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First I'd like to introduce myself, I'm Julian from Lotz Carbon, some might know the brand from former days when I produced saddles, seat clamps and stuff like that. Lotz Carbon is just some kind of hobby, mainly I'm studing mechanical and process engineering at Technical University of Darmstadt in Germany.
So, after trying two times but with little success, I now decided to take another attempt in building a road bike frame. And ofcourse I have to build a new bike using that frame . As you might have read, I will post news about that in my Blog. The poll I startet a week and some days ago was in favour of german as language for the upcoming articles, but I decided to write short summaries if there are interesting parts or selfmade parts. The lack of information written down in english may not be that big, I've been here quiete often the last two weeks, so of course I will answer questions and read comments that are postet here. In addition some of the needed parts are not determined, so I will probably need your help choosing the right ones .
(That's an early design, I can't show the final version yet, that would be boring )
Have fun with the project!
I have just one question (if you already know the answer to it): how much should the frame weight?
I'm already working on my third frame (topic "Berk PROTO-TYPE 3")and my aim is to make a SUB 1000g frame...I know that it's possible to make it even lighter, but I want to make a stiff frame. What's your aim?
1- You say that you used a very simplified FEM model to facilitate the analysis. Do you know of any program where you can take into account all the isotropic properties of the carbon fiber and do the FEM analysis consecuently with that? I know that CATIA can handle anisotropic materials but I don't know if you can define all the options of the lay-up
2- What are the forces that you use for the FEM analysis? I was looking for some data in the EFBe page but I couldn't find anything
3- Do you where I can find the software that you use to know the laminate parameters or something similar?
About the weight of that frame, I don't know it exactly, because I don't which fibre volume content I'll get. I also have no idea how the dropouts will look or what weight I have to calculate for the lugs (perhaps you know from your expierience?).
But the tube set will be around 450g (without lugs, dropouts, cable stops, headset...) if the fibre volume content is about 0,6, the stiffness shoud be good (I do not have any numbers on that, but the layup is similar to other light frames (Storck, Simplon...) and the fibres are stiffer.
With a little luck I'll perhaps get a low-6XXg-frame, but more likely it will come in at 640-650g.
@Epic-o: I used an old version of CosmosWorks the SolidWorks module. This also is able to handle anisotropic material data, but it did not work the way I tried to operate it... But I also had problems to define the properties in the right planes for every tube. A seminar for this software would have been great, I think .
Concerning the forces, I used those Syntaces uses on their red monster for the forces which affect the bar, 1300N on the pedal for sprints (Smolik told me that the force there is about the same in N than the power produced in W, so I went with that rule of thumb), some other forces from EFBe (the documents are only available in German):
http://www.efbe.de/efbedown/Deutsch/Pru ... etritt.pdf (fatigue, riding out of saddle (climbing, sprint))
http://www.efbe.de/efbedown/Deutsch/Pru ... Sprung.pdf (fatigue, jump)
http://www.efbe.de/efbedown/Deutsch/Pru ... ewicht.pdf (fatigue, driver's weight)
http://www.efbe.de/efbedown/Deutsch/Pru ... Sprung.pdf (excessive load, jump (used stage II))
http://www.efbe.de/efbedown/Deutsch/Pru ... _Pedal.pdf (excessive load, pedal (also used stage II))
http://lcblog.lotz-carbon.de/index.php? ... basteleien
Sorry, no english summary today, I'm in a hurry. But I think most is on the Pictures
Mr.Hyde wrote:@Berk, I think I know your topic, I've posted there . You really do a great job, beautiful bikes and a lot more output then I have
Thanks! About the weight, it seems very promising!
Unfortunately I can't see the photos? But anyway, keep the good work going!
Ich verfolge dein Projekt..
http://www.lcblog.lotz-carbon.de/index. ... basteleien
Today with a summary which is almost as long as the article
Mr.Hyde wrote: @Epic-o: I used an old version of CosmosWorks the SolidWorks module. This also is able to handle anisotropic material data, but it did not work the way I tried to operate it... But I also had problems to define the properties in the right planes for every tube. A seminar for this software would have been great, I think .
Finite element analysis of composite parts is actually quite difficult. Most codes (AKA programs) don't handle anisotropic materials well. They may let you define the materials properly, but indicating the reference direction (the 0-degree direction) has always been quite a challenge. Only a few codes are good at this.
Nastran has long been dominant in composites-dominated aerospace, largely because there are a wide variety of tools for indicating material direction. A few other codes are catching up, though. I'm an ANSYS user, and I've been quite pleased with ANSYS' new composites tool, ANSYS Composites Prep/Post. ABAQUS has a composites module that looks reasonably good, though I haven't played with it myself. There are also some code-independent tools (e.g., FiberSIM) for "laying up" your part; you then import your "laid up" mesh into whatever FEA tool you like.
Different engineers like different FE codes, and they can get quite passionate about their preferences. Personally, I'm not like that. I like ANSYS, and I know it well, but you can do a perfectly good analysis in any reasonably sophisticated code. Unfortunately, CosmosWorks is not especially sophisticated. If you can get your hands on a different code--especially one with a composite materials preprocessor--I'd highly recommend it.
Another thing to keep in mind is that your material properties are probably optimistic (unrealistically high). Most composite material properties are determined via tensile tests of unidirectional or woven plies. The test specimens (AKA coupons) for these tests are typically cut from flat plates. The problem is that flat plates are very easy to manufacture.
A frame like, say, a Cervelo S3 is typically laid up by hand into a female mold and then autoclaved under pressure. This introduces a huge number of variables. There are a vast number of in which the real-world frame can deviate from the FE model. Voids, resin pools, errors in fiber angle and material condition all contribute. The result is that the FE model is an idealized form of the real-world part--and to a much greater extent than would be true for a part made out of, say, 7075-T6 aluminum.
I worked on one project that involved a carbon-fiber riser bar. In the prototyping stage, we were designing the bar to survive a 1000 lbf (4.45 kilonewton) load applied in the grip areas. The parts we got back from the factory failed with a standard deviation of 20%. That is, some of them failed at 1200 lbf and some at 800 lbf, and a few bars failed at higher or lower loads. This is a much bigger variation than you'd get with an aluminum bar.
Applying FEA to composites is still worthwhile, but it's important to understand the quirks. And as with any FE analysis, you'll need to validate your model with physical testing. An unvalidated FE model is a dangerous thing.
If I can answer some questions about FE modeling of composite structures, I'd be glad to do so. This looks like an interesting project; good luck!
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