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Omega21
09-13-2002, 09:09 PM
Does anyone know of any information sources for people who are new to composites? I would like to know more about designing layups for certain calculated stresses, and how to determine what stresses to calculate in the first place. I already have done a bunch of fiberglass repair, so epoxies, layup, resins, gels etc etc I'm already familiar with. But how many layers of what cloth with which resin will stand up to how much pressure applied in which direction....I'm completely lost.

I've downloaded the Diab Sandwich guide, but it moves very quickly to being way over my head. Eventually it will absorb into my thick skull and I'll get it figured out, but is there something a little more beginning designing friendly?

Thanks for your time!
Todd

:)

H2Onut
09-13-2002, 09:11 PM
Go to www.fgci.com


they have an 800 number tech line. TALK TO PAT, he knows his potatoes!

Omega21
09-13-2002, 10:25 PM
Thanks for the link...those guys are a wee bit less expensive than the people I've been buying from. I'll have to try them out.

As far as Pat goes..I'm glad to know he's there. But I was thinking more along the lines of a book, videos, website etc etc.

Thanks!
Todd

H2Onut
09-14-2002, 12:19 AM
Well sooner or later TECHNO will read this, He is a good source for technical manuals.

Go here to this webiste, it has links to EVERYTHING nautical


http://www.boat-links.com/boatlink.html#top

DaNut

Techno
09-14-2002, 07:38 AM
You want a simple how many for xxx stress thing but I don't think it exists. About the closest you can come to this is comparision. Something uses 4 layers of 8 oz cloth. If kevlar is so much stronger than glass then you could figure out the reduction. I don't know how you would do it from zilch since you have to do all the stress calcs from the git go.

If all you want is how much stress glass will take, thats all over the place. The difficulty is figuring out how you calculate it. Like a grade 5 bolt. I forgot but say its rated for 50,000psi. For what? 1" diameter? A 1/4" bolt and a 2" bolt both grade 5 don't have 50 Kpsi strength.
Once you figure the unit stuff then it should be "easy". All the man made composites are strong in tension but not in compression. Wood is a good example of a compressive strength composite. So the direction is always in the strand direction. Home built planes use the bias cloth to change this stress direction. I think this means the strands are 45* to the roll instead of 90*. When they pull it off the roll the strands are going 45* to the wing instead of across it and with it.

Heres a link though that goes into too much detail like you wanted. You can pick what you want.online book (http://www.marinecomposites.com/)

There was another I guess I didn't save. It was a commposite industry thing. Did a search on google you would have to refine it but there might be something there.Google (http://www.google.com/search?hl=en&ie=UTF-8&oe=UTF-8&q=composites)

One real easy way though is to build something and test it. West systems mentioned testing a bolt pullout that a company requested. They only wanted to use enough wood to mount the bolts. They epoxied a bolt into wood blocks and pulled them out. When the bolt broke it was too much, they settled for a pull out that provided the strength the maker needed.

Also to confuse all this is the shape of the part and the stiffeners that it has!

Omega21
09-15-2002, 01:40 AM
Techno-

Thanks for the link to the online book, it's exactly what I was looking for! In actuality, your page with your STV is what got me going down this rabbit trail in the first place.

To clarify a little, I've got an Omega 21' daycruiser. To help with being the slllloooowww, wallowing, loamy pig that it is, I'm going to do a little bit of motor & pump rework to it over this winter. I'm aiming at approx 550-600 hp with a new jet pump. Knowing the basics of what makes things accelerate faster, I'm looking to remove some heavy pieces (especially the furniture and the floor!) that are made from 5/8 ply, 3/4" ply & 1" solid teak and replaced them with lighter foam cored pieces. At this point, I'm not planning to attempt foam cored stringers, but a distant family member used to be a composites engineer. I may have to drop by & say hi to the long lost cousin.

Once again, thanks for your help.
Todd

Techno
09-15-2002, 08:47 AM
I would think several times before taking out wood stringers. I don't think the savings is worth the risk. It probably would end up weighing the same.
I think a pretty rough estimate is 1/2 the weight for the plywood. Whatever all that wood weighs its about 1/2 that. More for you since its bigger wood.
I found my hull weighs in at about 560lbs with the 20+lb floor. Rigged should end up about 1100-1200 lbs.
A 2nd battery is 50 lbs which is probably the floor and seats that I reduced. Not much in my case.
Another possibility is stuff like a hammock instead of an actual bed. Check out a helicopter sometime for extreme weight counting. Tubular chair frames and webbing, patio furniture! I'm surprised they don't clothe them in silk instead of cotton uniforms.

captcarb
09-15-2002, 11:17 AM
If a material is rated for 50,000 psi or pounds per square inch, then that is the rating for any diameter. A one inch bolt has a greater cross sectional area the a 1/4, or more square inches. The shear strength of the 1 inch would be greater than the 1/4 by the difference in the cross sectional area. To find the shear load capability multiply the shear strength in psi times the cross sectional area of the bolt.

I would think the Experimental Aircraft Assn might be able to supply the design information about composites. Their members build a lot of composite airplanes. They have a lot of design information in their library.

Jim

ryan_L6
09-16-2002, 08:52 PM
your talking about engineering type formulas .people go to school for yrs to learn all that. they do exist, however, you need to know all the specifications of the material you are using first. compressive strength , tensile strength , coefficiant of thermal expansion and such. I think you would have to contact the manufacturer to get these kinds of specs. If they want to give them to you . Or boeing aircraft has something called bms specs (boeing material specs). but the list is quite extensive . they list things like bms 9-8 type 1 class 4 . like i said the list is quite extensive and includes mostly materials that would not generally be used in boat building. In the meantime , check out this website , i think i remember seeing some formulae on it and they sell a ton of books . www.netcomposites.com there is a ton of info on this site dealing with all areas of composites. hope this helps. if you can get the bms spec of a material you are using, i may be able to pull up info on that material and mail it to you.

ryan_L6
09-16-2002, 08:57 PM
try this one too . go to tech tips . they have some formulae. too complicated for me . i never was good at math.

www.abaris.com

SteveO
10-10-2002, 06:54 PM
http://www.ap-iabooks.com/Compositebasics.htm

Composites basics by A Marshall. It's directed toward composite aircraft building, but has sections on calculating loads.

Alan Power
10-13-2002, 07:35 PM
The rule is, scantlings rule for fiberglass boats,
try this link http://www.macnaughtongroup.com/scantlingsglass.htm

Alan Power
10-29-2002, 01:20 PM
The book, Elements of boat strenght for builders, designers and owners. Available from bruce roberts yacht designer.

Alan Power
10-29-2002, 01:48 PM
The book, Elements of boat strenght for builders, designers and owners. Available from bruce roberts yacht designer.