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

objects smaller than one tenth of a millimeter [9-10], typically 5 to 20 μm. It has
significant influence for research into the microstructure of bone and highly porous
materials. The software STL model Creator [11] was developed in Matlab 2009b for
faster image processing and analyzing of the micro-CT data. This program loads images
in various formats and can create a 3D model in vectored form. For further processing
in FEM systems it is important to export the data. For this purpose the STL polygonal
net format is used. It is necessary to note that on the micro-level the computational
model obtained from micro-CT adequately respects the shape of such complicated
structure. Micro-CT slices were obtained in resolution 700x800 pixels (a total of 1000
slices with pixel size 15 x 15 µm 2 ).
4.2 FEM model
The computational model was created by a finite element method using the system
ANSYS 12. SOLID187 element was used for meshing; it is a 10-node element with
quadratic displacement behavior. Since the high porous structures are very complicated
in shape, it is important to pay attention to the creation of mesh, see Fig. 2.
Fig. 2. a) FEM model of ceramic foam geometry and b) illustration of mesh
It is necessary to have a very fine and accurate mesh for the analysis of local stresses in
such complex microstructure. In addition, more precise mesh is necessary in the places
of stress concentrators. The time of mesh creation mainly depends on size and object
complication. For example, 5.3 million elements and 7.4 million nodes were used for
sample on Fig. 2.
Very good hardware is necessary to have to creation of such complicated models. A
used computer station to calculations was composed from an Intel® Core i7
Processor, a solid-state drive (SSD) and 24GB RAM. This computer station allowed
creation relatively extensive computational models. Despite the fact, the whole structure
(15 mm) was divided to three parts which each of them contains about 7 million
elements.
The computational models were considered as homogeneous isotropic with Young´s
modulus E = 70 000 MPa and Poisson’s ratio ν = 0.3. On the micro-level this ceramic
foam can be considered as homogeneous and linear isotropic [12]. 1 st and 3 rd principal