Optimization Potential of the Method - Preventive Biomechanics - page 348

Fig. 7.81 Comparison of stress when interchanging the female and male B OSS -Models: a female
Boss-Model on cushion optimized for the male mode and b male Boss-Model on cushion
optimized for the female Boss-Model
tail bone. The compressive stress S 22 at the tail bone tip was three-fold the stress at
the ischial tuberosity, and the shear stress S 23 was eight-fold the stress at the
ischial tuberosity, compared to the stress at the tail bone tip. All stress values, with
the exception of those of S 22 , showed changing signs along both paths. For
example, tissue direct stress S 33 was -0.08 MPa (compression) at the tail bone tip
and +0.05 MPa (tension) at the ischial tuberosity.
7.3.3 Implications of Interchanging the Female and Male Model
Tissue stress was investigated when interchanging the human Boss-Models
(female Boss-Model interacting with the seat cushion optimized for the male Boss-
Model and vice versa). The blue bars in Fig. 7.81 show the male/female buttock
tissue stress values, due to interaction with the non-optimized seat cushion (initial
geometry according to Fig. 6.30 b in Sect. 6.3.4.1 ) . The green bars represent the
male/female buttock tissue stress values, due to interaction with the optimized seat
cushion. The red bars represent tissue stress as a result of mechanical interaction of
the male model with the seat cushion optimized for the female Boss-Model, and
vice versa.
Figure 7.81 a shows that buttock tissue stress (with the exception of S 23 ) of the
male Boss-Model, interacting with the optimized seat cushion, was clearly reduced
(cf. green bars) compared to the other two variations.
Tissue stress due to interaction with the cushion optimized for the female Boss-
Model (red bars) was always lower (with the exception of tensile stress S 22 as well
as both (negative) shear stresses S 12 and S 13 ) compared to tissue stress due to
interaction with the non-optimized cushion (blue bars).