Hello all,
I'm in the processes of extracting the stress and strain data points from a load displacement curve resulted from Nanoindentation simulation of a single crystal. As you might know, to be able to use Hertz theory for this purpose, I should run the simulation with many loading and unloading steps and apply the Hertz equations in unloading sections, which are elastic portions of the load displacement and are consistent with the Hertz theory, to extract data points for the stress-strain curve.
I have searched a lot and found several papers from Prof. kalidindi regarding this issue but when I apply those methods to extract the simulation stress-strain curve and compare it with the experiments, they do not match! Attached I added a picture of the Comparision.
So, I'm wondering if anyone knows about the procedure which I should follow to extract stress-strain data points that can help me to resolve this issue.
Best,
Sajjad
Two points to reflect about:
1) in real NI experiments you can extract stress - strain curves only from indentations performed with spherical tips, infact the berkovic indenter tip is a self similar geometric shape, this means the strain levels are constants regardless the penetration depth and so you can not test different levels of strain; this doesnt happen with the spherical indenter that is NOT self-similar. I dont know in your experiments what indenter tip you used.
2) Hertzian theory is the basic theory and relies only on elasticity, it doesnt take into consideration any plastic deformation, compliance of your system, ... the nanoindenter software might instead take into consideration different indentations depths such as hmax, ha, hc... for plotting the results. It might be needed to get the ha value into your calculations to get better agreements ...
Hello Enrico
In the experiments we used the spherical shape indenter.
I believe the software used elastic portion of the displacement (h_e) since the software also uses the hertz theory to calculate the stress-strain curve which relies on the elastic portion of the load-displacement curve.
I'm also replicating the experiment procedure to calculate the stress-strain curve using crystal plasticity simulations and a MATLAB script, but the script that I have developed is not stable. So, the numerical results are not in a good agreement with the experiments.
I'm searching for any numerical procedure based on the Hertz theory to calculate the stress-strain curve using the load-displacement curves.
Thank you for the aswere.
Sajjad
As far I know all AFM software (WSXM, NanoscopeAnalysis, Gwyddion) allow to extract all pictures/diagrams/data as ASCI.
Hello Janusz
I believe you are right but the point is that I want to replicate the experiments using crystal plasticity calculations. So, I'm not using any AFM software to extract stress-strain data.
Sajjad
Dear Saijad,
I read now the additional details of your experiemnts and i see you are already in a more advanced state that what i previously thought.
It sounds to me more of a convergence prblem in Matlab that anything else and unfortunately i dont have any special recommendation on how to approach it or how to best fit the experimental results, I dont think there is any partciular fitting based on the hertz theory.
regards
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