Page 351 - Anthropometry, Apparel Sizing and Design

344 Anthropometry, Apparel Sizing and Design

F (gf/cm)
50

40

30

20
Ds
10

8.5 17.0 25.5 34.0 42.5 51.0
De E (strain) %
Fig. 13.6 The graphical scheme of finding the values Δσ and Δε in the neighborhood of
ε¼ 20% by means of Kawabata Evaluation System.

dP=dε ¼ dP=dσ Δσ=Δε, (13.3)

where dP/dσ is the derivative calculated from the curve P(σ), and Δσ/Δε are the values
calculated from the stress-strain, for example, obtained as curve F-E by the Kawabata
Evaluation System KES-FB1. Fig. 13.6 shows the graphical scheme of Δσ and Δε
calculation.
The module of compression ability M comp can be calculated by

M comp ¼ P 20% =20, (13.4)
where P 20% is the pressure under the materials after its elongation of 20%. For
example, knowing the values found graphically from Fig. 13.6 σ(20%)¼15 and
Δσ/Δε¼7/6, and the pressure on soft tissue, the M comp is 33.
The module of compression ability was used for a new classification of compres-
sion materials. The boundaries of compression garments were chosen as 0.4, 1.3, 2.0,
3.3kPa. The values 1.3 and 2.0kPa correspond to the appropriate and maximum
values for daily clothes (Kawabata, 1980). The value 3.3kPa corresponds to the max-
imum pressure recommended for sportswear, as well as for vascular diseases and
after-burn therapy. Higher values are rendered as a strong effect and can be used only
for medical purposes to treat the lymphatic system (http://www.instron.us/en-us/prod
ucts/testing-systems). The strain of 20% for the less extensible materials could pos-
sibly give a pressure exceeding the permissible value of 3.3kPa, while the most
extensible ones did not even produce a minimum pressure of 0.4kPa. Thus based
on the module of compression ability M comp and boundary values of pressure for
the garments, the schedule of compression garments and their applications includes
four groups, as shown in Table 13.5.