Biomedical Engineering Reference
In-Depth Information
Fig. 7.17 Defining of contacts between ICU elements: ( a ) contact between bone screw 1 and bone 2,
( b ) contact of bone screw head 3 and bone plate 4, ( c ) contact between bone screw 5 and locking
screw 6, ( d ) contact between vertebra 7 and intervertebral disc 8
*.sat file. But in some cases, when the CAD file is imported into the simulation
environment, some valid contacts may miss, while unwanted others can be present.
So, for simulation rigor, the mechanical connections between the assembly's ele-
ments were manually declared. Overall, the connections between the intersecting
elements were materialized into 24 bonded type connections.
Defining of accurate contacts represents a very important factor in stress-strain
evaluation [ 50 ]. The contacts between the bone screw threads and the conjugated
bone interface (see Fig. 7.17a ) were set as bounded in order to simulate a physical
contact behavior. In the same way, the contacts between the bone screw head and
the bone plate (see Fig. 7.17b ), and between the bone screw and locking screw (see
Fig. 7.17c ), were established. The contacts between vertebrae were declared through
the elastic elements: intervertebral disc, facet joints, and interspinous ligament (see
Fig. 7.17d ).
The material assignation represents a mandatory condition for static structural
analysis. In order to achieve valid results, the materials declared in the simulation
have to assure the same mechanical properties as the natural ones. In the simulation
environment some material types were presented in the database, while others
(bone, disc, and ligament) were declared accordingly to the literature [ 13, 20, 68 ] .
The materials selected for the structure's components are:
Spongy bone for the internal vertebral bodies
Titanium alloy Ti-6Al-4V for bone screws and cervical bone plate
Stainless steel for locking screws
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