900+K mile 300 SDL?

[LoosBenz]

Ok, apparently it needs another (4th) engine, but 300+K per engine on average isn't TOO bad. Too far for me to buy, but I'm tempted to contact the seller to find out what failed.

http://cgi.ebay.com/ebaymotors/Mercedes-Complete-Car-without-Diesel-Engine-300-SDL-87-_W0QQcmdZViewItemQQhashZitem35b23b0210QQitemZ230623478288QQptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccesso ries

[Skippy]

The Buy it Now price seems a tad high, but not ridiculous. Then you have the matter of being able to brag about how many miles your car has on it. I thought I was doing pretty good with 312,000 miles.

[layback40]

Some one should offer him $1.00 !
With those sort of miles its ready to fall to pieces. There would be fatigue every place you looked.

[snookwhaler]

Originally Posted by layback40

Some one should offer him $1.00 !
With those sort of miles its ready to fall to pieces. There would be fatigue every place you looked.

Yea....

But, it's all "Highway Miles"!!

[Skippy]

Meh, ferric alloys don't fail in cyclic loading as long as you keep the magnitude under about 60% of the yield stress. Aluminum is not so, which is why airframes always eventually have to be retired. A steel car body can go pretty much forever as long as you protect it from corrosion.

[layback40]

Originally Posted by Skippy

Meh, ferric alloys don't fail in cyclic loading as long as you keep the magnitude under about 60% of the yield stress. Aluminum is not so, which is why airframes always eventually have to be retired. A steel car body can go pretty much forever as long as you protect it from corrosion.

Best I refer you to a good mechanical engineering text like "Design of Machine Elements, V.M. Faires". Small cyclic loads on most steel does cause fatigue failure eventually especially in normal atmospheric conditions.

[Crazy_Nate]

Originally Posted by layback40

Best I refer you to a good mechanical engineering text like "Design of Machine Elements, V.M. Faires". Small cyclic loads on most steel does cause fatigue failure eventually especially in normal atmospheric conditions.

I think you're arguing about the same thing

Corrosion does play a rather large role in fatigue (especially because it likes to form at highly stressed areas and make them worse). Most steels are susceptible to corrosion in normal atmospheric conditions, so...unless you keep things in very good shape...

I'd say that's a tired car

[LoosBenz]

http://www.volvocars.com/intl/top/about/news-events/pages/default.aspx?itemid=192

Surely a Mercedes can do AT LEAST as well as a Volvo, right?

[Skippy]

After some checking, the value is 50% of the ultimate tensile strength, not 60% of the yield strength as I previously stated. I do concede that corrosion can contribute to fatigue failure at lower stress levels.

From Machine Design: An Integrated Approach 2nd Edition Robert Norton, page 332:

ENDURANCE LIMIT Note that the fatigue strength S falls steadily and linearly (on log-log coordinates) as a function of N until reaching a knee at about 10^6 to 10^7 cycles. This knee defines an endurance limit Se(primed) for the material, which is a stress level below which it can be cycled infinitely without failure. At the lower bound of the scatter band beyond the knee, an approximate endurance limit can be defined.

for steels: Se(primed) (approximately equals sign) 0.5Sut Sut<200ksi

There follow a few notes that not all steels exhibit this, but most do, and that aluminum and some other alloys do not. There is also mention that endurance limits for steels with higher UTS don't generally exceet 100 kpsi.

In another chapter it mentions that if a car or truck body fails, it normally does so in low cycle fatigue coming from the infrequent large loadings on the material, rather than the very frequent small loadings.

This is why I've never seen a fatigue failure in a body component on any vehicle, regardless of mileage, that stayed on pavement its entire life, and why I've seen tons of these failures on things that are off-roaded hard.

Thanks for making me get one of my old college textbooks out. I appreciate the mental exercise

[sky44]

Originally Posted by Skippy

Meh, ferric alloys don't fail in cyclic loading as long as you keep the magnitude under about 60% of the yield stress. Aluminum is not so, which is why airframes always eventually have to be retired. A steel car body can go pretty much forever as long as you protect it from corrosion.

maybe the steel is still ok, but any moving parts in the car are about done, as well as anything made of rubber.
the corrosion protection is a big IF.

might be worth 100 bucks for the parts if you got a place to keep it...