02GF74
|
| posted on 5/11/08 at 07:49 AM |
|
|
CSM vs woven sheet
Most, if not all, GRP bodwork is made from laid up CSM mat but has anyone made it using woven mat?
Apparently the thinner the glassfibre, the stronger it becomes and having it interwoven makes it even stronger so in theory there is a weight
saving.
Does anyone know the comparison in strength or the weight saved that by using cloth instead of CSM?
|
|
|
|
|
smart51
|
| posted on 5/11/08 at 07:58 AM |
|
|
I'm currently making my non-seven bodywork from woven roving. For the same weight of glass you need half as much resin with woven roving,
saving perhaps 25% of weight per layer for the same quantity of glass.
WR edges splay apart when wetted out so need trimming or grinding flat, where CSM lies down more nicely. CSM fills into corners better and stretches
when wetted so you can pull it and push it to fit contours. WR drapes more nicely when dry but if you pull it in one place, the pull affects the
whole length of the roving.
Beacause of the differences, I'm using woven roving and CSM in different places, where each one suits the application better.
|
|
|
BenB
|
| posted on 5/11/08 at 08:34 AM |
|
|
Woven would end up stronger but then if you're going for strength you probably wouldn't go for polyester resin anyway.
CSM + polyester is commonly used because it's cheap and easy to work with.
WR + epoxy would be much much stronger (but also much more expensive!!).
|
|
|
Mr Whippy
|
| posted on 5/11/08 at 08:47 AM |
|
|
quote:
Originally posted by smart51
I'm currently making my non-seven bodywork from woven roving.
wee cars looking good, keep adding those pics, its a very interesting build 
Fame is when your old car is plastered all over the internet
|
|
|
balidey
|
| posted on 5/11/08 at 08:48 AM |
|
|
quote:
Originally posted by 02GF74
Does anyone know the comparison in strength or the weight saved that by using cloth instead of CSM?
Average person just using WR vs CSM the weight saving would be hardly noticeable on a set of bodywork. I would guess (just a pure guess, but I have
used both) about 5%.
But, if somone had lots of time to spend developing it and using the right cloth in the right weight (remember that not all WR is the same) in the
right orientation with the right resin. And after several trials (and errors) I would estimate perhaps a 15% weight saving.
So, not much. And it would take a lot of time to do it right.
Also remember that WR has a tendancy to leave an imprint on the moulded surface, so its common to lay a very light weight CSM layer first, then the
WR.
There are some really nice materials you can experiment with. I used one a while ago called Dialin. Its a polyester fibre and the fabric I had it in
was a really light weight WR. It laid into compound curves really well, was very thin. Made a nice panel. And as it was so thin it only needed a
surface veil on it, not a CSM first layer.
Just replacing CSM with WR is not sensible IMHO.
|
|
|
nick205
|
| posted on 5/11/08 at 09:14 AM |
|
|
quote:
Originally posted by Mr Whippy
quote:
Originally posted by smart51
I'm currently making my non-seven bodywork from woven roving.
wee cars looking good, keep adding those pics, its a very interesting build
Ditto - been following this with some interest and could do with more pics, maybe a blog too!
I could see something like this really taking off over the next few years. Would be ideal as a 2nd vehicle for short work commutes or parking at the
station etc. 
|
|
|
emsfactory
|
| posted on 5/11/08 at 09:17 AM |
|
|
wr is stronger than csm but only in two directions. You have to put wr on with layers going in different directions to get a uniform strength. Csm
strands going in all directions. i have a book with the strengths in it but I am not sure where it is. If i can find it i'll put up the results.
|
|
|
twybrow
|
| posted on 5/11/08 at 10:24 AM |
|
|
In a nutshell, woven fabrics tend to drape less well, and wet out by hand is harder. As said, they can provide an increase in strength and stiffness
for a given laminate when compared to csm.
