Page 213 - Handbook of Properties of Textile and Technical Fibres

190 Handbook of Properties of Textile and Technical Fibres

1.0
Diameter: 4.2 μm; L0: 2.53 cm
Tensile speed: 0.002/s

0.010

Stress(GPa) 0.5 F (N)

0.005

Y.P.
Fy

εy

0 0 0.05 0.10 0.15 0.20
Strain
Figure 6.4 Tensile property of single Nephila clavipes spider dragline fiber (Ko et al., 2004a).

extensibility of approximately 500%, which develops substantial force after
100%e200% extension (Vollrath, 2000; Vollrath and Edmonds, 1989; K€ ohler and
Vollrath, 1995). Draglines of N. clavipes (golden silk spider) and Argiope aurantia
(black and yellow spider) are among the strongest spider silks that we know.
Fig. 6.4 shows the average tensile stress-strain curve of N. clavipes spider dragline
silk from 10 replications, wherein the sigmoidal shape stress-strain curve is similar
to that of the A. aurantia spider. With an average initial modulus of 12.71 GPa, the
failure stress of the fiber is 0.85 GPa at 20% breaking elongation. Similar to that of
the A. aurantia spider a yield point is detected at about 5% strain. These results
show that the maximum properties of spider silk may differ from one species to the
other with A. aurantia spider making stronger silk than the N. clavipes spider in
this case. The strength of the dragline of N. clavipes obtained by forcible silking
was reported to be about 8 g/denier and the strength of the dragline of A. aurantia
was approximately 12 g/denier (Zemlin, 1968). Tensile tests conducted on the drag-
lines of the Queensland Bird-Catching Spider (Nephila maculata) showed a nominal
fracture strength of about 1100 MPa, which was independent of the spider size, and the
tests made on draglines aged for 21 days showed only a moderate deterioration in
properties although a marked change occurred in the initial part of the stress-strain
curve (Griffiths and Salanitri, 1980). Gosline et al. (1986) found the dragline silk taken
from the web of the spider Aruneus sericatus has a stiffness of about 10 GPa and the
maximum stress achieved prior to fracture is about 1.4 GPa with an extension of about
30%, while the viscid silk is extremely extensible with an initial modulus of elasticity
only about 3 MPa, a breaking strength of 3 MPa, with an extension of 200% or more.
Cunniff et al. (1994) tested the dragline silk from N. clavipes spider. Their tensile tests
indicated values for the average initial modulus; ultimate tensile strength; and ultimate