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

( ) (4)
Poisson‟s ratio was assumed to be υ=0.49 (M. Kwiatkowska et al., 2009). Equation 5 was used to calculated indentation
depth of a spherical probe. The indentation depth was used for validation of the mechanical properties of the human skin. The
indentation depth was compared with data obtained during FE modelling (table 1).
For a 2D model the thickness of the model (Fig. 5.) can be determined by calculating the radius of the contact area between
the probe and the skin. This dimension is important because for the difference probes and loads the contact area is also
different.
Figure 5 Contact between the probe and the skin in the FEM Simulation
where b is the thickness of the model. Table 1 shows the thickness of the models used in the FE simulations.
Table 1 The estimated values of the skin effective Young's modulus E [4] and deformation friction contribution.
Experiments
condition
E
[kPa]
Depth of
penetration
[mm]
(Eq. 5)
4
Depth of
penetration
[mm]
(FE model)
Thickness
of the
model
[mm]
D=2mm, load 0.19N 85 1.2 1.6 1.7
D=2mm, load 0.5N 120 1.8 2.1 2.1
D=5mm, load 0.19N 30 1.7 1.4 1.8
D=5mm, load 0.5N 76 1.8 1.7 2
The mechanical properties of the human skin are dependent on the loading and environmental conditions. Mechanical
properties were obtained by trial and error based on the literature data (S. Diridollou et al., 2001) (M. Kwiatkowska et al.,
2009) (Geerligs, 2009) (F.M. Hendriks, 2005) (F. M. Hendriks, 2003) (Bensouilah J., 2006) (Hung A., 2009). In all cases, the
same mechanical properties were used. Different layers have different influences on the model behaviour. The stiffness of the
bottom layers has a high influence on the horizontal displacement of skin during friction test. The middle layers determine
the indentation depth and the “bow wave” effect. The “stick” and “slip” effect is dependent on the stiffness of the stratum
corneum. If the stiffness of the stratum corneum is too high, the probe jumps and the “bow wave” and “stick” and “slip”
effects are small. However, the layers are dependent on each other. In the Table 2 the mechanical properties used in the
model are shown.
Friction of coefficient between probe and skin was obtained from the literature (M. Kwiatkowska et al., 2009). Table 2
shows the main parameters used in the FE simulation.
During the FE simulation only the probe diameter, load, thickness of the model and coefficient of friction were changed.
(5)
(6)