[Rhodes22-list] Short Cycle Fatigue Failure In StainlessSteel Tang

Fri May 7 00:03:15 EDT 2004

Peter,

The line could be used instead of the SS shackle between the eyebolt & the
upper block on the mainsheet tackle.  The line would be lighter than a SS
shackle ; but, would be subject to UV degradation & chafe wear.  If it were
regularly inspected & periodically replaced, the line would be an acceptable
substitute for the shackle.

Roger Pihlaja
S/V Dynamic Equilibrium

----- Original Message -----
From: "Peter Thorn" <pthorn at nc.rr.com>
To: "The Rhodes 22 mail list" <rhodes22-list at rhodes22.org>
Sent: Thursday, May 06, 2004 9:27 PM
Subject: Re: [Rhodes22-list] Short Cycle Fatigue Failure In StainlessSteel
Tang

> Slim and Roger,
>
> Alternatively, you could use a piece of light weight high-strength modern
> sailing line -- to add a little separation so the boom end block doesn't
> chafe on the boom end.  3/16" Vectran would be good for 4,750 pounds load
> http://layline.com/llf/llpages/htmlp2origa/page2.htm     Think that would
do
> it?
> Harken now recommends attaching some of its blocks with line for strength,
> flexibility and weight savings.
>
> PT
>
>
>
>
> > Slim,
> >
> > How about replacing the bolt & tang with a threaded SS eyebolt into the
> end
> > of the boom & a shackle to the mainsheet?
> >
> > Roger Pihlaja
> > S/V Dynamic Equilibrium
> >
> > ----- Original Message -----
> > From: "Steve Alm" <salm at mn.rr.com>
> > To: "Rhodes" <rhodes22-list at rhodes22.org>
> > Sent: Thursday, May 06, 2004 3:28 PM
> > Subject: Re: [Rhodes22-list] Short Cycle Fatigue Failure In
StainlessSteel
> > Tang
> >
> >
> > > Roger,
> > >
> > > As always, very complete remarks.  The bolt is not tight and the tang
> > > rotates freely.  But when lowered, the end of the boom is about 18"
from
> > the
> > > traveler and just slightly higher.  The tang normally points down with
a
> > > slight angle aft.  When sheeted in tightly, the force is leveraged
> against
> > > the bolt alone and is easily bent until it's pointing at the traveler.
> It
> > > didn't take much effort to bend it back either.  According to your
info,
> > > this suggests a substantial amount of damage to the crystal structure.
> > It's
> > > hard to imagine all the disastrous possibilities if it were to
> break--like
> > > you say--just when I need it the most.  So it must be replaced.  I
can't
> > > help but think there's a better piece of hardware for this than a
rigid
> > > tang.  Maybe just a padeye on the end of the bolt?
> > >
> > > Thanks for your help,
> > > Slim
> > >
> > > On 5/6/04 7:22 AM, "Roger Pihlaja" <cen09402 at centurytel.net> wrote:
> > >
> > > > Slim,
> > > >
> > > > How tight do you keep the bolt that secures the tang to the end of
the
> > boom?
> > > > The bolt is supposed to be sufficiently loose that the tang can
rotate
> > > > smoothly about the bolt.  As long as the tang can rotate to keep the
> > loads
> > > > aligned down the C.L. axis; then, it should never bend.
> > > >
> > > > Assuming your tang is a piece of electropolished stainless steel
like
> on
> > > > Dynamic Equilibrium, the fact that you did bend it is a cause for
> > concern.
> > > > The nickel/chromium stainless steel alloys like 304 SS and 316 SS
have
> a
> > > > nasty propensity to strain harden.  That means that once the piece
has
> > been
> > > > loaded enough to cause permanent deformation (i.e. a permanent
bend);
> > then,
> > > > the crystal structure of the metal has been damaged.  When you bent
it
> > back
> > > > straight, you further increased the amount of damage.  The only
> solution
> > > > would be to heat the metal above the so-called "recrystallization
> > > > temperature", for about an hour.  Assuming the bend was not too
> severe,
> > the
> > > > recrystallization temperature for a 300 series stainless steel alloy
> is
> > > > about 450 deg C.  This time/temperature treatment will permit the
> > metal's
> > > > crystal structure to "heal" itself.  If you either don't want to do
> that
> > or
> > > > don't have access to a furnace; then, you might consider replacing
the
> > tang.
> > > > The damage to the crystal structure also causes the metal to become
> > > > embrittled.  Brittle failure is a cumulative damage sort of
phenomena.
> > > > Brittle microcracks may have been initiated by bending the tang and
> then
