Subject: Re: [harryproa] Re: masts
From: "Peter Southwood" <peter.southwood@telkomsa.net>
Date: 11/3/2006, 11:57 AM
To:
Reply-to:
harryproa@yahoogroups.com.au

Hi Mike,
Fair enough, I am in a similar position, as a machanical engineer, but with some background in composites which is unfortunately largely forgotten.
However, at the risk of opening my mouth to change feet, I will comment.
If I remember correctly, the matrix (resin) is generally stronger in compression than tension.
Carbon is strong in tension, and in compression if sufficiently supported in column.
Depending on the resin and fibre it is possible for either to fail first as the load increases. Both must have the same strain, as there is no slip between martix and fibre, so the one which reaches its strain limit first will fail first. This may be different for tension and compression.
It is frequently the case that the fibres can withstand greater strain before failing in tension than the matrix. When this happens the matrix develops lots of microscopic cracks, but the composite generally holds together and does not lose a great deal of strength or stiffness, but may lose some chemical resistance. The same magnitude of compressive stress/strain may not cause the same cracking.
So my guess is that the crackling noise is the matrix failing under tension. This can happen long before the ultimate failure of the laminate.
Maybe somone can explain better?
Cheers,
Peter
----- Original Message -----
From: Mike Crawford
To: harryproa@yahoogroups.com.au
Sent: Friday, November 03, 2006 5:23 PM
Subject: [harryproa] Re: masts


  ;-)

  I have a degree in structural engineering, but not in carbon masts.  Let's call it an educated guess.  Food for thought, at least.

       - Mike



Peter Southwood wrote:
Mike,
Is this something you know or something you guess?
Cheers,
Peter
----- Original Message -----
From: Mike Crawford
To: harryproa@yahoogroups.com.au
Sent: Friday, November 03, 2006 4:03 PM
Subject: [harryproa] Re: masts

Peter,

  The point about matching strains is a good one, but I believe the carbon's modulus is magnitudes higher than that of the epoxy matrix, so we won't likely see a failure from the carbon stretching past the epoxy's limit.  This would be especially true with epoxy, which has a bit of give to it.  Case in point: look at how much the upper section of the Rare Bird mast can stretch and flex without any sort of failure. 

  My guess is that the failure would occur from the resin being compressed past its limit.  Since the carbon is very strong under tension, we probably won't see a failure on the windward side of the mast, which is being stretched as it bends away from the wind.  The leeward side of the mast is the opposite, though, being compressed by the same mast bend. 

  As strong as carbon fiber is in tension, as with any fiber, it's nowhere near as effective at resisting being compressed along its length.  While the resin will help keep the individual fibers in column, and they'll be able they can carry some of the load in compression, the resin itself will take a lot of the compression load as well.

  This is a likely point for failure and cracking.  The carbon fiber will keep the windward side taut, and prevent the resin from stretching past the point where it will crack, but it won't be able to provide the same support in compression.  The force will eventually buckle the resin matrix.

       - Mike



Peter Southwood wrote:
Hi Rob,
I dont see why the resin should crack because the carbon is stiffer. If the resin cracks it is because it is stressed beyond its maximum strength. The stiffer the fibres, the less likely the resin is to reach failure strain before the fibres. More likely the resin cracks because it is too stiff for the fibres and does not have a matching strain at failure.
Cheers,
Peter
----- Original Message -----
From: Rob Denney
Sent: Friday, November 03, 2006 7:23 AM
Subject: Re: [harryproa] Re: masts

G'day,
Yes, but the stiffer it is, the more cracking there will be.  My understanding of this is that the noise is the resin cracking as the carbon is so much stiffer.  With glass and kiri, there may be less cracking, or it may just happen at a higher load.  Regardless, I think you will get plenty of warning.  Maybe test a piece of kiri and glass by bending it until it starts to crack, then see how much more it will take before it is visibly damaged.  This may give you some idea of how far you can go past the cracking stage.
 
regards,

Rob 
----- Original Message -----
Sent: Friday, November 03, 2006 1:13 PM
Subject: Re: [harryproa] Re: masts

Rob,
 
Is composite glass/kiri?
 
Doug
 


Rob Denney <proa@iinet.net.au> wrote:
If it is composite, you will hear a lot of creaking and cracking before it breaks.  I would work on one of them doing the lifting as in a capsize you will probably have dumped one of them.
 
regards,

Rob
----- Original Message -----
Sent: Thursday, November 02, 2006 12:13 PM
Subject: Re: [harryproa] Re: masts

Robert,
 
I'd like to sense a failure ahead of the crack, split whatever, so as to salvage the mast and simply add more glass around the outside. But that would be a fairly satisfactory level of strength if they - cause there are two of them - raise the hull.
 
