Fiber Volume Fractions

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#1

What are the typical fiber volume fractions for each of these processes?
Wet Layup
Vacuum Bagging
Resin Infusion
Vacuum bagging + Autoclave
Resin infusion + Autoclave?
Prepreg

I know this has been discussed in bits and pieces but I wanted to get everyone’s experiences in one spot. I am especially interested in vacuum bagging fraction ratios.

#2

These numbers are by no means scientific. It’s what we’ve found from years of lab testing and sometimes just weighing materials before and after making products.

__________Fiber:Resin
wet layup= 40:60 - 60:40
wet w/ bag= 50:50-65:35
infusion= 60:40-68:32
wet, bagged, 'clave= 55:45-70:30
infusion in autoclave= defeats low cost infusion, would squeeze resin out.
Prepreg= 60:40-72:28

#3

Thank you TET!
I made test coupons with a vacuum bag and I wanted to make sure that my fiber resin volume ratios were within industry norms.

For my bidirectional I got 65 percent and for my uni I got 52 percent

#4

Uni should give the highest fiber ratio. Without the crimps of fabric, there’s little excess resin in the plies.

#5

Sorry to revive an old thread but didn’t want to start a new one for a simple question.

I was told that during a wet lay up and vacuum bag, it is possible to pull too strong of a vacuum because you will suck out too much resin from the fiber and into the breather - is that true? Is there ever such thing as too much of a vacuum in ambient atmospheric conditions?

From what TET said, even ideally a wet lay up v’bagging still results in a higher resin:fabric content than the ideally lower resin:fiber content of prepregs.

When I pull my parts (I use 3 layers of 5.9oz 2x2 carbon, wet laid with SP115 + an extra 3 layer spine of the same fabric) under a vacuum, I feel like they are somewhat flimsy considering how much material there is - and I’m wondering if this is because I’m pulling too much resin out and drying the fabric/not properly saturating it

#6

Breather can sponge up some of the resin and give you dry spots… I use a film barrier with perforations between the Peel ply ( I need to use peel ply for my parts) and the breather. I perforate it myself to help control how much resin can be pushed through when the vacuum is pulled down. Not sure how much weaker it would make it as I have not tried to see if it makes a big difference because if I get dry spots it is bin fodder… lol.

#7

I’ve considered using perforated release film between the peel ply and breather but haven’t yet actually bought any. The only brand I looked at so far, carried by fiberglass supply, has very very small holes spaced every 1/4th inch apart - so they are actually very sparse. I was thinking that this setup might result in having a way too high resin to fiber ration because so little of the resin would be able to actually spill out. Hand perforating isn’t an option for me because I’m looking for volume production :confused: .

So really my question still stands - can you pull too strong of a vacuum in a wet lay up that results in too much resin loss? I don’t actually have any dry spots right now, btw. I guess I need to precisely weigh and calculate my current resin:fiber ratio… I’ll get on that

#8

ABSOLUTLY!.. Especially avoiding the use of a perforated film.
As a rule - 60% Vac on lightweight secondary bonding to keep resin in the job. ( With the full vac stack)
There are many, many various patterns and options for perforated film. They are graded in hole density and open area.
The density relates to the number of holes and their spacing/relationship.
The open area is the diameter of the perforations and all the hole areas added up as a ratio per m2 This information is useful for judging how much resin will bleed through and in what concentration.
It’s a balance and with the correct testing you can tailor your perforated film specifically to your job.
Vacuum consumable companies are usually able to supply 2-5m2 as a sample so you can trial their product before you buy a roll.
A cheaper film that works well in a wide range of conditions is Airtech P31. It’s a low temp option for wet lay and is for max 100 deg C post cures.
If your looking for high volume production, then you have a customer that is (I hope) expecting consistent, measurable qualities in what it is your building and a tested, solid production process will help get you there.

I see your using SP 115 resin, this system is not what I would call a structural resin system. You might need to change to a better resin or add some more fibre if your chasing stiffer laminates.

