New to Fiberglass, very basic questions...

-Is the weave of the fiberglass significantly relative to the strength of the finished product?
-Do the thicker, heavier weaves produce the stronger parts?
-Can layering the finer weaves result in parts as strong as those made of stonger weaves?

I managed to get a 50m roll of, what I beleive to be, 2 to 3 oz fiberglass very very cheap. I'm making some structural components and I've been buying 12oz fiberglass as needed for those parts.
Could I do just as well by using numerous layers of the 3oz?

Thanks in advance!
Eric

 

#1 Yes

#2 Yes

#3 Possibly

It depends on the type of glass you have, there are many different types of weaves, stitched and chopped glass, plus combinations of these. They each have their use in a laminate, just adding more layers may, or may not, be the correct course of action.

 

I concur with post #2.

The design of the structural parts probably has more to do with chance of failure than your questions do.

Although, the density of fiber vs resin and the direction of fiber vs stress (loading) are important too.

-Tom

 

Thanks for the quick answers!
The fabrics I use (and will always use) are woven rather than chopped. I'm also quite careful in the direction and lay of the fabrics, ensuring that the tensie strength of the fiber is utilized as much as possible. I've produced quite a few good parts so far using the heavier weave, I'd just like to start using fabric off that roll so I can start saving some money.

Follow up question: I've seen some fabrics that have a very tight weave vs some that are looser. Provided I get good permiation into the tight weave, that should be the stronger of the two?

I guess the core question that covers it all is; How much of the flexural and impact strength of the fiberglass is covered by the fibers and how much is covered by the epoxy? 50/50? 60/40? etc

 

To answer the question accurately you would need to supply a composites engineer with the exact type of glass, resin, layup schedule, method of production (hand laid, bagged, infused, RTM), resin content, plus a print and description of how the part will be used.

Or ask one how he would build the part, most likely it would be different than how its currently built.

 

I don't know the numbers but I would think it's a lopsided one, 70/30 or 85/15 or something. The fibers take the load pretty much, the resin transfers the loads to the fibers.

There are different kinds of strong and strength as you touched on with flexural and impact. You can enhance different one's by matching the resin with the cloth. Epoxy and e-glass are kind of mismatched, in that the resin can elongate much more than the glass before it destructs, so your limited by the "strength" of the glass. Polyester and e-glass are much closer together and both are cheap, that's why they're so popular and useful. They give a less flexible product that destructs suddenly when it's limit is reached. Epoxy and carbon fiber give a similar brittle "strength", while epoxy and kevlar are a closer match in elongation, giving a flexural strength that stretches or flexes a bunch before gradually (comparatively) destructing. Epoxy, carbon fiber and kevlar are also much "stronger" than poly and e-glass for a given weight and volume, also more expensive.

All that is very basic stuff that could very well be wrong nowdays, at one time it was pretty close to the facts.

As far as your question about using different cloth, it depends on how close to the edge of failure you are building. It depends on what you're building, how much strength you need, what kind of strength you need, what other properties you need , such as light weight, abrasion resistance, conformity to shape, and how much of a problem is it if the "structural component" fails, as in time, money or injury to other things or people.

 

As I'm new to this, I'm starting fairly simple. I' have a Pelican 160 canoe that I'm outfitting foropen water rowing. What I'm working on now is the forward "cabin cap" structure.
I'm using foam core construction sort of like carpentry, in that I'm making ribs as I would if I were working with wood.

I saturate the fiberglass cloth and lay it out on the rib, laying it thicker where it needs to be stronger (bends, mounting points). Since I have no vaccume baging equipment, I cover the peice in plastic and meticulously "massage" all the bubbles out of it. Once that's done, I use half a dozen jorgensen clamps to squish the whole peice between two slabs of wood where it cures (no oven).

I tested the method by layering four 3/4" thick bits of foam with a layer of 3oz fiberglass between each layer, and again curing it under pressure. It got me the 19oz crossmember:

 

The direction of the strands determine the stiffned direction of the layup. If you have unidirectional strands north to south then it will be a lot stiffer than east to west which will bend quite easily.

To know the strength of the glass layup you have to weigh it and it depends how dense the layup is done.

 

Hi
Ok when you are talking about glass materials you have to be specific as to the weight and type of glass you are talking about .
Its not difficult to understand just some basics !!
Chopped strand matt is made up of radom strands of glass about 50 mm long or so .
The weight usually starts at 300 gram m2 , 450 gram m2 ,600gram m2

No there are woven matts and a big variety of weights and types the heavyer the glass the courser the weave .
You are better to use 1x 600gram than 2x 300 gram !!
Because under distruction the glass will part between the layers !!
There are some issues with using heavyer glass layers !
Do you understand what i am saying ?
You have to see all the differant types of glass matts to understand what anyone is talking about .

