[s-cars] Woah! pics link

Thu Jul 19 13:40:41 EDT 2007

Hey guys, 
So I am a Materials Engineer, although I work as a Mechanical Engineer.  I
have some training in this, not tons, but some,  Anyway here is my
evaluation for what it is worth.
Although I have not seen these brackets in person, it does look like SCC
with intergranular Corrosion  the salted roads I would assume are a big
player.  If anyone is interested I have some articles on it.  I see three
issues one is that the brackets are not properly protected against
corrosion, hard anodizing would definitely improve this.  Second is material
selection, 7xxx series is strong but isn't great for scc.  Even more the
added strength is no benefit to these brackets this is because many of the
7xxx have a serious loss of strength at temperature.  Third the orientation
of the grain when machining appears to be in line with the mounting bolts to
the brake caliper, change this so that it's perpendicular and your should
also see a benefit.  To me it seems that the stress is not from the caliper
under braking but more from the constant stress of the bolts being
tightened.  So changing the orientation of the grain should help move it in
a more preferred orientation relative to the predominant orientation of the
stress from the bolts.  I have done some FEA as well as seen others who have
done FEA on these brackets.  The brackets are built so that the stress is
well below what should result in any fatigue failure.  I think this is live
and learn, 1) change the anodizing to Sulfuric from Chromic acid, 2) change
the orientation of the material when machining 3) go to a different alloy, I
would suggest 6061 just as a first pass.

Here are some articles that I think are pertinent, at least what I could
find free on the net.

http://www.key-to-nonferrous.com/default.aspx?ID=CheckArticle&NM=17

http://books.google.com/books?id=lwLer72nHR0C&pg=PA171&lpg=PA171&dq=high+tem
perature+stress+corrosion+cracking+aluminum&source=web&ots=7nZ81sojqw&sig=D7
1rWAzzACq6zXnvUkbi38AJAnc#PPP1,M1

http://images.google.com/imgres?imgurl=http://tc.engr.wisc.edu/UER/uer99/aut
hor1/fig7.jpg&imgrefurl=http://tc.engr.wisc.edu/UER/uer99/author1/content.ht
ml&h=293&w=472&sz=51&hl=en&start=3&um=1&tbnid=6qOUE-frOcSjnM:&tbnh=80&tbnw=1
29&prev=/images%3Fq%3Dstress%2Bcorrosion%2Bcracking%2B7075%26ndsp%3D18%26svn
um%3D10%26um%3D1%26hl%3Den%26safe%3Doff%26rlz%3D1T4GGLJ_enUS227US227%26sa%3D
N

http://ntrs.larc.nasa.gov/search.jsp?R=673636&id=6&qs=Ntt%3D2024%252B6061%25
2B7075%26Ntk%3Dall%26Ntx%3Dmode%2520matchall%26N%3D0%26Ns%3DHarvestDate%257c
1

http://images.google.com/imgres?imgurl=http://corrosion.ksc.nasa.gov/images/
small/scc2_small.jpg&imgrefurl=http://corrosion.ksc.nasa.gov/stresscor.htm&h
=285&w=200&sz=7&hl=en&start=6&um=1&tbnid=OucqfEojkdvIYM:&tbnh=115&tbnw=81&pr
ev=/images%3Fq%3Dscc%2Baluminum%26svnum%3D10%26um%3D1%26hl%3Den%26safe%3Doff
%26rlz%3D1T4GGLJ_enUS227US227%26sa%3DN

http://tc.engr.wisc.edu/UER/uer99/author1/fig7.jpg
This is carbon steel, but it's a good picture of intergranular stress
corrosion.

-----Original Message-----
From: s-car-list-bounces at audifans.com
[mailto:s-car-list-bounces at audifans.com] On Behalf Of Eric Phillips
Sent: Wednesday, July 18, 2007 4:54 PM
To: Taka Mizutani
Cc: s-car-list at audifans.com
Subject: Re: [s-cars] Woah! pics link

I appreciate your "advice", and LOL at the incredible irony of your post.

Don't worry, the subject isn't going away, and neither am I.

