0¦/90¦ layup. Is there a difference for a symmetric fabric?

[KirbyWan]

Howdy all,

I'm going to lay up some test panels of carbon fabric with EA9390 adhesive and cut tensile test coupons to compare strength. I'm going to make three panels of 3K-70-PW (8 plies), 3K-135-8H (4 plies) and AH370-5H (4 plies). I was wondering If there is a difference between the 0° and 90° direction for a fabric with the same number of tows per inch in each direction and the same fibers per tow. Should I lay up the panel with all laminae in the same direction? Should I alternate back and forth? If I lay up the panel with all laminae in the 0° direction should the test coupons pull the same if cut in the 0° vs 90° direction?

My intuition is that they should be identical regardless of ply laminate direction and test coupon direction as long as it's parallel to one of the fiber directions, but I wanted to check with this august and knowledgeable forum for their expertise.

Thanks,

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.

 

[rstupplebeen]

In general one direction will be straighter and one more bent based on the tension. It may be negligible but I would make sure before just assuming. I hope this helps.

Rob Stupplebeen

 

[Demon3]

Is there such a thing as a totally symmetric fabric? Unless it is a non-woven material I think there will be variations no matter what.

Chris DeArmitt PhD FRSC CChem

http://www.phantomplastics.com

Consultant to the plastics industry

 

[KirbyWan]

Demon,

There are fabrics like 1581 fiberglass that has 66 tows in one direction and 64 in the other (I'm working from memory so I may be off a bit) but for these if there is a variation, it is statistical and not by design. I am not concerned with statistical variation since I would affect both directions the same (well statistically speaking anyway.)

rstupplebeen,

I figure both directions would be equally bent, unless they were tensioned before cure. This might be a good research subject as a matter fact. The one variation that would make a difference is with a Satin fabric you could decide if you want the outer surface fibers to be aligned with the test coupon or across the coupon.

Thanks for both of your responses,

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.

 

[Demon3]

What I meant is that even if the same polymer were used in both directions, the resultant fabric would not be truly symmetrical around all axes so there would be property variation. Imagine a grid with fibres at 90 degrees, the properties along the diagonal will be different to the x and y axes.

Chris DeArmitt PhD FRSC CChem

http://www.phantomplastics.com

Consultant to the plastics industry

 

[KirbyWan]

Demon,

O.K. I understand what you are saying, and I agree that the laminate properties would be different off axis. This is a well known property of comosites. But for my test I am only concerned about the properites along the 0° and 90° direction which are parallel to the warp and weft of the fabric.

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.

 

[SWComposites]

The warp and weft properties will be different. can be up to ~ 10%. Probably closer for PW, more differences for the 5H and 8H. You should layup the panels with the warp fibers in the same direction. For the 5H and 8H fabrics, layup the bottom half of the plies with the warp side down, and the top half of the plies with the warp side up, to make the layup ~ symmetric. Run tests in both the warp and weft directions.

 

[Compositepro]

SWComposites is correct. In the weaving process, areal fiber weight (AFW)is controlled independently in the warp and fill directions. In the warp it is controlled by a non-adjustable reed. So total AFW is controlled by adjusting the pick-count in the fill. Ideally warp and fill are balanced, but in reality only within certain limits. In some tests you want to measure this difference. In actual structures you want to randomize this variation by switching the warp and fill directions. In many cases this is not possible because a long part can only be made by running fabric in the long direction. In this case you want to measure warp and fill properties of the fabric to make sure that both are in specification.

All of the satin weave fabrics have a warp-face and a fill-face. These are inherently unbalanced, though not necessarily in AFW. If you cure a single ply it will come-out shaped like a potato chip.A single ply of plain weave can be fairly flat. With unbalanced fabric the plies in the lower half of the layup are flipped-over (not rotated) relative to the upper half.

It gets a little complicated so it is important to understand why you do these things.

 

[KirbyWan]

Thanks SWComposites and Compositepro,

Follow on question,

For say the 8H satin I can have either the warp face out or the weft face out. I can also cut my test coupon along the warp direction, or the weft direction. I'm guessing the coupon would be strongest with the warp direction fibers on the outer faces of the test coupon and aligned with test coupon. Does this sound right?

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.

 

[Compositepro]

I'm not completely sure but I think the opposite is true. You have the same amount of fiber running in both directions but the outer plies are subject to extra stresses from the grips so having 90's on the outer surfaces protects the more highly stressed zeros inside.