Doug

Robert <cateran1949@yahoo.co.uk> wrote:
Easy enough to check if the masts are strong enough. Load them up by
trying to lift the ww hull with a 100kg weight sitting on it.
I was looking at the characteristics of quality bamboo section and it
looks considerable better than glass weight for weight with 4GPa
youngs modulus and a breaking strain of 30kg/mm 2. It may be worth
considering for cheap masts. I am considering it myself for skinning
cores in areas where exra stiffness is wanted without the expense of
carbon. Hope carbon becomes more easily available and cheaper as it
is by far the best material.
Robert
-- In harryproa@yahoogroups.com.au, "Robert" <cateran1949@y...> wrote:
>
> --- In harryproa@yahoogroups.com.au, Doug Haines <doha720@y...>
wrote:
> >
> > Hi,
> >   
> >   Just meant swinging around on the water, like anchored in the
sea
> breeze comes in 20knots.
> >   
> >   I was wondering about general ideas about swinging around
coming
> from experienced multihullers out there. Like when you anchor a
> bigger boat out further where the wind is. What about two anchors
30
> degrees apart?
> >   
> >   Mast is same as boat - kiri strip and glass.
> >   I've tapered the tops to half dimensions. There is a round pole
> up a metre and a half into the mast that slots in the hull. I hope
it
> is all not going to break.
> >   Obviously it is heavy but is cheaper.
> >   
> >   Doug
> >   
> >   
> >  
> > Myriam & Youri <wangka@s...> wrote:
> >        
> >
> >     v\:* {behavior:url(#default#VML);}  o\:* {behavior:url
> (#default#VML);}  w\:* {behavior:url(#default#VML);}  .shape
> {behavior:url(#default#VML);}        st1\:*{behavior:url
> (#default#ieooui) }                Dear Doug,
> >   
> >   
> >     Dear Wangkas,
> >
> >     
> >
> >     Nice pictures and all, but where is a finished sailing boat?
> >               We know it takes a long time, but sometimes we have
> other worries on our minds … like carbon spars for classical yachts
> where we have to sort out two boats, masts, booms, sprits, poles
> etc,  we have to make molds and plugs for rudders, keels and bulbs,
…
> for the carbon parts we are achieving and testing  a construction
> method VAPM (vacuum assisted pressure molding that gives us
autoclave
> quality laminates (not only on the voids ratio but also on the
> compression side) in our pressure molds( compression +-5 Bars)
which
> can produce one piece parts, which is not possible by standard
> autoclave procedures. We are also currently testing a method for
> direct CNC mold cutting for parts construction …
> >
> >     Also, what do you hope to acheive with around beam?
> >
> >      They are not only rounded in length but also elliptical in
> section and will be constructed VAPM… less windage, better stress
> distribution, less wave interference …
> >
> >     Thanks again for your mast section, it is coming together.
> >               We are glad, how are you going to construct it ? …
> >
> >     The boat really swings around at the moment without masts up
> and I wonder if it can be helped? More a question for the cruising
> boaters - do you plan doing cruising Elementarries?
> >               What do you mean with swinging around ? I suspect
we
> will but that depends on the interest shown … for the moment we
have
> some asks for quotes from France, Switzerland and Germany …
> >   
> >   
> >   Best regards,
> >   
> >   
> >   Myriam & Youri
> >   Wangka bvba
> >   Belgium
> >   
> >   e-mail. info@w...
> >   web. www.wangkaboats.eu
> >   
> >   
> >   
> >
> >     
> >
> >     yaendenboom <wangka@s...> wrote:
> >
> >     Dear people,
> >
> > Our site has been updated.
> > We kindly invite you to have a look at:
> >     www.wangkaboats.eu
> >
> > Suggestions and criticism is welcome at:
> >     info@w...
> >
> > Thank you very much,
> >
> > Myriam & Youri
> > Wangka bvba
> > Belgium
> >
> >
> >
> >
> >
> >
> >
> >   
> >    Send instant messages to your online friends
> http://uk.messenger.yahoo.com 
> >
> > 
> >
> >  Send instant messages to your online friends
> http://uk.messenger.yahoo.com
> >
>




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