And yes the weave of glass is significant and they are many and varied , each one having differant properties to the other for all kinds of aplications and uses . The oriantation of the strands on multi layered matts is another one that people dont completely understand or take enough notice of .
Its not difficult just common sense and a good understanding of whats required .

 

I think we're talking about the same thng, though I was using SAE weights and you are using metric. So my 3oz fabric would be about 100grams x m2, and 12oz would be about 350gram x m2... I think.

I do follow you, and mentioned a few times that I was working with woven rather than chopped mat. I've observed a few different kinds of weave, and I'm not sure what each was called. I can say that what I 'm using is, by far, the most common weave pattern I've seen.

 

Woven is as basic as it gets , but it will use a little more resin for the same weight of glass as a stitched fabric of the same weight . Woven will also have more flex on a flat panel than the stitched fabric because of the way it made ! in small jobs it dosent sound like much but multiply is out in a big job then you start to see the material savings !!
With woven and stitched fabrics there then comes the oriantation of the glass in differant dirrections and multi layered cloths . Chopped strand is usually used as a tie layer between the layers of fabrics to strengthen the resin between each layer .
Unidirectional and light weight chopped strand are really the only 2 products you would really ever need to build almost anything . BUT its the understanding of the glass and which way you want the strength to run and how the product will behave in use once you have manufactured it !!
One company i worked at use 100% chopped strand matt to make everything used on there range of power boats startng at 10.6 metres up to over 16 metres long !! Heavy was a understatement but it worked !!. and thats where a lot of the people in the glassing industry have come from those days . Change happens very slowly . You then get some one that goes completely over board and saves so much weight in the quest for lightness that the boats falls apart .
Remember this = 80%of failures are from poor workmanship and 20% of failures are from bad choice of materials used !!

 

all of my structural stuff, so far, has had a foam core. I haven't used any chopped matt yet becaus I'd assumed it wouldn't be as stron as the woven. So stitched seems like the way to go when strength to weight ratios matter?

As a follow up, last night I got my mix ratio's a bit wrong. The epoxy became much MUCH hotter than usual, too hot to handle, an I had to toss it out. I'm not proud of myself for that one.

 

You are right, csm has not much strength, use it only between woven or uni / multi- directional layers, and use the lighter versions of csm to save some weight. And of course on the outer skin to prevent print through of the fabric weave pattern.

Foam core or (better) Balsa is ok above the waterline when done right. Leave it below!

Are you sure you got the ratio wrong? It sounds more like you have used too much resin in a pot instead of spreading it out.

Regards
Richard

 

...pot life of mixed resin depend greatly on the mass of the mix. As heat is being generated from the mixed catylist, it pays to get the resin out of the container asap. Ice cream containers, being a square box section as compared to say a roller paint try, will set off the bulk resin much faster.

Go to the DIAB web site to see and read about different cloth weaves and strengths and uses.

 

If you are using epoxy the mixing ratio is critical that you get it right . Measure the size of the area x the weight of Glass , know the saturation % of the glass - then you know the amout of resin it will take to wet out that particular amount of glass.
Check the hardener you are using is it fast ? slow ? or meduim? use shallow containers to mix resin in!! .
When the resin is mixed the chemical reaction causes it to get warm then warmer and this warmth speeds up the hardening process to the point where the resin begins to smoke .
Its a chain reaction so think !! mix less resin each time and use shallow containers !! If you still have trouble change to a slower hardener . Never change the ratio of hardener to resin !!! CHANGE THE HARDENER TO A DIFFERANT TYPE !! remember that the clock starts to tick the moment you pour the two together so know what the gel time is and work within that !!!
If you change the ratio then the resin will not react properly and will never reach its proper hardness when it has cured !!
Also dont mix two hardeners to try and make you own formular !!. If you change the resin/ hardener ratios and have a failure its your problem not the resin manufactures !! so done point the finger !!!
If you want a more forgiving resin system to use then look seriously look at Vinylester !! Its much easyer to work with and dosent have all the badness
and sticky messy etc etc of epoxy ,plus it dosent run out of a vertical panel .

To get a nice smooth and light weight laminate use peelply over the top of the job and rolled out properly bleeds any surplus resin through to the surface and when you tear the peel ply off when its gone hard you have a really good looking finished job and it will have compressed the fibres and got rid of any unwanted resin .

Chopped strand matt has a million uses and has been used to make a lot of things !! Its more used with polyester and vinylester resins , There nothing wrong with using it !! every product has its uses just some are better than others !!