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glass/ carbon to epoxy/ resin ratios?
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tomoore1 View Drop Down
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    Posted: 20 Feb 10 at 11:59am

I just finished reading a chapter for uni about rock deformation (bear with me). This got me thinking, in rocks the stronger minerals take the load until sufficient strain is reached to deform them. The strain nescessary is determined by the relative abundances of these minerals.

Now applying this to boats, glass (fibres) are strong but brittle. They give a boat rigidity and strength. So, could say lasers be made stronger and stiffer with an increased glass/resin ratio? This would mean that the when you got a strong impact, the boat would fracture instead of deform? On a more detailed note, would the stresses induced by flexing over waves result in microfractures in the glass so drastically reducing stiffness of the older boats?

What about carbon fibre, I always thought that to be flexible. Is it the epoxy which gives it the stiffness? Now, a concept which is very old in high performance archery. High quality arrows are produced by bonding an alluminium inner core to a carbon outer. I know this has been used in masts, but how about hulls? Could carbon/glass mixtures be the way forewards?

Sorry about the essay, its just quite interesting IMO.

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alstorer View Drop Down
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Posts: 2899 		Post Options Post Options   Quote alstorer Quote  Post ReplyReply Direct Link To This Post Posted: 20 Feb 10 at 12:57pm
epoxy fibres have high tensile stiffness (modulus), but the resin matrix works with the fibres to create higher flexural stiffness.

Generally speaking, as you go to higher laminate technologies, you decrease the resin content. Wet layup tends have a lot of resin, then infusion techniques, whilst pre-pregs can be 35% or less resin by weight- note that this is a general trend, and not absolute. It's very hard to decrease resin content in wet layup and infusion.

There's other factors at play- expensive prepregs can use expensive tougheners in the resin matrix system, which dramatically improve the ability to withstand flexure and impact without damage.

Lasers though- aren't they chopped strand glass polyester? There's a heck of a lot could be done to improve both their stiffness and fatigue performance, even without making them lighter or (out of the box) faster.
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Posts: 318 		Post Options Post Options   Quote foaminatthedeck Quote  Post ReplyReply Direct Link To This Post Posted: 20 Feb 10 at 2:20pm
Originally posted by alstorer

epoxy fibres have high tensile stiffness (modulus), but the resin matrix works with the fibres to create higher flexural stiffness.



I'd agree broadly with the rest but I don't think that epoxy fibre would be that stiff, that why generaly glass/carbon/etc fibres are used.

To answer the orignial question the properties of the material use to make lasers could probably be improved slighly by changing the production method and significantly by modifying the consistant materials. However I'm not conviced it would be teribly cost effective.







Edited by foaminatthedeck
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alstorer View Drop Down
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Posts: 2899 		Post Options Post Options   Quote alstorer Quote  Post ReplyReply Direct Link To This Post Posted: 20 Feb 10 at 3:56pm
It's not that the epoxy (or other resin) itself is stiff. It's the composite of the epoxy and fibre that is stiff.carbon fibres are, as mentioned, not that stiff in dry form. Glass fibres similarly.
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Posts: 6660 		Post Options Post Options   Quote JimC Quote  Post ReplyReply Direct Link To This Post Posted: 20 Feb 10 at 6:31pm
Until you start getting into vacuum bagging and so on its generally fair to say that you want the lowest resin to fibre ratio you can achieve whilst still wetting out all the cloth. However ass resin is generally more expensive than cloth I'd be rather suprised if they don't have as low a resin ratio as they can achieve with their standard building techniques without generating too many QC rejects.
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Posts: 99 		Post Options Post Options   Quote tomoore1 Quote  Post ReplyReply Direct Link To This Post Posted: 21 Feb 10 at 7:50pm

Originally posted by JimC

ass resin

Whats this? ok so although the ratio will affect the stiffness and failure type. So how about using say PVC strands with epoxy. The PVC would allow flex while the epoxy is nice and stiff. What restricts which material 'takes the strain' and which deforms?
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JimC View Drop Down
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error

Edited by JimC
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foaminatthedeck View Drop Down
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Edited by foaminatthedeck
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Posts: 452 		Post Options Post Options   Quote ham4sand Quote  Post ReplyReply Direct Link To This Post Posted: 21 Feb 10 at 8:55pm
? i swear its the other way round? whats the dfinition of
"toughness". arent the fibres all floppy when dry,
basically material you could make (very itchy) clothes
from? when the resin dries it goes hard, providing
"stiffness" whilst the fibres are load-bearing?

am i barking up the wrong tree?
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alstorer View Drop Down
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Posts: 2899 		Post Options Post Options   Quote alstorer Quote  Post ReplyReply Direct Link To This Post Posted: 22 Feb 10 at 7:04am
PVC has low tensile stiffness. Epoxy can be stiff but very brittle; less brittle epoxy is not so stiff

As I understand it (sorts of), part of the way that a fibre/resin composite gains stiffness is that the resins bind the fibres together. When the laminate is then loaded in flexure, the fibres are constrained with respect to one another. The Fibres on the outside of the bend become loaded in tension. If there was no resin, they would simply slide against the fibres to the inside of the bend. Because they can't, and because glass and carbon have good tensile modulus, the bending is resisted.
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