steel E variation <30,000,000 psi

[Tmoose]

There is a report here that physical properties testing on a steel shaft (mat'l probably hot rolled 1140 annealed) indicated E=26,000,000 psi.

I understand metal physical properties can not be counted on to be sharply defined numbers, but instead are a range. And, that most tables do not differentiate between transverse and longitudinal properties, which I believe can be significant for endurance and yield strength, but had not heard being significant for E.

Still, a test result ~10% low seems "odd," and unfortunately in this case, important.

Anyone have similar experiences?

thanks,

Dan T

 

[CoryPad]

Yes, I have had similar experience. Elastic moduli are considered invariant, but they aren't. For example, elastic moduli vary with crystallographic orientation, so heavily deformed parts can exhibit variations.

However, the largest variations I have seen are from the test method used. If the elastic modulus was determined by strain measurement, the extensometer accuracy must be scrutinized. The small elastic deflection during a tension test may not be the best way to determine elastic modulus.

If elastic modulus needs to be known with accuracy, try multiple test methods. Shear, tension, bending modes, and longer sample length to increase the elastic deflections.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[redpicker]

If this result comes from a tensile test report, I'm not surpirsed with the result. As CoryPad mentioned, the accuracy of extensometers used for normal tensile testing can introduce a big error in the (apparent) elastic modulus. In addition, the geometry of the specimen is important. ASTM allows a rather generous "taper" in both round and rectangular specimens, so the cross-sectional area of the specimen in the gauge length is not constant. Furthermore, alignment of the ends of the specimen can introduce bending, which adds more error.

rp

 

[EdStainless]

When we needed good modulus numbers in tensile tests we used bars with no draft (taper) and we would load the sample slightly (about 1/3 of the expected yield strength)then unload to a couple hundred pounds of load, and then reload. We would take the modulus from the second load data. This takes the slack out of the test system and gives you better data. We usually didn't even bother breaking these bars.

Under normal test methods coming up with 26 instead of 29 is not unexpected.

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Plymouth Tube

 

[Tmoose]

thanks y'all

Dan T