Subject: RE: Tubular contro arms, any interest??

[Larry C. Leung]

As I recall, the technique for infinite life on steel parts essentially
(without
going into all of the details) meant adding more material. As aluminum is
essentially 1/3 the mass, but 1/3 the strength of steel, the big
advantage
being that you could make it's shape such that you could recover most
of the needed strength without adding all of the mass back. So, I wonder
how they get longer service life out of aluminum? Adding more mass would
defeat the purpose entirely, and as I recall, with aluminum, adding mass 
wouldn't help, it was a # of cycles issue that causes aluminum to fail
by stress cracking, no matter how big the part. I'd imagine you could
get a bit more life by designing stiffer (less bending, therefore less
potential
for cracking) parts (usually by larger cross section, not necessarily by 
added mass), but ultimately, unless they've developed material changes to
the aluminum itself, the cycles issue is going to come up. 

Finally, Taka put this better than I could've. The cost of recovering the
overly complex electronics of the newer (even steel-based) luxo cars
is likely to be prohibitive, and dealer only. Although the A/S8 are
stunning
cars (got passed by a new A8L today, WOW does it look extremely 
serious in the mirrors, and nobody got in it's way. The HID's helped) 
cars, I'd doubt I'd ever consider one for precisely for that reason. 

LL - NY


On Fri, 13 Feb 2004 11:08:44 -0500 JShadzi at aol.com writes:
> Considering that a large majority of cars manufactured these days use 
> cast alum suspension parts, I'm sure they've developed the parts to 
> a level where fatigue of the material is well outside the extreme 
> useage life of the parts.
> 
> Javad
> 
> >
> >Unless there are any seams where ionic (salt laden)
> >moisture can accumulate and stay active for a LONG
> >time, I don't think that corrosion would be an issue,
> >although it's certainly MUCH more of a concern in a 
> >car compared to an airplane (they usually don't salt
> >the skies! except for cloud seeding, which is pretty
> >much not happening anymore). It'll be interesting to
> >see if 3rd or 4th owners will occur for these cars, 
> >they're so complex and costly to repair bodywork that
> >they'd most likely be junked (or at least in Europe,
> >recycled) rather than passed on to new owners. I'd 
> >think the cost of refurbing an A8 would be prohibitive
> >to most of us on the list, whom consider things like
> >type 44 TQ's an easy ticket to performance....
> >
> >LL - NY
> >
> >
> >>And whom is ever checking
> >>an A8's shock 
> >>towers or rocker areas for cracking, as they do with aircraft?
> >>
> >>  
> >>
> >I think the problem with failing aluminum parts is not one for the 
> first 
> >2 owners to worry about.  I am sure (or rather hope) that they 
> designed 
> >the parts so the fatigue life, even if not infinite, is very long. 
>  So 
> >maybe the guy in 2045 who can still afford to find and put gas 
> through 
> >his A8 for Sunday cruises should be checking things.  However now 
> that I 
> >say that the primary driver would be mileage not age.  Although 
> with 
> >aluminum corrosion might play a part.  Does Audi anodize the A8 
> chasis?
> >
> >-- 
> >Eric Sanborn
> >'85 4ktq
> >
> >http://sofadog.net/4ktq/
> >
> >
> >
> 
>