These are the modulus from nano-indentating (CSM method) of a SiC composite. Why is the modulus dropping and is this result usable? Which part of the graph gives me an average modulus? Any suggestions on how to improve these results?
Do you have fused silica measurements done before or after the presented ones using the same parameters ? In case the tip area function is not well calibrated you can do it now by running measurements on fused silica standard and recalculating the function and later the measurements.
Grzegorz Cios Thanks for your reply. The indenter was calibrated on fused silica with the same parameters except for the poisson ratio.
If the measurement was done correctly this might be the Indentation Size Effect (https://en.wikipedia.org/wiki/Indentation_size_effect) the material appears to be higher surface hardness and hence higher young modulus at small scale. Normally the curve is monotonically decreasing so I dont really have an explanation for what happens between 0 and 100nm displacement if not that the instrument is not sensitive enough in that range or the total compliance of the instrument is really high.
Another explanation for this can be again a really high compliance of the instrument and of the way the sample is mounted on the sample holder. You might have calibrated with fused silica the compliance of the instrument but if then the fused silica was replaced by your SiC sample that was mounted on the sample holder in a different way then you might experienced a really high compliance between the sample and the holder (Too thick layer of glue, glue with low modulus and in the case the sample is not glued there might be not good contact or not plan parallelity between the two surfaces in contact of sample and holder...)
Have you considered reloading on the same indentation after unloading? This way you would have cancelled any plasticity-like effect. The problem would be that since contact would now be conforming instead of non-conforming, you would need to consider an effective indenter shape. Thus post-treatment would require local profilometry of the resitual indentation.
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