Wire material for Strain Gage application

[Layvinh]

I am in the process of developing wire for Strain Gage application. Generally, this Strain Gage is welded to a steel truss, or steel rib support ( in deep excavations or tunneling) for measuring internal stress within these structures. I wonder if anyone can advise me which wire material is suitable for this purpose?

The basic criteria of wire for strain gage as follows:
1) The diameter should be as small as 0.22 mm
2) The length of the wire approximately 16.5 cm
3) The wire will be fixed and tensioned at both side and could measure 3000 µε of strain without yielding.

Right now I'm doing some experiment with Stainless steel 304 and music wire but I've hard times with stability of strain data.
I would really appreciate any feedback and comments

Regards,
Christian Luis

 

[EdStainless]

I have seen Ni wire used for this (718).
They put it through multiple stress relief treatments first.

Is your 304 high strength? It needs to be.
I would use multiple 600F heat treatments in order to get better stability.

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P.E. Metallurgy, Plymouth Tube

 

[Layvinh]

Thank you for your feedback.
As you mentioned, when selecting materials we consider material strength, and its composition(such like regulated inside ASTM specs.
we used SS-304 piano wire quality wire, but when excite with pulse current, the output signal is not so stable (maybe due to temperature and fixing problems). Do you think Ni 718 has better stability compared to SS? what is the advantages of using Ni? (perhaps you refer to Inconel alloy)

Luis,R&D, Geotech Science

 

[EdStainless]

The 304 wire is not stable austenite, there will be some martensite in it and that amount may not stay constant.
A Ni alloy (718 or 625) in the high strength condition will be very stable, especially after you stress relive it.

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P.E. Metallurgy, Plymouth Tube