Poroelastic nanoindentation analysis

Just published in this month's Journal of Materials Research--a study on poroelastic nanoindentation characterization for hydrated bone samples.  Poroelastic problems are notoriously difficult to incorporate into routine materials characterization due to the paucity of problems with closed-form solutions.  However, in some cases, a master-curve does exist and parameter identification can be accomplished without requiring inverse finite element analysis and optimization for every condition.  The abstract follows, linked from here .

Poroelastic nanoindentation responses of hydrated bone, J. Mater. Res. 23 (2008) 1307.

Indentation techniques are used for the measurement of mechanical
properties of a wide range of materials. Typical elastic analysis for
spherical indentation is applicable in the absence of time-dependent
deformation, but is inappropriate for materials with time-dependent
creep responses active in the experimental time frame. In the current
work, a poroelastic analysis—a mechanical theory incorporating fluid
motion through a porous elastic network—is used to examine spherical
indentation creep responses of hydrated biological materials. Existing
analytical and finite element solutions for the poroelastic Hertzian
indentation problem are reviewed, and a poroelastic parameter
identification scheme is developed. Experimental data from
nanoindentation of hydrated bone immersed in water and polar solvents
(ethanol, methanol, acetone) are examined within the poroelastic
framework. Immersion of bone in polar solvents with decreasing polarity
results in increased stiffness, decreased Poisson’s ratio, and
decreased hydraulic permeability. Nanoindentation poroelastic analysis
results are compared with existing literature for bone poroelasticity
at larger length scales, and the effective pore size probed in
indentation creep experiments was estimated to be 1.6 nm, consistent
with the scale of fundamental collagen–apatite interactions. Results
for water permeability in bone were compared with studies of water
diffusion through fully dense bone.