Biomedical Engineering Reference
In-Depth Information
Figure 6.12 The experimental data versus finite element results (error bar indicates the range of
readings). The simulation conditions for Test 1: U y = 2.5 mm, R = 3 mm, and Depth = 5 mm; and
for Test 2 : U y = 1 mm, R = 2 mm, and Depth = 4 mm
of at least 20 cycles were recorded and arithmetically averaged. In the first test (Test 1),
the parameters were as follows: applied displacement U y = 2.5 mm; diameter and depth
of the lump were 6 and 5 mm, respectively. Whereas in the second test (Test 2), the
applied displacement was U y = 1 mm with a lump diameter and depth of 4 mm. The
experimental results are compared with finite element results and shown in Figure 6.12.
6.6 Discussion and Conclusions
The results obtained from the finite element analysis of a mass embedded in soft tissue are
presented in Section 6.4 and show that the pressure distribution at the contact surface is
influenced by several parameters, such as size, depth, and stiffness of the lump, as well as
the applied force. The nonlinearity of the response with respect to these parameters is also
shown. This nonlinearity can be attributed to both the material nonlinearity of soft tissue
and geometrical nonlinearity, which happens for large strains. The response to variation in
applied load, as depicted in Figure 6.7, shows that although an increase in grasping load
causes an increase in the maximum pressure, the shape of curve remains unchanged. In
addition, the amount of area that each curve covers remains almost constant. This could
be a distinctive sign that differentiates the effect of variations in load from the variations
in the size and depth of the lump. It is shown that although the ratio of the Young's
modulus of the lump to that of the tissue is an effective factor, the stress profile remains
almost unaltered for ratios higher than 10. On the other hand, the pressure ratio is highly
sensitive to the variation in stiffness of the lump for E L < 10 E T , which potentially is
helpful in detecting lumps in their early stages.
The thickness of tissue clearly affects the stress profile; however, for a specific arrange-
ment of lump and tissue, the increase in tissue thickness is equal to the decrease in lump
size. Therefore, it is possible to combine both parameters into one variable, in order to
Search WWH ::




Custom Search