Fiberglass - multiple layer question

[neond7]

I've only done tip to tip fiberglassing (one layer) on one rocket before, it turned out well. I have a custom project I'm working on that has fairly large fins that hang down, so I want fiberglass them to protect them.

If I'm doing two layers of 5.8 fiberglass, and a veil layer, do I put down all three layers at the same time? By that I mean wet out the first layer, apply the second, wet it out, and then apply and wet out the veil layer. Or do I wait for each layer to cure before applying the next layer?

Thanks!

[dixontj93060]

Personally I prefer to do one layer at a time. Second (and third) layer starts when you still have some tack in the previous layer. For standard E-cloth cut your weave at ~45 degree angle to achieve added strength with multiple layers.

[Eat, sleep, and Fly]

It is all up to you. I personally believe that if you do all of the layers at once, It will be stronger, but again, It's up to you.

[Feckless Counsel]

Neond7,

I'll bet you can do all three simultaneously. Wear several layers of glove to peel as things get sticky. Work epoxy and bubbles from the center first using resin roller and then a squeegee. If the work is not going well then wipe it all clean and try another method.

But, then again, I'm Feckless.

[cavecentral]

I do tubes wrapping one piece of 9oz around for 4 layers at once. Not sure why any othe layup would be different unless you had trouble getting the cloth tp lay where it needs to be.

[rockets4kids]

One thing to be aware of is that if you let the epoxy cure fully you *must* to sand it to roughen the surface before adding an additional layer. Even still, there will be a slight loss in strength compared to a single lay-up.

[Aksrockets]

Doing it all at once shouldn't be too hard. Use an epoxy with a long pot life, peel ply and a vacuum bag set up if you have one. Good luck!

Alex

[neond7]

I just completed the first set, things seemed to have gone pretty good. I made a template and then traced out and cut the sections I needed.

Since this rocket needed to stay light (so I can still park launch it on "G" engines) I decided to only do one layer of 5.8oz s-glass (supposed to be stronger than e-glass) with a veil layer of 1.45oz industrial cloth. I put it to bed with a layer of Teflon peely-ply. T-Fish taught me that trick earlier in the year, it really flattens out the seams and leaves a very nice surface finish. Saves a bunch of sanding later!!! I peel off the teflon when the epoxy is still a wee bit gooey and then trim the edges of the fiberglass. So much easier than when it fully hardens.

Only two more sets to go. Of course then the spot putty and sanding fun begins (insert sarcasm here). Sure wish I had an air conditioned area to work in, a hot garage in Florida is a miserable place to be this time of year.....

This rocket is actually the first of what will be a matched pair. This is an actual LOC IV, I also had enough blue-tube left over from a Polaris upscale project to make a LOC IV clone using some custom cut fins and the nose cone from my Wife's original crashed LOC IV. This one will be mine and named "Red Bird", with the "clone" being my wife's and called "Blue Bird". Mark from StickerShock made some awesome vinyl for them both - can't wait to see it on the rockets!! Good things to come. :-)

[Feckless Counsel]

neond7,

Glad to know I'm not the only guy suffering epoxy on glass. Look great and God speed in your flight.

Feckless

[DRAGON64]

If you are planning multi-layers of glass, then yes, doing them all at once would make a stronger bond then doing them individually. For me though, I generally do one layer at a time, as I tend to work a little slow. The one time I tried a multi-layer lay-up, I worked it so much, that I worked air bubbles into the first layer, and ended up ruining a section of tube. So now I just lay-up one layer at a time. Too this I will add, doing each layer seperate tends to add more epoxy to the build than what it needed, making your tubes a little heavier.

[dixontj93060]

If you are planning multi-layers of glass, then yes, doing them all at once would make a stronger bond then doing them individually.

Not necessarily true. You do not need to apply all layers at the same time to achieve the chemical bond. By applying the subsequent layers after the gel/set time and before the cure time (both published for most decent brands) is reached on the previous layer, the same chemical bond is formed. This along with rotating the angle on the weave of the fabric between layers will achieve a stronger resultant laminate when measuring stress and flex across multiple dimensions.

[ECayemberg]

Not necessarily true. You do not need to apply all layers at the same time to achieve the chemical bond. By applying the subsequent layers after the gel/set time and before the cure time (both published for most decent brands) is reached on the previous layer, the same chemical bond is formed. This along with rotating the angle on the weave of the fabric between layers will achieve a stronger resultant laminate when measuring stress and flex across multiple dimensions.

