I am trying to find a way of using load - displacement data to find the localized poison's ratio of bone. Literature says we generally take 0.3 for cortical lamellar region but can we validate it.
I don't think so. Nanoindentation can give a value for "Young's modulus" (I've put that in scare quotes because just what elastic modulus the usual method gives you is a bit nebulous, though it's closest to the uniaxial tensile/compressive modulus), but can't tell you anything about the other moduli, lateral strains or Poisson's ratio.
One way is to performed a tangential stiffnesses measurement during normal indentation. the ratio between tangential and normal stiffnesses can be related to Poisson’s ratio.
Better to use ultrasonic models, if you want for bulk material...
Classical nanoindentation done perpendicularly to the surface gives you the "indentation modulus" M that is linked to the young modulus E and the Poisson's ratio nu for an isotropic material following the well known results from Hertz: M = E/(1-nu^2), after taking the indentation modulus of the indenter into account. For an anisotropic material, like bone I guess, it's linked to most of the elastic constants like the shear moduli, in plane elastic modulus and Poisson's ratios like it has been well described by Delafargue and Ulm (Int. J. Sol. Struct., 2004), when the indentation is done parallel to one of the principal direction of anisotropy, and Vlassak and Nix (J. Mech. Phys. Sol., 2003) in any case.
As said by Luc Carpentier, if your material is isotropic, you can measure the Poisson's ratio by doing one classical indentation (normal to the surface) and an other one where your load is tangential to the surface (not easy to do in a classical nanoindenter as far as I know). You can read something about this in the paper from Le Rouzic et al (Material Letters, 2012) but it has been done by an indentation like technique that is not nanoindentation.
If your material is anisotropic, first you don't have just one Poisson's ratio. Second, it seems to me difficult to measure them in one point but you can for example have an idea on a broader area like what has been done by Jäger et al (2 articles in Comp Part A, 2011) on the wood cell wall.
Last, US or RUS can in fact gives you access to all the elastic constants but usually Poisson's ratio are not measured accurately as the measurement are not enough sensitive to them and it will be an average value on the whole sample not in a localised point (except if you have an acoustic microscope but even in that case, to my best knowledge, you won't be able to do all the required measurement for the indentification of the Poisson's ratio.
One solution could be to use DIC measurements of the strain fields under a compression test under an optical microscope (see Hild and Roux, Strain, 2006) or 3D imaging (tomography or micro-MRI) like Benoit et al (J. Biomech, 2009).
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