[s-cars] Woah! pics link

[Paul Gailus]

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. 

Paul

-----Original Message-----
>From: Mark Strangways <StrangConst at rogers.com>
>Sent: Jul 17, 2007 10:26 PM
>To: LL - NY <larrycleung at gmail.com>, bill mahoney <airbil at gmail.com>
>Cc: Audi S Car List <s-car-list at audifans.com>
>Subject: Re: [s-cars] Woah! pics link
>
>Well being floating 4 piston calipers I would hope that the hydraulics would 
>balance the stresses involved in following a warped rotor.
>It is a poor design that is for sure, I can see where the stress riser might 
>be to cause this failure.
>
>I am happy I went with the bira design for my upgrades as the don't seem to 
>have the same stress problems
>
>My 2 cents anyways
>
>Mark
>----- Original Message ----- 
>From: "LL - NY" <larrycleung at gmail.com>
>To: "bill mahoney" <airbil at gmail.com>
>Cc: "Audi S Car List" <s-car-list at audifans.com>
>Sent: Tuesday, July 17, 2007 9:49 PM
>Subject: Re: [s-cars] Woah! pics link
>
>
>> From what I recall from my engineering days, that kind of
>> failure is caused by bending moments (i.e. torque cause
>> by the caliper following disk flexure). This is truely an
>> alarming form of failure, as this is pretty typical types of
>> loads on a carrier. Glad I'm dispensing with my ECS
>> alloy brakets and going to the steel replacements.
>>
>> LL - NY
>>
>> On 7/16/07, bill mahoney <airbil at gmail.com> wrote:
>>>
>>> http://forums.audiworld.com/s4s6/msgs/180531.phtml
>>>
>>> Verge of catostophic failure I'd say.
>>> Not good.  Not good at all.
>>> Bill~little woah~M
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