Need some tips: bike frame

General Composites Discussions Engineering Talk
#1

This is only my second project using any kind of composites so bear with my lack of knowledge if you can.

I was given a gallon or so of epoxy resin and hardener by a friend a while back, I wanted to know what it was used for, did some looking around, and got hooked on the idea of building my own bike with carbon fiber.

I have settled on the Idea that I want to build a recumbent trike. So far I have tidbits of info on the process from various different sites, people, and articles. I will link to what I have been looking at at the bottom. I am using the build plans located here

http://www.atomiczombie.com/Warrior%20Recumbent%20Tadpole%20Racing%20Trike.aspx

that are meant to be used with welded box aluminum in stead of CF as a guide for building the hardware. Obviously the carbon frame would be a little more filled out than the spindly metal frame is in the pictures.

I have chosen lamination over any kind of infusion or vacuum process simply because it seems like a ton more work and money. I am planning on laminating fiberglass and then CF fabric over a foam form and the aluminum hardware to create the frame, similar to the way it is done in the instructable link at the bottom.

the epoxy resin and hardener I am using are proset 125 resin and proset 226 hardener, if that is of any importance.

My main questions are:

  1. How thick of a laminate would be needed for it to be structurally sound? (150lb person)

  2. I know the resin is “able” to bond metal but how well typically does a resin like this bond between the Carbon fiber/Fiber glass and the aluminum?

At this point feel free to give advice, criticism, warning, whatever. Hey, dismantle my whole idea if you don’t think I should try to do this without some kind of formal training or something. Just let me know.

Thanks in advance for any feedback!

-Nathan

Relevant links

http://www.instructables.com/id/How-I-built-a-carbon-bike-frame-at-home-and-a-bam/?ALLSTEPS

http://www.manytracks.com/Recumbent/Poste.HTM

http://brimages.bikeboardmedia.netdna-cdn.com/wp-content/uploads/2012/10/carbontrikes-carbon-fiber-recumbent-bicycles.jpg

http://www.utahtrikes.com/uploads/utpix/382/picture/sideview.jpg

#2

Just finished welding and assembling the hardware. I’m about to start on the fiberglass, anyone?

#3

To be perfectly honest, it not an easy question to answer for a couple of reasons.

To say how thick/ how many layers is dependent on MANY things eg. where in the frame, what type of fiberglass, what weight of glass, how the frame is shaped, etc.

I would be hesitant to give a figure without knowing the design and doing calculations and that is a lot of work.

I would err on the side of caution and say make test samples and test them and see what is strong enough.

Bonding metal to a resin? What do you want to bond where?

#4

Hi Nathan,

How did you go with this?

I was just going to add that I think it’s easy to underestimate the usefulness of testing and experimentation, and rely too much on calculation and get bogged down in that. Especially since it’s only your 2nd project and you’re looking to fabricate a structural item I’d say that some initial testing is going to help a lot with those questions you have.

Say if you do a test where you laminate 8-10 foam cores with different layups (I just mean single lengths of core, not entire frames!), you will start to get a good idea for the properties of what you’re working with. That first test alone may give you enough information to make an informed decision on what you want to use for your actual bike frame.

I think that for hobbyist types like us, doing all the calculations is probably going a bit overboard… I mean it’s just for a one-off item for personal use. If you are happy with the layup schedule, then I say go for it. But you need to gain some personal experience through testing & making samples before you can arrive at that conclusion.

I hope you didn’t give up on this project!

#5

Hey Nathan,

Cool project…I’m laying up my second composite bike frame right now. The question about how thick to lay up your frame cannot be answered without FEA calculation unfortunately. More important than how thick should the laminate be is the orientation of the lamina. Here is an example of how you would use FEA to analyze the loading and resulting stress and deflection for a specific number of layers and orientation of fibers:

http://www.curtsdesign.com/projects/carbon-fiber-bike-frame-i/analysis/

With regards to bonding in the aluminum inserts…there are complications like galvanic corrorosion between Carbon and Aluminum and the bonding mechanism itself. Using a layer of glass between the carbon and the al will prevent this. I chose to use Titanium for the first bike so I could directly bond. Still the issue of creating a mechanical adhesive bond. Now I’ve removed all metal inserts and bonding and went for an all carbon approach that uses pressed in bearings.

Good Luck, Post some results!

-Kyle-