Bio-inspired, Flexible Structures and Materials - Biotechnologies and Biomimetics for Civil Engineering - page 281

Table 12.2 Comparison of
engineering and natural
design principles

Engineering principles Natural principles

Light materials Anisotropy

Light structures Heterogeneity

Hierarchy

Light systems Multifunctionality

Adaptability

again and the bird may transport the pollen to another Strelitzia flower where
pollination takes place.
The flapping mechanism of the S. reginae is particularly suitable for a tech-
nological transfer because it can be triggered at any time by applying an external
mechanical force at a specific location of the structure. When loaded this way it
shows what is defined in engineering terms as a distinct tipping failure. This
phenomenon permits a series of experiments with which the mechanism can be
investigated precisely in order to learn more about its functions.
In this case the abstraction can take place via a reduction principle. While doing
so, parts of the plant that may not have anything to do with the basic kinematics
are gradually cut away. Hereby it becomes clear, that only individual halves of the
leaves with directly connected reinforcing strip are responsible for the flapping
mechanism (Fig. 12.3 ). Such a system can easily be imitated and simulated with
physical models (Fig. 12.4 ).
This biological principle unveils an elastic flapping mechanism which is
transferrable to technical fields of application. In contrast to common kinetic
structures which work on the basis of locally arranged hinged, jointed and angular
connections, the biomimetic approach works on the basis of pliability of large
surfaces. This enables a wide range of adaptation and the wear of material at the
joints and hinges can be avoided. This principle represents a paradigmatic shift in
civil and structural engineering wherever it was previously recommended to avoid
any form of structural failure. The actual mechanism behind this movement is
known as lateral torsional buckling in engineering, a so-called 'failure mode' that
engineers generally try to avoid by sizing structural members to adequate stiffness.
The physical model in Fig. 12.4 shows the effect of lateral torsional buckling in a
constellation as can be found in the plant's mechanism. In the Strelitzia, however,
this failure mode has no negative connotation but simply utilises as fundamental
motion principle for a highly effective compliant mechanism. In fact, S. reginae
cleverly exploits the potential of an unsymmetrical bending motion as an inte-
grative part within a reversible deformable structure with multiple deflected
equilibrium positions.