are layered Uni carbon and carbon weave similar?
are layered Uni carbon and carbon weave similar?
(OP)
Lets say you have a plain weave carbon fabric and wanted the same anisotropic properties lets say at 0 and 90 degrees but without the downfalls of a weave such as crimp. So you used unidirectional fabric at these specific angles. Would the result be similar but surperior to the weave since there is no crimp and fibers are as flat as possible?





RE: are layered Uni carbon and carbon weave similar?
You are judged not by what you know, but by what you can do.
RE: are layered Uni carbon and carbon weave similar?
It depends. What do you mean by"result"? What is your definition of "superior"?
RE: are layered Uni carbon and carbon weave similar?
His response was A layered fabric of two uni-directional sets of fibers would be rather unusual. They are usually single layers with a few fibers to hold the fabric in position. A typical woven fabric is very different as you should understand by now because of the crimp and the fact that none of the fibers are in pure tension at any time. You would have to pull the fibers flat to have that happen and the weave doesn't allow that unless you are displacing the other fiber into an even longer path length.
RE: are layered Uni carbon and carbon weave similar?
If you are using two layers of unidirectional, this is mostly true. However for the most part the woven fabric will have better peel strength.
Depending on your application this may or may not be a factor.
B.E.
You are judged not by what you know, but by what you can do.
RE: are layered Uni carbon and carbon weave similar?
Regards
Blakmax
RE: are layered Uni carbon and carbon weave similar?
RE: are layered Uni carbon and carbon weave similar?
If you are going to put mechanical fasteners or holes thru the laminate, it is a good idea to transition the laminate stack to all woven material in the location where the holes/fasteners will be. Uni materials do not like to have holes put thru them.
RE: are layered Uni carbon and carbon weave similar?
The first is shear coupling. In isotropic materials direct stresses do not produce shear strains. In any composite with other than 0 or 90 plies the application of a direct stress will produce shear strains.
The second is coupling between direct loads and bending or twisting. One usually does not expect to see an in-plane load produce out of plane twisting, but for non-symetric laminates this will occur. For the mathematically inclined essentially if any element of the matix is non-zero then the laminate will twist and/or bend under direct loads. To prevent this for every ply at a given angle and of a given material must be matched by a corresponding ply at the same distance below the mid-plane at the same angle and the same material. This is termed a [b]symetric laminate.
The third coupling is between bending and twisting, where a pure bending moment produces laminate twisting. Again for the mathematicians this is because the D16 and D26 terms are non-zero. To prevent coupling between bending and twisting you need a balanced laminate where for every ply of a given material at a given distance from the mid-plane there must be an equivalent ply of the same material and at the same distance below the mid-plane but at the opposite angle (e.g. +30 is matched by -30).
Now clearly there is a conflict between the requirements for balanced and symmetric laminates. In practice the coupling between bending and twisting decreases with the third power of laminate thickness, whereas the coupling between direct loads and bending or twisting decreases with the square of laminate thickness, so in practice it is more common to use a symmetric laminate.
Hope this helps.
Blakmax
RE: are layered Uni carbon and carbon weave similar?
Also, a five or eight harness satin weave ply is quite similar to two plies of UD; you should be careful to balance warp-side down on one side of the ply centerline with weft-side down in the other half.
As noted above by berkshire, woven material can exhibit greater toughness. The CAI value for woven laminates is often higher than for UD ones. I have no CAI data for NCF to oompare that. Also, fiber bridging usually gives a higher value of ILSS for all-0° laminates. This course cannot happen with NCF or woven. With multidirectonal UD a lower than anticipated ILSS can be a result.
I have also seen some counter-intuitive behavour from a laminate of mixed UD and woven. Heater mats for a high-temp repair without autoclave pressure caused disbonding between the UD and the woven. Even harness-satin weaves have no 1-direction and 2-direction thermal mismatches. UD certainly does.
A woven laminate (even harness satin) very rarely has any measurable bend-twist coupling, whereas UD (even if NCF) always does if any angleplies are present.
To summarize my and others' above points, the answer I would give is 'Yes, quite often, but usually at the expense of toughness and some other more subtle laminate characteristics.'
RE: are layered Uni carbon and carbon weave similar?
Now clearly there is a conflict between the requirements for balanced and symmetric laminates. In practice the coupling between bending and twisting decreases with the third power of laminate thickness, whereas the coupling between direct loads and bending or twisting decreases with the square of laminate thickness, so in practice it is more common to use a symmetric laminate.
RE: are layered Uni carbon and carbon weave similar?
I would always opt for a symmetric laminate.
Regards
Blakmax
RE: are layered Uni carbon and carbon weave similar?
Some of things to consider:
-If there is double contour in the part, the "better" material may be the fabric. This will depend on the manufacturing methods and amount of curvature.
-From a producibility standpoint, fabrics may be easier to drill (or least the outer layer)
-An outer layer of fabric may improve the scratch/peel resistance
-Damage resistance (such as compression after impact) can be increased by using fabrics (mentioned earlier)
-I think blackmax mentioned this too, but for certain loading conditions/scenarios, a fabric placed on the bond surface may be better than a uni-ply
-Guessing here, but there may be benefit of the fabric for in-plane damage resistance due to fatigue loading. This could be caused by the natural interlinking of the fabric which could resist matrix cracking.
Brian
www.espcomposites.com
RE: are layered Uni carbon and carbon weave similar?
RE: are layered Uni carbon and carbon weave similar?