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

An algorithm was written (Matlab, R2009a, MathWorks, Natick, USA) to extract the
coordinates of the nodes along the outer edges of the FE and experimental models.
Interpolation was used to find nodes in the two models with the most similar y values.
The coordinates of these similar nodes were compared and the difference was found
between their x values. This difference was applied as a displacement boundary
condition to the node in the FE model. This process was repeated for each node along
the outer edges of the model in the radial direction. Thus in its deformed state, the FE
model had the same geometry along its outer edges as the experimental model. A
variable displacement was applied to the outer edges of the model that ensured the
deformation of the model was the same as that observed experimentally.
Two variations of the FE model were developed: the “bridges” model and the “sheath”
model. This allowed a comparison of the two tissue models postulated in the
literature 1,5 . Details from these two model variations are shown in Figure 1: in the
bridge model, bridges join the two in-plane lamellae. In the sheath model, the bridges
are part of a sheath network that surrounds the fibre bundles. A fine layer of sheath
elements is included inbetween the sectioned and in-plane lamellae.
Figure 1 - Detail of FE models showing bridge variation (left) and sheath variation (right).
For both models, the relative material properties of the bridges/sheaths were varied.
The stiffness was considered relative to that of the lamellae in the x direction. The
bridge/sheath elements were assigned isotropic linear elastic material properties. The
stiffness was varied by orders of ten, from one order of magnitude lower than the
lamellae in the x direction (Elam,x:Ebridge = 1:0.1) to five orders of magnitude higher
(Elam, x:Ebridge = 1:100,000). The internal geometry of the deformed FE model was
compared to that of the experimental model.
4. RESULTS
In plane lamellae
4.1 Experimental Results
Sectioned lamella
Cross bridges
Cross bridges integrated
into sheath network
surrounding fibre bundles
During the testing of the five specimens, common characteristic features were observed,
such as puckering of interlamellar boundaries and the thinning of tissue in localised
areas, as highlighted in Figure 2.