Getting nit picky here, but I have to add a bit. While I agree completely about strategic alignment of the angles of thread, allowing previous coats of epoxy to "gel" before proceeding to susequent layers will result in using significantly more resin than had the multiple layers been applied while the epoxy was still wet. While the strength may be the same for either method, the mass will be greater for the method allowing the epoxy to set up in between. When comparing two like materials with the same strength; the specimin with the greater mass will have a lower strength-to-weight ratio.

Bottom line, for the vast majority of high power rocketry, it doesn't matter. Much, but not all of what we build is overbuilt. That said, I lay up all layers one after another whenever possible; it saves on material and weight, and given all the other variables are the same, it will produce a higher strength:weight ratio assembly.

Do whatever you are comfortable with; composites applied to rocketry are great, but oftentimes unnecessary.

My $.02.

-Eric-

[DRAGON64]

Not necessarily true. You do not need to apply all layers at the same time to achieve the chemical bond. By applying the subsequent layers after the gel/set time and before the cure time (both published for most decent brands) is reached on the previous layer, the same chemical bond is formed. This along with rotating the angle on the weave of the fabric between layers will achieve a stronger resultant laminate when measuring stress and flex across multiple dimensions.

Many layups fall off of a roll of fabric. I do not see a benefit of rotating the weave, as the angles would be identical. Also you may lose the length of the fabric you if you are laminating an airframe, that is longer than the fabric is wide. Fabric weave I do not see falling into the same logic given to layers of wood grain that can benefit from directional lamination processing.

Also, when you lay up individual layers, you would be sanding in between layers right. I do, so sanding a cured section is common practice. I have never layered a run of glass on an uncured layer, as there is always some sanding that needs to be done to make sure you are adhereing to finer surface. One with no lumps of fabric threads (cat hairs) and epoxy etc. Note: my process is amateurish at best, as I employ no professional methods, nor do I have any quality work areas. I usually did my laying up in the kitchen or garage, depending which ever is cooler at the time. I have since stopped fiberglassing as it is just a plain pain in the buttt.

As stated, being to exact is irrelevant to this hobby as we do intend to over-build. Laminating a speed demon someone would obviously adhere to better practices than I would ever plan to emply in my work.

[dixontj93060]

Getting nit picky here, but I have to challenge that a bit. While I agree completely about strategic alignment of the angles of thread, allowing previous coats of epoxy to "gel" before proceeding to susequent layers will result in using significantly more resin than had the multiple layers been applied while the epoxy was still wet. While the strength may be the same for either method, the mass will be greater for the method allowing the epoxy to set up in between. When comparing two like materials with the same strength; the specimin with the greater mass will have a lower strength-to-weight ratio.

Eric, I am assuming the layup is done correctly, i.e., with vacuum bagging or other means to migrate the epoxy away and remove the excess before moving on to the next layer. If done correctly, there is a very good chance that your final composite matrix would have less epoxy than a single multi-layer application where you have to pull epoxy through two or three layers into a single breather layer.

[CarVac]

You don't have to use only one breather layer. If you put more on it will absorb more resin from the layup, no matter the thickness (assuming the epoxy has not gelled yet).

[dixontj93060]

Many layups fall off of a roll of fabric. I do not see a benefit of rotating the weave, as the angles would be identical. Also you may lose the length of the fabric you if you are laminating an airframe, that is longer than the fabric is wide. Fabric weave I do not see falling into the same logic given to layers of wood grain that can benefit from directional lamination processing.

Laminate theory is laminate theory. The same principles apply with plywood as they do with a fiberglass or carbon fiber matrix.

Also, when you lay up individual layers, you would be sanding in between layers right. I do, so sanding a cured section is common practice. I have never layered a run of glass on an uncured layer, as there is always some sanding that needs to be done to make sure you are adhereing to finer surface.

No. Sanding is a practice done on cured laminate to "open up" the surface so you can get a mechanical bond for the next layer of epoxy. A chemical bond between layers is superior to a mechanical bond and thus if the subsequent layer of material is applied between the gel and cured state, you achieve that superior chemical bond, i.e., no reason or need for sanding.

[dixontj93060]

You don't have to use only one breather layer. If you put more on it will absorb more resin from the layup, no matter the thickness (assuming the epoxy has not gelled yet).

Well sure, you can always use a thicker breather layer. My point is that with more volume of epoxy there is a higher likelihood that you will reach a saturation point at the laminate/release/breather interface making it harder to pull as much epoxy higher up into the fabric.

[CarVac]

The principles used with plywood laminates are not particularly applicable to the typical layups we make, where each layer is bidirectional.

