Mechanical test: influence of displacement measurement method on the load-displacement curve

[Rodrigo Benitez]

Hi engineers, I don't know if this is the best forum to post this question, but here it goes.

Regarding about a compression test on a sample with an hydraulic press: what's the real difference between using 4 LVDTs to measure displacement (like the one of the photo below) compared to using only the actuator's internal displacement transducer? Would it cause a higher displacement measure to use the second method, and hence, a loss in stiffness? This photo is from another author:

I'm wondering about this because I carried out this same compression test of the photo, but measuring the displacement by the second method, and I'm thinking it might be the cause of the big nonlinear-elastic part of my experimental curves:

The black lines are FEM modelling. As you can see, they are much stiffer then the experimental curves. I would really appreciate if you could share any knowledge/literature/article discussion this.

Thanks in advance

 

[MintJulep]

What is the material?

What are the assumptions about the material that are built into your FEM model?

The independent displacement transducers will measure only (almost) the displacement of the test specimen.

The internal displacement transducer of the actuator will detect and report any displacment of the test machine + the test specimen.

 

[Rodrigo Benitez]

I asked the same thing on the Ansys student's forum:

https://forum.ansys.com/discussion/...nt-curve-different-measurement-methods#latest

Tell me what you think of it.

- Rodrigo

 

[MintJulep]

I think that the person who responded on the ansys forum and I agree exactly.

 

[Rodrigo Benitez]

Thanks for your answer. This problem is solved.