Experimental Force-Displacement curve: different measurement methods
Talking 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?
I'm wondering about this, because I carried this same compression test, 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. I would really appreciate if you know any literature/article discussion this.
Thanks in advance