> > > > bending it back.  Now, normal sailing loads will cause the
microcracks
> > to
> > > > coalesce into macrocracks and cause the cracks to grow until the
tang
> > can no
> > > > longer handle the load.  The presence of salt crystals in the air or
> the
> > > > water that splashes on the tang will accelerate this phenomena.  The
> > final
> > > > failure will occur in a spectacular brittle manner when the tang is
> > heavily
> > > > loaded.  i.e. The tang will fail with loud "kerpow" just at the
moment
> > when
> > > > you needed it most!
> > > >
> > > > The whole phenomena I've described above is called "short cycle
> fatigue
> > > > failure" (SCFF) & we studied it as well as how to design
pieces/parts
> to
> > > > prevent it in my ME451, Machine Design class, last semester.  SCFF
is
> > > > usually an insidious hidden problem.  The tang will probably look
just
> > fine
> > > > right up to the moment it fails catastrophically under load.  SCFF
is
> > also
> > > > best described in terms of statistics, rather than in absolute
terms.
> > In
> > > > other words, how "perfect" was the tang's crystal structure to begin
> > with,
> > > > did the bend just happen to load up some of these built-in crystal
> > structure
> > > > defects & initiate microcracks, and now how often will normal
sailing
> > place
> > > > loads on the tang that will cause these microcracks to grow?  All
> three
> > of
> > > > these questions can best be answered in terms of statistical
> > probabilities &
> > > > the final SCFF will be some complex function of all three factors.
> The
> > > > final question is, "How serious would it be if the tang failed under
> > load at
> > > > a critical moment?"  Only you can answer that question.
> > > >
> > > > If it were my boat; then, I would either heat treat the tang or
> replace
> > it.
> > > >
> > > > Good luck!
> > > >
> > > > Roger Pihlaja
> > > > S/V Dynamic Equilibrium
> > > >
> > > > ----- Original Message -----
> > > > From: "anima13" <anima13 at bellsouth.net>
> > > > To: "The Rhodes 22 mail list" <rhodes22-list at rhodes22.org>
> > > > Sent: Wednesday, May 05, 2004 9:00 PM
> > > > Subject: RE: [Rhodes22-list] First Reef Question
> > > >
> > > >
> > > >> Slim,
> > > >> I did that the first year single handing and never bent it back!
> > > >> Has been fine and going into 5th year.
> > > >> Anne
> > > >>
> > > >> -----Original Message-----
> > > >> From: rhodes22-list-bounces at rhodes22.org
> > > >> [mailto:rhodes22-list-bounces at rhodes22.org]On Behalf Of Steve Alm
> > > >> Sent: Wednesday, May 05, 2004 12:19 PM
> > > >> To: Rhodes
> > > >> Subject: [Rhodes22-list] First Reef Question
> > > >>
> > > >>
> > > >> I had a wonderful sail yesterday.  Temps in the mid-sixties, sunny
> and
> > > > winds
> > > >> 13 gusting to 21.  I was single-handing and had lots of fun washing
> the
> > > >> rails.  Rummy woulda been proud.  8-)  I had the boom in the lower
> > > > position
> > > >> (first reef) which is something I rarely do.  I suppose I should do
> it
> > > > more
> > > >> often when winds get that high--I guess I just prefer the headroom.
> > > > Anyway,
> > > >> with the boom down and when close-hauled, I noticed I had bent the
> tang
> > > > (?)
> > > >> ...the ~4" piece of steel at the end of the boom where the main
sheet
> > > >> attaches.  When the boom is down and sheeted in tightly, the tang
> bent
> > > > back
> > > >> towards the traveler.  When I was done sailing, I bent it back to
its
> > > >> original shape.  Obviously, I don't want to keep doing this because
> > > >> eventually it'll break.  Has anyone had this problem or found a
> > solution?
> > > >>
> > > >> Slim
> > > >>
> > > >> __________________________________________________
> > > >> Use Rhodes22-list at rhodes22.org, Help? www.rhodes22.org/list
> > > >>
> > > >> __________________________________________________
> > > >> Use Rhodes22-list at rhodes22.org, Help? www.rhodes22.org/list
> > > >>
> > > >
> > > >
> > > > __________________________________________________
> > > > Use Rhodes22-list at rhodes22.org, Help? www.rhodes22.org/list
> > >
> > > __________________________________________________
> > > Use Rhodes22-list at rhodes22.org, Help? www.rhodes22.org/list
> > >
> > >
> >
> >
> > __________________________________________________
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>
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