Data from: Nanoindentation methods for viscoelastic characterization of stiff porous materials

Background Modifying the mechanical properties of the solid phase of a
porous material, in this study calcium-silicate-hydrate, is frequently
possible by changing synthesis conditions, but changes in these conditions
can also influence porosity, which in turn may affect the mechanical
properties of the porous material. Experimental methods to decouple
porosity from the viscoelastic properties of the porous material will aid
in optimization of the structure of the solid phase to achieve the desired
mechanical properties.   Objective Explore different
nanoindentation techniques in order to determine the viscoelastic
properties of the solid phase (without the affect of porosity) of a stiff
porous material via experimental methods alone.   Methods
Compacted pellets of calcium-silicate-hydrate were prepared with different
porosity and subjected to three nanoindentation techniques to determine
viscoelastic behavior and the influence of porosity: dynamic, stress
relaxation, and creep. Results of the porosity and of the viscoelastic
behavior measurements were analyzed with a reverse-micromechanics model to
determine viscoelastic properties of the solid phase, which has not been
achieved previously for calcium-silicate-hydrate. These methods can be
used in development and refinement of materials to determine how changes
in the solid phase (e.g. molecular structure) influence viscoelastic
behavior while considering the effect of porosity.   Results
Dynamic nanoindentation was found to be unreliable for the stiff material
studied in this work. Normalized stress relaxation and creep data were
found to be independent of porosity. Reverse micro-mechanics modeling
allowed for characterization of the creep modulus that is consistent with
other studies that used computational or synchrotron x-ray methods to
characterize mechanical properties of the solid calcium-silicate-hydrate
phase.   Conclusion Creep experiments provide more reliable data
than dynamic or stress relaxation experiments. When the porosity is known,
reverse-micromechanics modeling can be used determine the creep modulus of
the solid phase and thus be used to predict creep modulus of a composite
with an arbitrary porosity. If the porosity is not known, the viscoelastic
properties of the solid phase can still be compared to each other using a
normalized creep modulus that is independent of porosity.