#9

Thanks for the feedback Astute! I’ll be sure to try out the Airtech P31.

As for me using SP115. Definitely not the strongest resin out there but some of its characteristics are important to me. I’m willing to sacrifice 10-15 pct rigidity for those characteristics that are beneficial to me.

I’m going to try a part tomorrow that is 3 layers of 5.5oz with an additional 6 layer 5.5oz spine - I’ll comment back here on how that part turns out. I haven’t yet bit the bullet and bought perforated release film though.

#10

A small correction from my side:

The Airtech film you would like is Airtech WL3900R P31 (the R can be substituted for B, it is just the colour: red or blue)

WL3900 is the film type (low tech low temp film, 121 degrees C or so)

P31 is the perforation style, which can be done on any film (also the high temp films, like A7300)

#11

ditto what Herman and others have said. I always use perforated plastic when doing wet lay up/vacumn bagging. Go to ACP composites and then their online store and they sell the perforated plastic with P3 perforations. It’s a better price than fiber glass supply.

#12

P3 is a bit open to my liking, for wet bagging. Although it can be done. Use no more than 50% vacuum for P3.

#13

Thanks guys! I’ll contact ACP and try and get some samples from them, or at worst buy a few yards of each material and test them myself. Pulling a partial vacuum is too much of a hassle so I guess i’ll stay away from the P3 and go with something less porous.

Thanks again errybody!

#14

Damn, so ACP only carries P3 it looks like. Any recommendations on where to get perforated release film?

Herman, I know you said only use 50 pct vacuum with P3 because it’s so porous - but am I right in assuming that there would still be less resin loss at full vacuum with P3 than at full vacuum without any sort of perforated release film, and just a straight wetted-out carbon+peelply+breather setup?

Thanks!

#15

A few thoughts:

  1. As the fiber volume fraction goes up the thinner the laminate must become…unless porosity increases. Pressing the fibers closer together is the only way to increase the Vf. A given layup with a higher Vf will be less stiff went bent due to its lower thickness.

  2. One of problems with vacuum bagging is that the bleeder/breather continues to wick resin out of the laminate long after it has been fully compacted. This increases porosity and can cause cosmetic issues. The problem can be helped by using perf-ply with less perforated area OR using less bleeder. On thin laminates the use of bleeder can be sometimes eliminated. Peel-ply is often adequate to absorb the excess resin and provide equal vacuum levels across the part. I have also used a single layer of paper towels in place of bleeder/breather behind some heavily perforated perf-plys.

#16

You are correct. Any perf film is better than no film.

#17

  1. Totally correct. When compared to a laminate with the same fiber layup, a laminate with higher Vf is thinner, thus less stiff. That is where things can go dramatically wrong (and went wrong in the past). The lack of stiffness should be counterbalanced by adding more fiber, or some sort of core.

  2. Correct as well. For very thin laminates paper towel could be enough. Car polishing rags are also nice.

#18

Hmmm interesting, thanks for the feedback. I’ve noticed that I can actually wet out my fiber to such a degree (if I use 150mls for 18x14 inchs of 15oz thick 2x2) that I can actually completely saturate the breather I’m using and the part I pull is noticeably more thick.

ANYWAYS ya I’m going to go ahead and buy some different brands of perf release. I’ll get back to you guys in 2 weeks when I get it in and do some experimenting. Thanks for the input!

#19

Ditto on that…

I have had lots and lots of trouble getting the perf I have actually wanted, both samples and full rolls.
It seems that the distributors only stock the products that sell, and not the full range. I have sat in meetings with salesmen, and been promised all sorts. In the end, you might get 1 out of the 3 perf styles you want to try…

It’s frustrating knowing the right product exists, and your local/regional/national distributor will not help you.

Just a word on the super lightweight breathers… If they become saturated, that can also leave a porous finish as the micro air bubbles and resin gas are trapped in the laminate and not carried off by the breather.

Good luck with the testing.

#20

This is why I perforate my own film… It takes a minute or so to do…