If you are really interested, theyre is plenty of literature out there. Try
this. Lots of graphs in there, showing the performace
differences between ariuos laminate types. Also a formula (the rule of mixtures) for calculating stiffness of different laminates.
|
|
|
Mr Whippy
|
| posted on 5/11/08 at 11:12 AM |
|
|
quote:
Originally posted by nick205
quote:
Originally posted by Mr Whippy
quote:
Originally posted by smart51
I'm currently making my non-seven bodywork from woven roving.
wee cars looking good, keep adding those pics, its a very interesting build
Ditto - been following this with some interest and could do with more pics, maybe a blog too!
I could see something like this really taking off over the next few years. Would be ideal as a 2nd vehicle for short work commutes or parking at the
station etc.
hmm my thoughts exactly, I was thinking along the line of a 2 seater miniture classic beetle, built in a very similar way
Fame is when your old car is plastered all over the internet
|
|
|
jimgiblett
|
| posted on 5/11/08 at 11:28 AM |
|
|
My old Phoenix was built with "race light" WR body work. It appears you can have thinner panners with WR than CSM.
The body flexed alot but didnt break. The weight saving was c.25kg. It was very thin and I was amazed that stones didnt punch holes through it. On
a se7en with less body work I really wouldnt bother unless it was for a race car.
My fury has lightweight rather than race weight body work as this is more of a road car.
- Jim
|
|
|
smart51
|
| posted on 5/11/08 at 11:28 AM |
|
|
Thanks for the kind words. More pics when I make more progress.
I have found that woven rovings use a lot less resin as previously stated. 2 layers of 600g WR uses about 1500g of resin per square metre, 1:1 for
each layer of glass and a bit more for the first layer against the mould. CSM uses 2:1 for the first layer and about 1.5:1 for each extra layer so
long as the first is still wet when applying the next.
2x600g WR = 2.7kg/m2 2x600g CSM = 3.3kg.
|
|
|
BenB
|
| posted on 5/11/08 at 11:48 AM |
|
|
It's worth remembering that you can't use CM with epoxy (you need the polyester resin solvents to dissolve the carrier powder). But then
considering the cost of going epoxy you'ld probably also want to spend a bit more and go woven (perhaps even CF).
|
|
|
britishtrident
|
| posted on 5/11/08 at 03:45 PM |
|
|
The mechanical properties of woven materials are anisotropic (higher in direction of fibres) but much more predictable.
The mechanical properties of CSM are isotropic but much more variable.
In short to get the best out woven materials you have to know a bit about the direction of the principle stresses or you can get some odd effects,
with CSM it dosen't matter you expect the same strength in all (in plane) directions but the strength properties will be more variable because
of the quasi random distribution and direction of fibres.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
|
|
|
britishtrident
|
| posted on 5/11/08 at 03:50 PM |
|
|
Beware CF although massively strong in tension it is very brittle --- Kevlar is much more forgiving.
Nearly all structural components that are called CF are really CF & Kevlar or can also use glass fibres in the mix.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
|
|
|
smart51
|
| posted on 5/11/08 at 04:21 PM |
|
|
quote:
Originally posted by britishtrident
The mechanical properties of woven materials are anisotropic (higher in direction of fibres) but much more predictable.
The mechanical properties of CSM are isotropic but much more variable.
In short to get the best out woven materials you have to know a bit about the direction of the principle stresses or you can get some odd effects,
with CSM it dosen't matter you expect the same strength in all (in plane) directions but the strength properties will be more variable because
of the quasi random distribution and direction of fibres.
Whilst this is all true, for unstressed bodywork, it hardly matters. If it can support its own weight without sagging and won't snap due to
vibration, it will probably be all right.
|
|
|
twybrow
|
| posted on 5/11/08 at 11:10 PM |
|
|
quote:
Originally posted by britishtrident
Beware CF although massively strong in tension it is very brittle --- Kevlar is much more forgiving.
Nearly all structural components that are called CF are really CF & Kevlar or can also use glass fibres in the mix.
Kevlar forgiving - you're kidding right?! It's a nightmare to work with!
|
|
|
