harryproa : Messages : 2073-2102 of 6719

Rob Denney <proa@...> · 2073 - 2102

-Thanks Mike,
  I didn't realise that carbon had greater stetch before breaking than
glass.
My thought on the creaking and cracking concur with yours that it is
probably the resin not being able to stretch enoughand some breaking
of the fibre resin bond. I also think that the cross fibresresin
attachment needed to keep the compression side from buckling may also
crack. The concern to me is that the cracing on the ww side weakens
the side for subsequent compression when the load changes. The 99.9%
stability is nice to read.
  Robert -- In harryproa@..., Mike Crawford
<jmichael@g...> wrote:
>
>
>   After much research, I agree with both Peter and Rob.
>
>   In summary:  epoxy cracking likely occurs in first tension on the
> leading edge, while structural failure of the mast likely occurs in
> compression on the trailing edge.  The cracking sound will probably
be
> more of an issue for carbon and less of an issue for kiri/glass.
Also,
> it appears that  Rob's cold vacuum process for creating spars is
> superior to the heated autoclave process, and carbon and kevlar
> laminates are better than aluminum in terms of long-term fatigue.
>
>   The rest of this long post contains some of the links and
> explanation.  It's not definitive, but at least it has some real
data.
>
> ---
>
> EPOXY PROPERTIES
>
>   I originally made two faulty assumptions:  a) epoxy stretches
more
> than it actually does, and b) epoxy is isotropic, i.e., it has the
same
> modulus in both compression and tension.  The first assumption
stemmed
> from the fact that the flexible epoxies used in some repair work
are
> different from the stiff epoxies used to create masts.  The second
> assumption came from some research refers to epoxies as being
> quasi-isotropic, which I misinterpreted.
>
>   Thanks to Peter for pointing out that epoxy has different modulii
for
> tension and compression.  Unfortunately it took me over half a day
to
> get actual numbers to verify this.
>
>   As far as stretch goes:
>
>     http://www.tech.plym.ac.uk/sme/MATS324/MATS324A5%20CFI.htm
>
>     Epoxy only elongates to 2% before cracking, while carbon fiber
can
> elongate up to 10% before failure, and E-glass to 3.37%.  As the
leading
> edge of a mast stretches, the epoxy will crack before carbon fibers
or
> E-glass fibers will break.
>
>   As far as modulus goes:
>
>     http://www.rpi.edu/locker/38/001238/pdfs/load.pdf
>
> http://www.google.com/search?
q=cache::www.rpi.edu/locker/38/001238/pdfs/load.pdf
>     (same as above, but html version)
>
>   Epoxy alone has a modulus that is 17% greater in compression than
in
> tension, and an epoxy/carbon composite has a modulus that is 21%
greater
> in compression than in tension.  Both epoxy and epoxy/carbon
composite
> will stretch more under a given force in tension than they will
shrink
> under the same force in compression.
>
> ---
>
> MAST CRACKING
>
> Scenario A: flexible unstayed carbon mast
>
>   If the mast is designed to be flexible, the smaller tension
modulus
> means that the windward side of the mast will stretch more in
tension
> than the leeward side will shrink in compression, and epoxy's
earlier
> failure due to strain means that the stretching is going to crack
the
> epoxy while leaving the carbon fibers intact.  These cracks will
weaken
> the mast, but won't themselves represent a structural failure
because
> the undamaged carbon is still very strong.
>
> Scenario B: stiff unstayed carbon mast
>
>   If the mast is stiff enough to keep the epoxy from elongating
past its
> strain limit, cracks won't occur in tension on that windward edge.
> Instead, cracks will develop from compression in the leeward edge
as the
> matrix starts to buckle.  This is not necessarily better than the
> flexible mast, just different.
>
> Scenario C: kiri/glass mast
>
>   Because of wood's inherent flexibility, and the lower modulus of
> fiberglass when compared to carbon, the cracking is likely in the
epoxy
> on the windward edge.  I don't have a modulus or strain data for
kiri to
> test this.
>
> ---
>
> MAST FAILURE
>
>    When a failure does occur, it will likely happen on the leeward
edge
> under compression.  This is because the fibers under tension
require no
> support, and therefore don't put buckling stress on the matrix,
while
> the fibers under compression will eventually buckle once the epoxy
fails
> to keep them in column.  Worded differently, the compressed side is
> stiffer than the stretched side, but ultimately more susceptible to
failure.
>
> Scenario A: flexible unstayed carbon mast
>
>   This mast will provide warning before failure, with the leading
edge
> cracking before the trailing edge buckles. That's definitely a
plus.
> However, the cracks will weaken the mast over time  The more cracks
> there are in the epoxy matrix, the less it will be able to keep the
> fibers from buckling, and the more likely it will fail in
compression.
> Moral of the story: avoid stresses that cause the cracking sound.
>
> Scenario B: stiff unstayed carbon mast
>
>   For a stiff carbon mast, this means that there won't be the
benefit of
> hearing the micro-cracks in the leading edge as the mast gets
stressed.
> That's a bummer if the mast has not been designed to be strong
