PVC can be made stronger, but it's still really flexible

I've known a few HPV builders who made rough drafts with PVC. Mostly to get the geometry right and have a physical form to improve on. They didn't ride them. Joints would be made much like Calfee's bamboo bikes.

........er... what? pass me the bong dude.....

could've just said pvc is brittle by itself dude

Hmmmm..... Where abouts are you studying?

Just reminding you that all structural steels have a modulus of elasticity of 205GPa regardless of whether it's normalised steel, annealed steel, quenched steel, Mild Steel, Carbon Steel, CrMo, Reynolds 531, Columbus Spirit etc etc

I don't think the purple primer would be very OCP unless you masked and/or stenciled it.

When I wrote "that" I was referring to composites generally. My point was "that" (i.e. composites) have been done with better matrix materials than PVC -- namely, resins/plastics and metals. It would make no sense to try to make PVC work by reinforcing it when better matrix materials have already been developed.

(I also have a BSME '97 with a materials-science specialty and worked quite a bit with composites in school and in engineering)

Well, according to the stiffness discussions, this is a benefit. All the energy being used to flex the frame will get put back into forward motion or some such thing...:D

you can make a bike stand from PVC...

http://www.instructables.com/id/EB6KT4AYQHEYVZDYSH/

http://www.instructables.com/files/d...Z96.MEDIUM.jpg