Page 234 - Handbook of Properties of Textile and Technical Fibres

Engineering properties of spider silk 209

prevents the nonlinearities due to slackening of the strings. The tensegrity systems can
be considered as space structures. Their lightness places them in the same class as
cable and membrane systems. The self-stressing nature, which provides their rigidity,
provides spider webs the mechanism for efficient and economic means of balancing
the stresses induced. An understanding of the interaction of material properties and
structural geometry may shed light on our ability to design the next generation of
ultra-lightweight, large-area space structures.
With the engineering properties experimentally characterized, Ko and Jovicic
(2004) structurally analyzed the spider web and examined the unique combination
of engineering properties of spider silk in comparison with other manmade fibers.
Table 6.4 provides a summary of the engineering properties of the spider silks in
comparison with silk and synthetic polyamide fibers.
To address the influence of different design parameters on spider’s web structural
integrity and complement experimental efforts, the ABAQUS-EXPLICIT finite
element code was used to simulate the static and dynamic properties of the spider
web and to explore the role of material properties and architectural design in its struc-
tural integrity and mechanical performance (Ko and Jovicic, 2004). The spider web
was modeled as an elastoplastic three-dimensional truss structure with a fiber diameter
of 3.57 mm and fully constrained foundation lines. The ductile failure model was based
on a damage-Von Mises plasticity theory with isotropic hardening. These preliminary
results showed that the excellent combination of strength and toughness of a spider silk
offers great potential and superior dynamic characteristics compared to other materials
that have higher tensile strength than that of the spider silk, as shown in Fig. 6.15. The
superior strain energy is especially prominent in the plastic region. This effect was
illustrated using spider silk and poly(p-phenylene benzobisoxazole (PBO)) fiber
webs as examples by subjecting them to impact loading involving deformations up
to the plastic range for duration of 0.1 s by a 2 g bug impacting the web at a velocity
of 1 m/s. The finite element analysis predicted (Fig. 6.16) that the spider web would be
able to stop the impacting bug without failure, while the web made of PBO material
would be perforated.

Table 6.4 Engineering properties of various fibers (Ko and Jovicic,
2004)

Material E L (GPa) E T (GPa) G L (GPa) E L /E T E L /G L
A. aurentia spider silk 34.00
N. clavipes spider silk 12.71 0.579 2.38 21.95 5.34
Bombyx mori silk 9.90 3.81 4.93
Merino wool 3.50 0.93 1.31 3.76 2.67
Nylon 6 filament 2.71 1.01 0.52 2.68 5.21
Kevlar 29 79.80 2.59 2.17 30.81 36.77