Stitched vs woven fabric advantages and disadvantages

[acerox]

Hello Everybody,

I have been coming around this question for a while. I have found a thread about it but I was hoping to get some more ideas.

Why would you use woven fabric instead of UD, for example a layer of woven vs biax (two UD stitched together)? I fail to the see the advantage of woven vs stitched (non-crimp) fabrics.

I have developed a list of advantages and disadvantages. Let me know if I have missed something:

(0,90)-UD Stitched better than (0,90)-woven.
• Better tension and compression stiffness/strength due the lack of crimping.
• Better drapability. Lack of crimping allow better conformance with round surfaces.
• Higher fiber to resin ratio.
• Easy to wet in either hand lay-up or infusion.

(0,90)-Woven better than (0,90)-UD Stitched.
• Better resistance to crack propagation since the crack would be to propagate through the fibers (in an individual layer).
• Stitching may induce fiber fracture in stitched fabrics (I am not sure about this one).
• Better peeling resistance (why would that be? Due to nesting of the plies?)

From a manufacturing point of view, it should take the same time to add a layer of woven fabric than a biax fabric. So not really an advantage there.

I know that a specific aerospace company replace two UD layers 0 and 90 by a layer of plain woven (90,0). So there must be an advantage there, is the better resistance to crack propagation (definitely not a negligible characteristic) the main reason?

Thanks!

(old thread -

https://www.eng-tips.com/viewthread.cfm?qid=355297)

 

[ESPcomposites]

A few comments here on page 12 of the free download.

https://www.espcomposites.com/book/sample.html

Brian

http://www.espcomposites.com

 

[Compositepro]

Fibers can peel out of UD surface plies for several inches or feet away from the damage location. Woven is preferred for a surface ply for this reason. Fibers cannot peel out because they go under a 90 degree tow every 1/8" or so. Stitched fabrics have a stitching thread to hold them together so there is still some fiber crimp that occurs that lowers the compressive strength compared to UD prepreg.

 

[SWComposites]

UD tends to split under impact damage, particularly on the back side, and so typically has larger damage areas than fabric laminates.

 

[acerox]

Thanks all for the good answers. It does seem to be damage tolerance the main advantage of woven versus UD or stitched fabrics.