buletinul institutului politehnic din iaşi - Universitatea Tehnică ...

Bul. Inst. Polit. Iaşi, t. LVIII (LXII), f. 4, 2012 245
The mechanical properties of the elements of the analyzed assembly,
required for finite element analysis in ANSYS, are presented in Table 1.
separati
on
F
F
Fig. 1 – Traction loading of the assembly bone-implant.
Table 1
Mechanical properties required for FEA
Materials
Elascicity modulus
E [MPa]
Poisson
coefficient, ν
Austenitic stainless steel 1.93⋅10 5 0.31 7.86⋅10 -6
Porous bone 100 0.27 1⋅10 -6
Periosteum 15.3⋅10 3 0.28 1.8⋅10 -6
Compact (cortical) bone 17.5⋅10
3
0.28
-6
2⋅10
Density 3
ρ [kg/mm ]
The first stage of the numerical analysis with finite element was to
import the assembly CAD model and to declare all the materials involved in
analysis. Thus, the uased materials were: austenitic stainless steel for the screw,
porous bone for the internal layer of the lower epiphysis of tibia, periosteum for
surface layer of tibia and compact (cortical) bone for lower layer of tibia
diaphysis. The next stage was to declare the contact between elements. This
operation was done automatically, the software ANSYS identifiyng the surfaces
in contact and declaring links.
Numerical analysis with finite element continued by dicretizing the
assembly into finite elements. Discretization was done automatically, using
tetrahedrical elements, respectively “10-Node Tetrahedral Structural Solid”.
Initially, was tried manual discretization of the assembbly, but certain regions of
the threaded zone could not be discretized due to assigning too small
dimensions for discretized elements. Thus, the automatic discretization was
chosen. Another reason for chosing automatic discretization is that the calculus
requirements are increasing exponentially at the same time with decreasing the