On 7/18/07, Taka Mizutani <t44tqtro at gmail.com> wrote:
> Eric-
> You have a big chip on your shoulder about this subject.
>
> You need to CHILL.
>
> If you have a problem with Greg Amy, don't take it out on me. The whole
> ECS/BIRA/RS2 debate that occurred several months ago here, on the BIRA
list
> and on Audiworld was a debacle, if you ask me. Lots of name calling, lots
of
> assumptions, no clear answers.
>
> YOUR ENGINEERING ISSUES BROUGHT UP THEN AND NOW ARE VALID, SO STOP
DEFENDING
> YOURSELF WHEN THERE IS NOTHING TO DEFEND AGAINST.
>
> Technically, none of these brake setups are DOT approved. Audi never
offered
> this brake system on a S4 or S6. The closest thing to DOT approved would
be
> the Movit kit, which is TUV approved and tested, aluminum brackets and
all.
>
> Furthermore, you're running the calipers out of spec by running a 30mm
> rotor. They're designed to use a 32mm thick rotor and 30mm is, IIRC, the
> maximum wear spec on a 993tt rotor (332x32mm designed for use w/ these
> calipers).
>
> Taka
>
>
>
> On 7/18/07, Eric Phillips <gcmschemist at gmail.com> wrote:
> > Mark,
> >
> > Like I said, I don't know if his words are merely careless, or
> > deliberately provocative.
> >
> > And I absolutely disagree with your implied equating of the
> > engineering contained within the various set-ups.
> >
> > The RS2 stuff was designed for legal, road-going cars.  The way we
> > apply it is not DOT-approved, that's true.  But I'd bet on the
> > engineering staff at Porsche/Audi on any day.  I'm guessing most
> > everyone would, given the choices.  And the stakes are higher than
> > money, IMO.
> >
> > The fact that Greg decided to nuke me off the BIRA list rather than
> > produce some sort of data as to the engineering speaks large volumes
> > to me.  After all, if the questions are uncomfortable, it must be the
> > *questioner* that is the problem, right?  I will continue to question,
> > until data is forthcoming.
> >
> > I agree with the inspection aspect, but have always taken it to mean
> > inspection of parts even when they are OEM from the factory.
> >
> > On 7/18/07, Mark Strangways <StrangConst at rogers.com> wrote:
> > > Not to put words into Taka's mouth, but...
> > >
> > > I think you may be reading well into what he was saying.
> > > No where do I hear him saying (or read) that bira brackets are fine.
> > > Mine are... if that interests you !!!
> > >
> > > Perhaps we should all remember that these "upgrades" are NOT for
highway
> use
> > > anyways.
> > > Debating whether or not Audi / Porsche are better made or not is
rather
> mute
> > > in my opinion.
> > > THEY are legal for use on the road, others are not. Pretty cut and dry
> in my
> > > world.
> > >
> > > I choose to use BIRA, others have chosen to use ECS or Stoptech.
Others
> use
> > > the RS2 brackets.
> > > Like you say "Only detailed engineering analysis or test-to-failure
can
> > > answer that question."
> > > And it aint ever gonna be answered. This question has gone on and on
> before
> > > on this list and the bira site.
> > > I think I still remember how that ended.
> > >
> > > If you want safety, stick with the factory stuff. It works, not great,
> but
> > > it works and is the only thing that will save you from being denied an
> > > insurance claim. Otherwise, use what you want and cover your ass with
> > > inspections as should be done with all safety associated parts on an
> > > automobile.
> > >
> > > Just MHO, and no one should read anything into that.
> > >
> > > Mark
> > >
> > > ----- Original Message -----
> > > From: "Eric Phillips" < gcmschemist at gmail.com>
> > > To: <s-car-list at audifans.com>
> > > Sent: Wednesday, July 18, 2007 4:07 PM
> > > Subject: Re: [s-cars] Woah! pics link
> > >
> > >
> > > > Taka:
> > > >
> > > > Debacle?!?  Reasoned arguments sprinkled with educated speculation
are
> > > > not the stuff of "debacles".
> > > >
> > > > You are correct that there have been no *reported* cracking issues
> > > > with BIRA brackets.  Lack of reportage does not imply that the
design