enough to
> handle the dynamic loads involved in a huge gust capsizing the
boat.  If
> the mast is strong enough, the issue then becomes making the boat
strong
> enough to handle the stress, while also surviving the knockdown.
Many
> folks would rather have the mast fail.
>
> Scenario C: kiri/glass mast
>
>   Failure will likely be in compression because wood does better in
> tension than compression, and a hollow mast will eventually buckle
in
> compression when subjected to too much force.  Fortunately, the
cracking
> should be less of an issue with the kiri/glass mast.  First, the
kiri
> itself is going to provide more resistance to compression than the
> glass/epoxy skin.  Second, even if the epoxy is cracked, the glass
will
> still hold tension, and will still help prevent the kiri from
buckling.
>
> ---
>
> VACUUM-BAGGING VERSUS AUTOCLAVE
>
>     http://www.gmtcomposites.com/the_autoclave_myth.htm
>
>   Autoclaved prepreg masts are stronger and stiffer in tension and
> compression, while vacuum bagged masts are better in shear.  Six on
one
> side, a half-dozen on the other.  However, vacuum-bagged masts can
be
> made in one long piece, regardless of length.  Autoclaved masts, on
the
> other hand, must be spliced together from sections that fit in the
> autoclave.  For a small mast, this doesn't matter.  For a large
mast,
> this means joints between sections, and that's less desirable than
a
> single piece.
>
> ---
>
> FATIGUE
>
>     http://www.tech.plym.ac.uk/sme/MATS324/MATS324A5%20CFI.htm
>
>   "Under a static load of 50% ultimate stress, the probability of
> survival for carbon/epoxy, Kevlar/epoxy and glass/epoxy over a 30
year
> period are 99.99%, 99.8% and 22% respectively.  Under a load of 40%
> ultimate stress, the survival probability for glass/epoxy is 97%"
>
>     http://www.cstcomposites.com/505_carbon_spar.htm
>
>   "Fatigue resistance orders of magnitude better than
Aluminium  .Life
> Span - pretty well indefinite with normal sailing loads apart from
> normal wear and tear."
>
>   Not that anyone needed a reason to like carbon.  I've just seen
fans
> of aluminum insulting carbon's ability to resist fatigue.  I
suppose
> early designs could have had problems, but that would seem to be a
> design or manufacturing issue, not a materials issue.
>
>        - 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 <mailto:proa@i...>
> >     To: harryproa@...
> >     <mailto:harryproa@...>
> >     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 -----
> >         From: Doug Haines <mailto:doha720@y...>
> >         To: harryproa@...
> >         <mailto:harryproa@...>
> >         Sent: Friday, November 03, 2006 1:13 PM
> >         Subject: Re: [harryproa] Re: masts
> >
> >         Rob,
> >
> >         Is composite glass/kiri?
> >
> >         Doug
> >
> >
> >
> >         Rob Denney <proa@i... <mailto:proa@i...>> 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 -----
> >                 From: Doug Haines <mailto:doha720@y...>
> >                 To: harryproa@...
> >                 <mailto:harryproa@...>
> >                 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@y...
> >                 <mailto:cateran1949@y...>> 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@..., "Robert"
> >                     <cateran1949@y...> wrote:
> >                     >
> >                     > --- In harryproa@..., 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
> >                     <http://uk.messenger.yahoo.com/>
> >                     > >
> >                     > >
> >                     > >
> >                     > >  Send instant messages to your online
friends
> >                     > http://uk.messenger.yahoo.com
> >                     <http://uk.messenger.yahoo.com/>
> >                     > >
> >                     >
> >
> >
> >
> >
> >                 Send instant messages to your online friends
> >                 http://uk.messenger.yahoo.com
> >                 --------------------------------------------------
----------------------
> >                 Internal Virus Database is out-of-date.
> >                 Checked by AVG Free Edition.
> >                 Version: 7.1.385 / Virus Database: 268.11.5/426 -
> >                 Release Date: 8/23/2006
> >
> >
> >         ----------------------------------------------------------
--------------
> >         The all-new Yahoo! Mail
> >
<http://us.rd.yahoo.com/mail/uk/taglines/default/nowyoucan/free_from_i
sp/*http://us.rd.yahoo.com/evt=40565/*http://uk.docs.yahoo.com/nowyouc
an.html>
> >         goes wherever you go - free your email address from your
> >         Internet provider.
> >
> >         ----------------------------------------------------------
--------------
> >         Internal Virus Database is out-of-date.
> >         Checked by AVG Free Edition.
> >         Version: 7.1.385 / Virus Database: 268.11.5/426 - Release
> >         Date: 8/23/2006
> >
> >     --------------------------------------------------------------
----------
> >     No virus found in this incoming message.
> >     Checked by AVG Free Edition.
> >     Version: 7.1.409 / Virus Database: 268.13.17/505 - Release
Date:
> >     2006/10/27
> >
> >
>

Yahoo!7 Groups Tips

Did you know...

Messages

YAHOO!7 SPONSOR RESULTS