Page 179 - Handbook of Properties of Textile and Technical Fibres

156 Handbook of Properties of Textile and Technical Fibres

Silk is a visco-elasto-plastic material; its properties have been studied with relaxa-
tion tests by Parthasarathy et al. (1996) and also cyclic loads (Figs. 5.3, 5.8, and 5.9).
The influence of the different compoundsdfibroin and sericindon the mechanical
behavior is difficult to over emphasize. Fig. 5.9 shows a comparison between the
stressestrain curve of an industrial yarn and of a single fiber, the fracture morphology
of which is presented in Fig. 5.10 (Jauzein, 2010; Dinh, 2010). It can be observed that
sericin and the associated yarn structure modify the curve profile: Type II is observed
for the degummed fiber and Type III for the industrial yarn (i.e., a few fibers embedded
in a common sericin sheath). Nevertheless, if the mechanical tests of an industrial yarn

700
600

500
Stress / MPa 400

300

200

100
0
0 5 10 15 20 25 30
Strain / %
Figure 5.8 Effect of cycling loads on Bombyx mori silk.

100
90
80
Load / arbitr. relative unit 60 Textile yarn
70

50
40
Degummed yarn
30
20
10
0
0 5 10 15 20 25 30
Strain / %
Figure 5.9 Comparison between industrial yarn and degummed industrial fiber normalized.