ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

current study to explore the effect of friction variations on pile-up using a 3D model of
the Berkovich tip with the finding that less friction leads to greater pile-up. The 3D
modelling in this study suggests that not only may the pile-up height be underestimated
by neglecting to consider friction between the indenter and the bone, but also the shape
of the residual pile-up may differ (as demonstrated in Figure 5).
Finally, we note that the models used in this study adopt idealised representations of the
bone tissue constitutive behaviour. It is established that bone exhibits anisotropy with
respect to tissue-level mechanical properties [5]. Bone tissue is also known to exhibit
time-dependent (e.g. viscoelastic [3]) properties, which were not addressed in this study.
6. CONCLUSIONS & FUTURE WORK
This numerical study of high-load nanoindentation of bone tissue suggests that threedimensional
FEA of bone nanoindentation, while being more computationally
expensive than 2D axisymmetric models, may be advantageous in investigating the
post-yield behaviour of bone tissue.
We are currently collecting experimental data on the high-load nanoindentation of
trabecular bone samples, including observations of pile-up. This data will then be used
to evaluate existing proposed constitutive material models to describe the post-yield
properties of trabecular bone tissue, including appropriate consideration of friction
between the bone and indenter, and pile-up prediction.
7. REFERENCES
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3. Tai, K., Ulm, F., and Ortiz, C. Nanogranular origins of the strength of bone. Nano
Lett, 2006, Vol. 6, 2520-2525.
4. Mullins, L. P., Bruzzi, M. S. and McHugh, P. E., Calibration of a constitutive model
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5. Carnelli, D., Gastaldi, D., Sassi, V., Contro, R., Ortiz, C. and Vena, P. A finite
element model for direction-dependent mechanical response to nanoindentation of
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numerical simulations of bone nanoindentation. J. Mech. Behav. Biomed. Mater
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nanoindentation experiments on thin films using finite element method. Thin Solid
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