newbie needs lots of information!

General Composites Discussions Composites Talk
#1

hey guys, first off you have a great forum here. I’ve been reading up and doing a bit of info gathering, but I still have a few questions.

So here’s the back story; I’m a senior in college working towards my BSME, and I have just been assigned my capstone/senior project/whatever you prefer to call it. I was fortunate enough to get on a project I really had an interest in, but the down side is I’m actually working on behalf of a company so I can’t give exact details on what I’m working on. A “stripped down” description is that I’m designing and building prototypes of what I’ll call a “J” shaped carbon fiber ladder wrung , where the sole of the foot is placed in the curve of the “J”, and the straight section is used to secure the structure to a ladder/building/ whatever. So havening that info here come the questions:

  1. can someone point me in the direction of some good reading material for design considerations (affects of weight, weave orientation, ect…)/calculations/stress analysis for carbon fiber and resins? Fatigue calculations would also be handy!

  2. this project is actually a continuation from a group that was working on it last year, and the team decided that infusion would be the best method, which it may be; but I’m not completely convinced that pre-preg couldn’t be a better alternative. So can anyone point me in the direction of some good reading material for pre-preg vs. infusion? Also, I’d love to read about the curing process for pre-preg. The company has a fiberglass shop, and a furnace that they use to cure their parts, but I don’t believe it’s pressurized. will this cause a problem when working with pre-preg?

  3. kind of along #2, I can’t find a decent place that sells small quantities of pre-preg. anyone know a good place a home DIYer can get some?

  4. One of our requirements is to come up with a good crack detection method for cured parts. Given the complex nature of the CF matrix I’m not sure techniques used for metals will work. Any input or suggestions?

Thanks guys, i look forward to hearing what you have to say, and if anything is unclear please feel free to ask.

#2

An autoclave is probably best for something like a ladder rung. But i’m sure it can be done using prepreg and an oven.

Others should have more input than i have to offer.

#3

If the parts need to be tested prior to end-use, ultrasonic testing will work.

#4

good to know. anyone else? please…

#5

You’ll be reading for years. Check out SAMPE journals. Maybe your library has old copies? Ask your ME prof’s if they have any related to what you need to read about. Ask them about books as well.

  1. this project is actually a continuation from a group that was working on it last year, and the team decided that infusion would be the best method, which it may be; but I’m not completely convinced that pre-preg couldn’t be a better alternative. So can anyone point me in the direction of some good reading material for pre-preg vs. infusion? Also, I’d love to read about the curing process for pre-preg. The company has a fiberglass shop, and a furnace that they use to cure their parts, but I don’t believe it’s pressurized. will this cause a problem when working with pre-preg?
  2. kind of along #2, I can’t find a decent place that sells small quantities of pre-preg. anyone know a good place a home DIYer can get some?

Each has their pros and cons. Epoxy prepreg has tack, so you can lay up complicated shapes (like your J rung), and get a good finished part. All you need is either a mandrel (foam, silicone, wax, bladder, etc), and Dunstone heat shrink tape. You can also vac. bag it. Autoclave is not really needed. There are many out of autoclave parts made with prepreg and infusion, that are just as good as autoclave parts. However, prepreg is expensive, and hard to get. Ask around various companies. If they like your project, and you convince them enough, you can get a free roll or 2. Try Cytec, Hexcel, TMI-Inc, etc.

  1. One of our requirements is to come up with a good crack detection method for cured parts. Given the complex nature of the CF matrix I’m not sure techniques used for metals will work. Any input or suggestions?

Thanks guys, i look forward to hearing what you have to say, and if anything is unclear please feel free to ask.

C-scan (ultrasound) is a common method. Check composite journal mags for ads. (Composites World, Composites Technology, etc) There are other ways, like wire and fiber optic sensors. I believe that is still in the prototype and research phase, but I have seen it work on large scale apps, like wind blades.

Good luck!

#6

good info, thanks. I’ll be looking into the ultrasonic testing for sure! thanks.

#7

I’ve heard that electrical conductivity (resistance?) of a part changes with breakdown of the composite structure.

As far as a source of prepreg, perhaps you can approach aerospace industries in your area to see if they’d help? I know Boeing’s factory in my city throws away lots of prepreg every day, maybe they’d be willing to help you out!

#8

It does, but is not continuous enough for good results. Most of the time they coat the fibers with metal, or use carbon nano materials in the resin. Lots of work in that field.

#9

Yeah, we will be looking for something realiable…and cheap, lol. I appreciate the advise so far guys. thanks.

#10

If you need a roll of Dunstone shrink wrap…I think I still have a few donated to my former Plastics job training classes…

#11

i may just take you up on that offer Werksberg.

I’ve been looking round our area for local companies that may have had prepreg scraps, but no luck so far. anyways, i think my team is just going to try the infusion process fist and see if we can get some repeatable test samples. the process itself seems fairly straigh forward, but getting repeatable samples might be a chalange for us.