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

was modelled as linear elastic, where Young’s Modulus, E = 4.2MPa and Poisson’s
ratio, v = 0.3. Uni-axial compression force was applied on the platen using the same
data applied to the experimental testing (Figure 3). All degrees of freedom of the platen
were restricted, except in the axis parallel to the direction of the force applied. It was
assumed that the bone material supporting the bottom surface of the cartilage was
significantly stiffer than the cartilage tissue and hence, all degrees of freedom of the
nodes on the bottom surface were restricted. Interactions between the platen and the
cartilage surface were modelled as hard normal contact with no penetration and
frictionless tangential contact. For comparison, an axis-symmetric flat surface cylinder
model with the same thickness and diameter was analysed using the same material
properties, boundary conditions and loading conditions (Figure 3).
Figure 3 Diagram of the flat surface finite element model set up. Force was applied on the platen and the
bottom surface of the explant was restricted in all degrees of freedom (left) Force loading applied in
model and experimental testing, a maximum force of 11.58N was applied with a ramp of 0.1s. Force was
held constant at 11.58N for 0.4s and the explant was unloaded again to 0.1N over 0.1s (right)
4. RESULTS
For the explant specific curvature model, maximum surface displacement at contact
between the platen and explant was predicted to be 0.185mm and the maximum
principal stress was 0.236MPa. Results for the flat surface model were found to be
0.047mm and 0.030MPa (Figure 4).
Figure 4 Comparison of maximum principal stress and nodal displacement predicted at contact point
between the platent and explant
Deformation pattern predicted by the flat surface model displayed uniform transverse
isotropy across the explants, as local deformation decreased linearly with depth from
0.047mm to 0mm. Maximum principal stress experienced across the tissue ranged from
-0.0012MPa to 0.003MPa. No significant shear stresses or shear patterns was observed.