All properties similar apart from Modulus - Why?

[Angus101]

Hi there,

I'm currently running tensile tests between two pieces of 1050 Aluminum in non-hardened (80MPa) states. One piece has failed in service, the other has not.

I am measuring UT, Yield, Elongation and Youngs Modulus.

The UT and yields are similar between both, but the elongation is higher and the modului are lower in the failed piece.

Ignoring test set-up, and in-service reasons of failure, any ideas why this difference?

Thanks,

A101

 

[MikeHalloran]

Different modulus suggests different alloy.


Mike Halloran
Pembroke Pines, FL, USA

 

[EdStainless]

Either a very different alloy (maybe not even Al?) or a significant difference in the testing and the other results are unreliable.
Every Al alloy that I could look up has a modulus between 10 and 11 million psi.
Have you looked at micros? Any preferential grain orientation?

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[metengr]

Verify your alloy chemical compositions.

 

[TVP]

Angus,

How much difference is there between the two samples? Elongation values that are within several percentage points is to be expected. Modulus is notoriously difficult to measure, and will certainly vary by several tenths, meaning 10.1 vs 10.5 million psi, even with the same alloy, processing, sample size, etc.

 

[Angus101]

Hi, and thanks for all your help so far.

Elongation for the 'good' piece I'm getting 31%, 36% and 22%.
Modulus for the 'good' piece I'm getting 44.1GPa 45.48GPa and 57.2 GPa respectively. (Sorry I don't do Imperial!)

For the 'failed' piece I'm getting 42% 37% and 35%.
Modulus, 70.4Gpa, 42.2Gpa and 40.8Gpa.

I think the 70.4 is a bit of an anomalie, but the rest does suggest it's straining more than the 'good' piece.

Chemical composition is very similar using EDX.

 

[EdStainless]

The modulus of Al is ~70GPa
The low numbers indicate to me that you have inaccurate testing.

Or the material my be yielding at very low strains. Either way the data is not telling you much. You need to look very carefully at the curves and determine what range in being used for the calculations.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[TVP]

I concur with EdStainless. Modulus testing requires everything (grips, frame, load cell, extensometer) to be calibrated to a finer level of detail than what is required for regular tensile testing (yield, tensile, elongation). Regarding elongation, what type of extensometer is being used? Is this test being run using some type of software, such that uniform elongation is separated from total elongation? Together with the shape of the curve this seems like it would be helpful in diagnosing the issue.