Biomedical Engineering Reference
In-Depth Information
180
160
140
120
100
80
60
40
20
0
12
10
8
6
4
2
0
0
100
200
300
400
500
0
Cement Young's modulus (GPa)
(b)
1
2
3
4
5
Prosthesis Young's modulus (GPa)
(a)
14
12
10
8
6
4
2
0
0
100
200
300
400
500
Prosthesis Young's modulus (GPa)
(c)
12.8
Results from stress analysis of the artificial hip joint using finite
element analysis (Prendergast
et al
., 1989). (a) The maximum stress
in the stem as a function of the Young's modulus (
E
) of the stem
material. (b) The maximum stress in the bone cement as a function
of the
E
value of the cement. (c) The maximum stress in the cement
as a function of the
E
value of the stem. All results obtained for an
input load of 3 kN at the femoral head.
typical hip joint. The figure shows the maximum stress experienced in the
stem part of the implant, that is, the part which inserts into the femur. The
applied force is assumed to be 3 kN, which would be the typical maximum
force during walking. By varying the elastic modulus of the implant material
we can see how the maximum stress changes when different materials are
used. Such analyses have been performed for many different AHJ designs
and, despite some variations, they all present the same picture: the stress
increases with the elastic modulus (Young's modulus) in a manner which is
close to a simple proportionality.
Why should this be? For a component of constant shape, loaded with a
constant force, we would not expect the stress to change with the young's
modulus of the material, at least provided the overall deflections are quite
small, which they will be in this case. The reason for the effect seen here
is that we are dealing with a structure containing more than one material.