[dixontj93060]

The principles used with plywood laminates are not particularly applicable to the typical layups we make, where each layer is bidirectional.

Although the differences in X-Y strength in wood are greater and thus benefit from a ply structure, a 90 degree weave also benefits from a 30 and/or 45 layup combo. Most importantly this benefit comes in strengthening the cross (XY) tension, flexure and shear which is a benefit to twist/flutter in fins and airframes (although X axis benefit is marginal to none which is no big deal given the much lower risk of compression failure during flight).

[ECayemberg]

Not trying to argue, but I struggle with two items here:

A) Regardless of strength, weight, fiber direction, or any other variables, I personally don't find it practical to apply one layer, go through the time and material associated with vacuuming, then move on to the next layers after a partial cure. I'm not aware of this practice in industry unless there are specific reasons to let the layers actually cure; I don't find it practical to spend several days for several layers....just doesn't make any logical sense to me; sorry.

B) I maintain that less epoxy (or other matrix) would be used with multi-layers applied at once. Why? The "standard" reinforcement is typically E-Glass, which *wants* to soak up epoxy. Applied directly on top of a previous layer of reinforcement, much of the matrix is absorbed into the next layer, largely wetting it out without the addition of more matrix. Even if the previous layer is vacuumed, once green, this "sharing" of matrix no longer occurs. Yes, the matrix will form a chemical bond to the underlying layer, but it will not "flow" in the same body as the gelled under layer.

Again, it's hobby rocketry; do what works best for you. In most cases, it isn't uber critical. But if you're seeking the lightest part/assembly, using the least amount of time, material, and cost, my recommendation would be to apply subsequent layers all at once verses apply, wait, apply, wait, apply.

Oh, to reinforce what Tim said about fiber direction; FIBER ORIENTATION IS VERY IMPORTANT (yes, I'm yelling ). Figure out what forces you're trying to resist, then orientate fibers parallel to the direction requiring increased strength. Composites work well in tension, not in compression, so remember that as well; again composites are WEAK in compression!

-Eric-

[CarVac]

Well there isn't much to do about that. What alternative is there for taking up the compression loads?

Also, rarely is strength the limiting factor: stiffness is, and stiffness is symmetrical in compression and tension until the material starts to yield in one of the regimes.

[dixontj93060]

A) Regardless of strength, weight, fiber direction, or any other variables, I personally don't find it practical to apply one layer, go through the time and material associated with vacuuming, then move on to the next layers after a partial cure. I'm not aware of this practice in industry unless there are specific reasons to let the layers actually cure; I don't find it practical to spend several days for several layers....just doesn't make any logical sense to me; sorry.

Eric, I am sure this is my adopted/bastardized technique and not industry standard. On projects I care about I do vacuum between each layer because I am so god-awful at doing multilayer without getting bumps and bubbles. Measuring out epoxy and hitting target epoxy-fabric ratios keeps weight to a minimum, at least compared to any results I have ever gotten doing multiple layers at a time.

[ECayemberg]

Eric, I am sure this is my adopted/bastardized technique and not industry standard. On projects I care about I do vacuum between each layer because I am so god-awful at doing multilayer without getting bumps and bubbles. Measuring out epoxy and hitting target epoxy-fabric ratios keeps weight to a minimum, at least compared to any results I have ever gotten doing multiple layers at a time.

Tim,

Whatever works best for you; you're projects always come out looking great, so stay the course! Likewise, I don't expect everybody (anybody maybe?) to adopt "my" method; more than one way to shoot a horse...or something like that.

-Eric-

[ECayemberg]

Well there isn't much to do about that. What alternative is there for taking up the compression loads?

Also, rarely is strength the limiting factor: stiffness is, and stiffness is symmetrical in compression and tension until the material starts to yield in one of the regimes.

Good point; I was using stiffness/strength interchangeably when I shouldn't have. With composites, the way to "take up compression loads" is to increase the stiffness on the opposing side. For instance, a composite aircraft wing designed for "normal flight" ie: more positive G's (pull on elevator) than negative G's (push on elevator) will have significantly more carbon tow (or equivalent) on the underside of the spar. In a typical positve G manuever (turn, climb, loop, etc.), the wing wants to fold "up". It is the stiffness of the underside of the spar (now placed in tension) that resists this; while this occurs, the top of the spar is in compression, but does little to resist the force.

With composite reinforcements, the longer the fiber, the higher the strength: maximizing fiber length and orientating the fibers to resist evil forces will give you the stiffest, strongest? structure.

-Eric-