> > > > is adequate.  Only detailed engineering analysis or test-to-failure
> > > > can answer that question.
> > > >
> > > > I'm not sure if you're being provacative or careless in your word
> > > > choices.  If you have data to put the questions to rest, I'd love to
> > > > see them.  I will gladly eat a huge helping of cold crow if the data
> > > > turn out to refute my position in the matter.  My only concern, from
> > > > the very beginning, is the safe transport of my fellow UrS car
> > > > drivers.  If the BIRA stuff can do that equally as well as the
> > > > Porsche/Audi-designed stuff, cool.  If not, then folks looking to
> > > > upgrade shouldn't be steered in that direction.
> > > >
> > > > It's really just that simple, IMO.
> > > >
> > > > Which is exactly why I chose RS2 brackets and A8L D2 rotors for my
> > > > BBK.  Cheap, effective, proven.  ECS?  Avoid.  BIRA?
> Unknown,
> > > > excessive legalese, slow to get parts, and more expensive.
> > > >
> > > > From where I sit, it looks like a pretty clear choice.  But as in
all
> > > > matters of human endeavor...
> > > >
> > > > Eric
> > > >
> > > >> Date: Wed, 18 Jul 2007 10:44:16 -0400
> > > >> From: "Taka Mizutani" < t44tqtro at gmail.com>
> > > >> Subject: Re: [s-cars] Woah! pics link
> > > >>
> > > >> I do recall something about the improvements that ECS made to their
> > > >> brackets
> > > >> after the whole cracking thing came to light several months ago.
> > > >>
> > > >> I do know that ECS will replace existing brackets at no cost to the
> > > >> customer, other than shipping, IIRC.
> > > >>
> > > >> After the whole ECS debacle, there was another debacle about BIRA
and
> > > >> debate
> > > >> whether or not BIRA's brackets may do the same thing, but I don't
> think
> > > >> any
> > > >> cracking reports have occurred with the BIRA brackets.
> > > >>
> > > >> I thought the ECS brackets placed the caliper in the same
orientation
> as
> > > >> the
> > > >> RS2 brackets. If that's not the case, then using RS2 brackets would
> > > >> necessitate a custom hat or the use of A8L one-piece rotors. At
least
> the
> > > >> RS2 brackets are forged steel, so the chance of stress cracking is
> much
> > > >> lower.
> > > >>
> > > >> Taka
> > > >>
> > > >>
> > > >> On 7/18/07, Paul Gailus < gailus at mindspring.com> wrote:
> > > >> >
> > > >> > While I'm not a metallurgist, I have a suspicion that this
failure
> > > >> > could've been caused by stress corrosion cracking and/or fatigue
> > > >> > cracking
> > > >> > along the grain of the aluminum alloy. Hot-rolled plate stock
will
> tend
> > > >> > to have some unrecrystallized grain structure in layers that can
> act as
> > > >> > slip planes in a fracture.
> > > >> > For example, see the discussion at:
> > > >> > http://www.key-to-metals.com/Article114.htm
> > > >> >
> > > >> > Being in the "salt belt" probably didn't help either, Bill ;-)
> > > >> >
> > > >> > Some suggested alternatives in the design would be:
> > > >> > 1. use an alloy more resistant to stress corrosion cracking, and
> > > >> > include
> > > >> > ferrous alloys in the selection process
> > > >> > 2. counterbore for a steel nut so that the aluminum bracket
doesn't
> > > >> > have
> > > >> > to be threaded and therefore be more susceptible to
> stress/corrosion.
> > > >> > 3. the existing counterbores for bolts to the strut housing could
> > > >> > have a larger radius applied with a ball mill to minimize stress
> > > >> > raisers.
> > > >> >
> > > >> > Perhaps the redesigned brackets have some improvements in these
or
> > > >> > other
> > > >> > areas.
> > > > _______________________________________________
> > > > S-CAR-List mailing list
> > > > S-CAR-List at audifans.com
> > > > http://www.audifans.com/mailman/listinfo/s-car-list
> > > >
> > >
> > >
> >
> >
> > --
> > Eric
> >
> > 1995 UrS6 "Silber Geist"
> > _______________________________________________
> > S-CAR-List mailing list
> > S-CAR-List at audifans.com
> > http://www.audifans.com/mailman/listinfo/s-car-list
> >
>
>

-- 
Eric

1995 UrS6 "Silber Geist"
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