engine and drivetrain Original sway bars. Do they "wear out" do to metal

[ScottNC]

While pondering the brilliant simple mechanics of how a sway bar works, I was wondering if over time they weaken, or lose their ability to lessen sway while cornering, as they age. When you think about it, a 30-35 year old sway bar has been twisting back and forth a lot.

Any engineers educated in metal fatigue want to chime in?

.

[rocket_rob]

Likely not. True, the metal is constantly being flexed and stressed (under torsion and compression), but I imagine it's within the normal limits of the metal. There is such thing as "infinite life", meaning the metal is not stressed to the point of permanent deformation.

As for fatigue, do a quick inspectio. Look for hairline fractures around welds or bolt holes. I might think twice if you see anything.

I have not done the computations, this is just instinct of a Mechanical Engr.

[TobyB]

unlike springs that sag, the anti- sway bars are good forever.

Or until they rust through...

t

[mikem]

(nt)

[jerry]

Any engineers educated in metal fatigue want to chime in?

.

well, since you asked...

as stated in an earlier reply, steel does not have a fatigue endurance limit such as aluminum has. in other words, as long as the applied stress due to bending (while cornering) is below the fatigue limit you should have unlimited cycles. if you reach the fatigue limit you would have a finite number of cycles before a crack would initiate.

several factors influence fatigue curves, such as surface condition and heat treat/hardness. temperature is assumed to be relatively stable.

fatigue curves are generated for a particular alloy by testing samples (rotating bend specimens or tensile specimens) at several cyclic stress levels and counting the cycles to failure. intuitively, as the stress level increases the cycle count decreases. however, for steels, there is a stress level below which fatigue failure is unlikely to occur.

however, if you have corrosion pitting or any other stress concentration, such as metal scoring due to abrasion, then you effectively increase the effective stress at those locations. this is what i have observed on the left-hand side engine mounts which are prone to cracking. the bracket is made of stamped steel with a very sharp edge. both my examples showed fatigue cracks emanating from the sharp corner created during the stamping process. an easy fix to have reduced (maybe not eliminate) the tendency to crack would have been to deburr it.

i'll stop now, i couldn't help myself.

[jimk]

Well put Jerry,

Me, I'm a power and thermal guy, my text books and memory have both rotted on the topic.