[s-cars] Woah! pics link

[Matt twentyV]

interesting info.  But my car is in coastal CA and has
never seen salt.  So corrosion might be a contributor
but is not required for this failure mode.
-Matt
--- Trevor Frank <frankracing at gmail.com> wrote:

> 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.
> 
=== message truncated ===



       
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