If I have 4 layers of carbon twill to build up laminate how should I lay it down , I mean how to manipulate angles of each layer to get maximum stiffness.
material - 200 grams carbon twill
what direction do you need stiffness in?
You dont use wovens at all if you want stiffness… You use Unidirectional fibres so that they are held straight, and not like an accordian (woven) which has alot more give and stretch. If you want the CF twill for appearance, use it as a final layer. The difference in stiffness is phenomenal comparing wovens to uni-directional fibres…
I though If i lay the CF in 4 layers in different directions it will be stiff all around…
anyway if not please point how I can achieve stiffness in desired direction by operating angles?
Groper - I never tested uni-directional , what about a layer of quadriaxal - they are build from uni directional i guess.
PS. Im looking the essence of Carbon Fiber - not only look but lightweight and stiffnes
It also depends on the actual fiber itself. I’ve used twill like that and it’s made some great strong parts and then used a different fabric that was immensely more rigid. And as groper pointed out, there is unidirectional as well as various 3d wovens. Then the resin system used has a big effect. Some epoxies have higher numbers than others. And then there is the use of core to increase rigidity. And then… there is the part geometry itself. If you have a flat panel vs a hat shape.
And then finally the ply schedule. You can always tweak the number of plys you use to increase or decrease the strength to maximize efficiency. Really the twill you have there looks great but is made to conform to more complex shapes. You could always do a 5 ply stack say. something like 0/45/0/45/0. Just keep the orientations balanced to reduce risk of warp from resin shrinkage. I would make the outer layers that twill, and then use a plain weave underneath to save on the twill.
that’s just my ruff guideline
When i say unidirectional, this includes multi-axial STITCHED fabrics - not wovens. Stitched fabrics are simply multiple layers of unidirectional fibres held in place by stiching cotton or polymer threads so the whole thing holds its shape and doesnt fall apart.
The idea is the carbon fibres need to lay flat in the laminate (---------------), not like an accordian (~~~~~~~~~) which allows stretch and compression as its stressed and elongated.
Woven carbon fabrics are used primarily for aesthetic appearance. Structural carbon fabrics are strictly non-woven for this reason - you wont find any 2x2 twill or 1x1 woven in aircraft wings, wind turbine blades, raceboat hulls etc etc. Seems so many people think that just because its carbon fibre then automatically it must be strong and very stiff - this simplistic view IS FALSE. Its the physical orientation of the fibres, and the fibre/resin volume fraction which has a greater effect on the mechanical properties of a laminate. I can make a stiffer and stronger laminate with e-glass compared to a woven carbon of equal weight, depending on the lamination process and fabric type variables.
You should alternate 0-90 and 45 degrees as you stack up
0/45 4layers should give you a slightly stiffer x vs y. 0/90 would be balanced x and y. Could be wrong.
I always lay my own parts as close to 0/90 or 0/45. Anything else is too complicated unless using uni. And then it’s even harder sometimes.
Completely depends on the axis you want the stiffness in!
When fibres are stressed in tension or compression, they can do the most work when the fibres are perfectly aligned with the stress direction. This of coarse depends on the loading of the panel or part and how this loading translates into stress in the laminate and the direction of the stress paths. Once established, one can then design a laminate schedule which aligns the fibres in the correct direction, and correct quantity, to cope with the design stress. This Is efficient structural laminate engineering.
However, if the fibres do not align exactly with the stress direction, the mechanical properties deteriorate rapidly, most engineering allows for only 3degrees off axis before the tensile/compressive strength and modulus must be reassessed and reduced by a significant margin. The same happens with wovens compared to straight fibres due to the crimped nature of woven fibres.
So if you need stiffness and or strength in a specific direction or plane or axis, the laminate should be tailored with a majority of fibres in that direction. If you need an anisotropic laminate with equal strength or stiffness in all directions, then fibres running in a minimum of 0 , 90, +45, -45 is usually specified. Some hi tech laminates go further and specify 8 directions, although rare. Most structural parts specify a greater percentage in a single direction and are engineered deliberately like this because its more efficient use of an expensive material. Take a carbon mast for example, 70% of the fibres will be at 0 degrees with the remaining 30% split -+45 deg for tortional ridgidity and keeping the 0deg fibers in column.
SO to make some sort of conclusion:\
1.Woven fabric like Carbon twill . plain etc - are good for elastic laminates
- Non-woven , unidirectional , biaxials etc. are for building stiffness
Well thats not how i would put it. instead id say this;
1.Woven fabrics make a MORE FLEXIBLE laminate than Non wovens.
- Non-wovens will provide greatest stiffness and strength possible, in the direction the fibers are oriented.
So going further, such thing like quadriaxial or triaxial etc. is very good stuff for stiff laminate, and it another adventage is that you lay down 3-4 layers in one shot
Yep, Exactly
Basically the stiffness in any given direction is related to the amount of fibre running in that direction. For twill weaves the fibres run in 0° and 90° so the maximum stiffness will be in those directions unless you lay-up material at 45° to balance the laminate.
If the stiffness you achieve is not enough you could then turn to high modulus fibres such as M46J etc. or unidirectional prepreg or both.
If you just want a laminate that is equally stiff in all directions follow a tooling type lay-up i.e. 0° +45° -45° 90° etc.
Stiffness in the z-directon is related to laminate thickness (number of plies). Using a core material can help in this regard.