Radius Bridging Issue

[goyo0812]

I need your help
Now i am struggling with radius bridging issue on ramp down area of C type as follow

This part is made by hand layup using CFRP fabric prepreg.
Now what i am trying is to enhance consolidation by applying compation for each ply.
Each compation time takes around 10minutes under -28inHg.
I don't know if what i am doing is right or not.
Please give your advice regarding radius bridging issue.

Thank you

 

[Compositepro]

Bridging is caused by lay down technique and cannot be solved by vacuum compaction. Vacuum will clamp the fabric at the edges and prevent it from slipping to conform to the contour. The fabric must be pressed into the contour before it gets tacked down on either side of the contour.
Often the best technique is to tack the prepreg down on one side of the radius and create a bulge in the fabric that mirrors the radius. Then tack it down on the other side of the radius before pressing the bulge into the radius. This insures that there is enough material between the tack-down points to conform to the radius without requiring ply slippage to prevent bridging. Doing this to excess will cause wrinkles in the fabric during cure.
The key principles to bear in mind are that fibers do not stretch, they can be compressed slightly by increasing the waviness in the weave, fabric can stretch on the bias by scissoring and causing a corresponding compression on the orthogonal bias, and that ply-slippage is often more limited than might be hoped.

 

[goyo0812]

Compositepro Thank you very much for your sharing valuable information.
Could you please check below article?
this article said that "Fibre bridging may be reduced by using rollers to press the fabric into the corner or by incorporating slip-lines into the layup. However, especially in the latter case this will complicate the layup and increase manufacturing times"

http://aerospaceengineeringblog.com/autoclave-variability/

Do you have any idea of using roller to reduce radius bridging?

Thank you

 

[SWComposites]

What is the angle and radius at the corner where you are getting bridging? How many plies are laid up in the corner? What is the specific ply material and ply angles? Is the part autoclave (pressure level?) or vacuum cured?

 

[cpinz]

There are silicone plugs to use on edges in order to apply locally the pressure necessary to avoid fibre bridging.

 

[Compositepro]

Rollers can be a useful tool for reducing worker fatigue but do little by themselves to prevent fiber bridging. Bridging is controlled by lay-down technique whether using rollers or fingers. Fingers can feel where fibers are bridged whereas rollers cannot. Splices (I have never heard them called slip-lines) are commonly used in building composite molds but less often in structural parts. "Pressure intensifiers" (silicone plugs), pre-shaped to the radius, are very useful for tight radii.

 

[goyo0812]

Dear. SWcomposites

Angle is 172degree, Total plies are 44plies and this material is CFRP fabric
this part is cured in Autoclave.

Dear. Compositepro and cpinz

just before, I got a good result by adding addtional filler plies to radius area.
I will keep posting when other result comes out.

Thank you all.

 

[SWComposites]

An 8 deg ramp angle is quite low so should not be having a bridging problem, though that is a fairly large number of plies. Is the bridging gaps/resin pockets near the tool surface, or distributed thru the thickness?

What is the tool material? are you getting excessive tool expansion during heat up?