Balancing Warp and Weft Face

[Revngeofrobo]

Hello all,

I know it is good practice to balance your laminate orientation angle by making a systematic laminate about an axis.

My question is around warp and weft balancing of a weaved fabric. Is it good practice to go:

up/up/up/down/down/down

or should you balance them in the same way a laminate would be:

up/down/up/up/down/up

Thanks

 

[SWComposites]

What is the fabric weave style?
What are the ply orientations?

 

[Revngeofrobo]

We are using a 8HS 7781 fabric with a thermoplastic matrix.

Layup 1, 8 ply [45/-45]2S
Layup 2, 10 ply All [0]s

I think my confusion is with the definition of warp and weft.
I'm reading the warp is along roll direction of the fabric and weft or fill is along the width of the fabric.
My understanding is the weft is slightly less strong than the warp direction due to crimp or bending in the fabric in the weave. The type of weave used can affect by how much.
I'm also reading about flipping the fabric over UP/UP/UP/DOWN/DOWN/DOWN to balance it and prevent warping during consolidation.

Where do those two things meet? Does the bottom somehow have more weft than the top and so flipping is sufficient to balance the internal stresses and prevent warping?
Is it also good practice then strength wise to have my all 0 laminate be [0/90]5S to balance the warp and weft strength?

Thanks

 

[SWComposites]

Ok, so you are using fiberglass fabric.

An 8HS weave has 7/8’s warp fibers on one side and 7/8’s weft fibers on the other side. With carbon 8HS fabric laying all plies say warp up will often result in panel warpage. Hence the recommendation to layup 1/2 plies warp side up and 1/2 warp side down. However I have never heard of this being an issue with f/g fabric panels.

Yes, warp is along the roll, and weft is transverse (the inserted yarns on a loom). Differences in properties between warp and weft directions can be due to different amount of fiber straightness, with warp tending to be straighter, and/or due to different fiber ends (picks) per inch in the two directions.

The strength of a [0/90]ns layup will usually be between that of a [0] layup and a [90] layup.

S

 

[Compositepro]

Something to be aware of is that on most looms the warp fiber spacing is set by non-adjustable reeds. So fine adjustments to achieve the target areal fiber weight of the fabric must be made to the weft fiber spacing. So there will almost always be a systemic difference between warp and went AFW.

 

[jotunn]

With carbon 8HS fabric laying all plies say warp up will often result in panel warpage. Hence the recommendation to layup 1/2 plies warp side up and 1/2 warp side down. However I have never heard of this being an issue with f/g fabric panels.

Interesting. Any idea as to why this might be? <edit: specifically, "this" meaning the difference between glass and carbon>

I've not thought about it prior to now...but...fiber properties? Glass fibers being isotropic and carbon fibers being anisotropic (transverse isotropy if I'm not mistaken)...(both CTE and elastic constants)?

My experience meshes with what you're saying. I've cared about it with carbon but not so much with glass...but this has been empirical and based on tribal knowledge...never really considered the "why?".

 

[SWComposites]

Carbon fibers have ~zero CTE, and are much stiffer than glass fibers.