Would this laminate be symmetrical and balanced?

General Composites Discussions Engineering Talk
#1

Fellow Engineers

Would a layup consisting of an odd number of 2x2 twill fabric (5 plies) be considered symmetrical and balanced?

For example:

[0,90/±45/0,90/±45/0,90]

i have searched the internet but never found this type layup to confirm my thoughts.

any thoughts?

#2

[0,90/±45/0,90/±45/0,90]

A little confusing with the slash and commas… I think I get it though

[0,+45,0,-45,0] would be symmetric and balanced yes.

I consider 0/90 equal in my cutting for the carbon fiber we use. Glass wouldn’t be, or some weaves of CF wouldn’t be equal.

If you had two 45 plys that were both + or -, then it would symmetric but not balanced.

#3

a document on this with some info on symmetry and call outs

http://onlinelibrary.wiley.com/doi/10.1002/0471459216.app6/pdf

I had another document floating around that had good info on call out for laminates… i think it was from nasa but can’t seem to find it now…

#4

As it is a fabric wouldn’t the call out be ±45? and 0,90 as your document states for figure h?
. . . .unless i have misunderstood.

#5

Since the twill weave is not a true 2-ply [0/90] lay-up, and more of a mix of the two orientations, the [0,90/±45/0,90/±45/0,90] lay-up would effectively be balanced, but more info is needed to know if its symmetric. Note that the bias plies will need to be mirrored from the laminate mid-plane in order for it to be symmetric, so [woven/+45/-45/woven/-45/+45/woven] and [woven/-45/+45/woven/+45/-45/woven] would be symmetric. Also note that this is assuming the 2x2 twill woven has the same percentage of 0 and 90 degree fiber on either fabric side (which I believe 2x2 twills do).

#6

Don’t forget, the warp (or fill) is usually considered stronger than the weft as the warp is always under tension while it’s woven. A true balanced layup should take this into account if possible.
JJ

#7

true indeed. We did testing to be sure it wouldn’t make much difference,and it’s negligible in our application. Plus the margin of safety is generous enough to account for this discrepancy. So I get to use +45 or -45 interchangeably for the most part.

[woven/-45/+45/woven/+45/-45/woven] This would be balanced and symmetrical.

if you look at the document, page 800, figure B, the call out is [0/90]s which means the laminate would be 0 ply, 90 ply, 90 ply, 0 ply. if you wrote just [0/90] it would be just two plys.

though i’ve seen variations in call out as well… each shop might do this a little differently. Basically you use what is understood and makes sense in the end. I had another sheet that explained all this much more easily… it’s one of my text books, if I can find it, i’ll take a snap of it. It does a better explantaion than i am doing.