Accuracy of Tensile Testing 304SS Micro-Tubes

[tomtom412]

Hi All

I am looking to find out if anyone has any input on whether tensile testing a micro-tube (OD 0.66mm, ID 0.48mm) made from 304ss would be accurate enough to derive material properties e.g. tensile modulus, uts, yield stress etc..
Or is it more appropriate to use larger, solid cross-section test samples?

I ask as the testing I have done, yields very high (>1200 MPa) strengths compared to what I know to be the UTS of 304ss (~550 MPa) and am unsure if theres something simple i am missing?

Any guidance at all would be great as I am very rusty on my materials and could use the help!

Thanks

Regards,
Tom

 

[metengr]

What actual tensile testing have you performed thus far? Were the tensile tests on actual microtube samples held in grips? Where did the tensile failures occur?

Typically, tensile testing is performed to a standard, like ASTM A 370, for proper comparison and determination of mechanical properties. It is possible your higher tensile values are due to processing effects, like cold work, that can result in higher tensile values as a result of work hardening.

 

[tomtom412]

Metengr,

Thanks for the reply. I tensiled some samples, to ASTM A370 annex A2, parts were held by pneumatic grips. The tubes were formed via extrusion, but past that have not seen any more processing. The failure was also as expected.

Regards,
Tom

 

[Compositepro]

Metal properties can depend highly upon how the sample was processed. Drawn wire typically has far higher strength than cast steel. I would expect drawn tubing to be quite a bit stronger than lightly rolled SS.

 

[EdStainless]

IF these were formed cold or warm they will have significant cold work in them and be a lot stronger.
1200 MPa isn't out of the question, but I would expect very low ductility at this strength.
And they should be highly magnetic.
Did you put pieces of wire into the ends so that you could grip them without crushing them?
I have tested wire down to .05mm diameter, just takes more care.

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P.E. Metallurgy, Plymouth Tube

 

[Metalero]

You shall test in final condition, and the properties obtained must be representative of the tube.

If you want properties of the bar, you have to test the bar.