Designing form for strength (structural mechanics?)

General Composites Discussions Composites Talk
#1

Hi. I’m looking for references info material on how to design composite structure shapes to be strong in certain directions, to resist buckling etc achieve our design goals with less material.

How to form and curve our composites, molding on beams and other types of structural support to achieve the desired result.

For example I-beams, girders, structural ties, rods, compression members, trusses, cantilevers, thin shell structures and so forth.

What is the area of engineering that deals with the field?

Ideally I want a book on references of common structural forms. I’d like to see a diagram with different variations of the same principle. I’d also like to see a short theoretical principle of how the forces are handled and some brief theory to outline in which direction certain pieces of the structure needs tensile strength/compression/rigidity/elasticity and so forth and what the major failure points are.

#2

Do you have a background in mechanical engineering? Shapes are shapes no matter what the materials.
But designing thickness and radii is very different for composites compared to metals. Designing the specific ply schedule is a job in itself after the shape has been determined, and is where strong knowledge of composites comes into play. You won’t find too many other people on this or other composites forums that really understand the scientific side of these materials.

#3

research the strengt and stiffness needed.
research the directions of the stress.
research the material properties.
do the calculations :wink:

I can’t help you, just starting to do some basic steel constructions, haha. Lots to learn :wink:

#4

I finished Technical university-mechanical engineering in a field of applied mechanics and I can tell you there si no way to learn and understand it from day to day. You will have lot to do just to learn designing parts from isotropic materials (metals etc.). Composites are even far worse to design and simulate. My final work at school was to simulate ply layup on my carbon fiber bicycle frame and it was hell. I dont even say that I made it with correct results. You can read some rules of thumb but thats all you can learn quick. You can also use tons of softwares, but if you dont understand how things work, what you can neglect etc. all you will find out will be useless garbage.

#5

I do not have mechanical engineering background. But I am an engineer and picking up new information, finding relationships within that data and making it useful for myself is something I’m entirely capable of.

At this point I am not looking for the full theoretical background on how to build composite simulations. I’m merely seeking for a head start instead of what I’ve been doing the past weeks - deducing all the relationships myself. I’m also looking to pick up its vocabulary.

The most useful information source would be a reference book suggestion. But I’d also be thankful for other reference pointers.

#6

I’m a junior in Mechanical Engineering, with an interest in precisely what you are talking about. I wouldn’t say I’m anywhere near to be able to design a composite part, however. You won’t be able to understand how to design composite parts with out first understanding simple shapes made out of simple isotropic materials with simple loads that don’t move. Therefore, I would suggest doing that first. As for references… textbooks aren’t typically the easiest reads, but these are two that I used in class.

Meriam and Kraige: Engineering Mechanics – Statics, 5th Edition, John Wiley & Sons, 2002.

James M. Gere: Mechanics of Materials, 6thEdition, 2004, Thomson; ISBN:0-534-41793-0;

Get the basics of statics first(first book) then look into solid mechanics(second book). Essentially, statics explains the loading of bodies that don’t move and solid mechanics describes how materials react to those loads.

Once you’ve got that figured out come back and I’ll have more prerequisite material for you to check out. :wink: Unfortunately, there isn’t really an easy way to understand this stuff…

#7

If you want a book about composites with lots of examples and calculations from real situations (calculations for levers, helicopter blade, vessels, shafts etc.) you can buy a book called Composite materials-Design and applications by Daniel Gay, Suong V. Hoa and Stephen W. Tsai by CRC Press-2003. I dont know if its still possible to buy it.

#8

thanks Mike! I feel like a lot of the composites books I have looked at lack effective examples. I have just bought myself a christmas present. Having a mechanical engineering degree, do you feel like the material was stuff that required a good bit of study to understand?

p.s. I purchased the book from amazon… I guess a second edition is out now.

#9

I’m a Naval Architect and we obviously had to study Structural Analisys. I also had some Composite Materials subjects. And, after doing my Naval Arch. degree, I also studied part of a BEng Yacht and Powercraft Design, at Southampton Institute (UK).

Some of the books that we used at Southampton had really good examples, with keel design, plates, and even sandwich structure. You might be able to buy some of those through their website (www.solent.ac.uk).

Good luck!

Now, my personal advice: study “normal” design, study basic composite properties, and then do some tests on your own so that you can see how fiber orientation and resin ratios affect the test parts (make simple plates and small light beams).

Cheers

#10

fleish it is a must if you want to design parts, layups etc. No way to avoid it. If you want to make cosmetics parts of course you can just guess layup, add layer next time etc. But for structural members - no way. If you dont want to find your self in prison very fast… Its no fun when you can kill somebody or at last cause serious injuries.

#11

There is no way he would go to prison for building anything, but a concealed bomb in a composite case.

edit.
Maybe in some draconion corner of europe

#12

Pretty sure he’s talking about designing/building a product with liability for injury.

#13

snocutt okey, maybe he will not go to prison, but does it help you when you know that somebody died because of your bad calculation? And you told him that your product is 100% safe? You can read several cases of designers/engineers suicides… but this is out of topic. Sorry.

#14

Many thanks for pointing me in the right direction! I’ll look at some of the recommended books/references.

#15

May be as simple as searching for compression/tension testing for specific fabrics. Alot of which are carbon nowadays. Down side is as soon as the epoxy blend changes a whole new model for comp./tens. will be needed. Liability ends with a well written disclaimer…still won’t keep you out of court.

#16

Sure, I’ve been making the cosmetic parts for a while now. At this point, I just want to make some structural parts for myself (so really, I’m the one who doesn’t want to get hurt or killed). I just got that book in the mail, haven’t really got into it yet, but it looks like a wonderful source that will be a great addition to my engineering bookshelf. I will add my impressions of the book to this thread after I finish it.