steel with low modulus of elasticity

[Tmoose]

There are stories here of a crusher shaft that(1) bent in service or (2) had a low natural frequency. The steel reportedly test OK chemically, but demonstrated low modulus during some physical tests.

I'm trying to find out more, but in my mind I'm clutching to the Bauschinger effect as a >>possible<< explanation. Is it possible if the test sample was cut from a peculiarly yielded piece of the shaft an odd, low modulus might be measured?

Thanks,

Dan T

 

[redpicker]

I don't think the Bauschinger effect would change the elastic modulus. In my experience, the most common reason for a low "observed" modulus during a tensile test would be bending of the tensile specimen during the test (ie, not completely axial loading).

rp

 

[davidmoul]

Try another way to test it (Ultrasonic testing) to check your results. Must be a problem of manipulation.

Are you sure that there is no heat treatment responsible for this low modulus?

 

[btrueblood]

Cast iron has a significantly lower modulus than steel, could the part have been cast? Should be easy to tell from %carbon chemical analysis.

 

[Tmoose]

Only emotion charged hear-say evidence available so far.
Supposedly Russian made alloy steel ~ 1045 2 or 3 years ago. Maybe hot rolled, where historically we used forgings.
What makes me stumble is a >>report<< that the machine demonstrated a critical speed ~ 30% lower than is typical, and that a new shaft "fixed" it. Critical speed would be a Young's modulus thing, not a yield strength related phenomenon, so i'm used to thinking any old steel would act the same.

I doubt the material exists for re-test.

http://www.civil.canterbury.ac.nz/ruaumoko/Gif/Loops/Loop39.GIF

http://www.brushwellman.com/alloy/tech_lit/oct99.pdf

The charts explain many reports and first hand experience that un-bending a shaft over-corrected during straightening is "easier" or lower effort.

 

[arunmrao]

Normally crusher shafts are made in EN 24 steel,suitably hardened and tempered to have toughness.

If the shaft has bent,it indicates that it is in a soft state. Did some kind of a bearing seizure or mechanical obstruction restrict the shaft motion,thereby increasing the temperature causing it to soften.It is only a wild conjecture.

Chocolates,men,coffee: are somethings liked better rich!!
(noticed in a coffee shop)

 

[redpicker]

What makes me stumble is a >>report<< that the machine demonstrated a critical speed ~ 30% lower than is typical, and that a new shaft "fixed" it. Critical speed would be a Young's modulus thing, not a yield strength related phenomenon, so i'm used to thinking any old steel would act the same.

Just a WAG here, but might straightness also affect critical speed? The Baushinger effect _will_ affect the ability to straighten a shaft. What I'm thinking is that if the shaft had been yielded in compression and straightened, it might not hold that straightness over normal service loads, affecting the critical speed. Just a WAG. Other than that, I've got nothing.

rp