Solid friction reduction on the skin of the sandskink
Sandskink (Scincus scinus)
Ingo Rechenberg & Abdullah Regabi El Khyari
Hypothesis of the Bionicists
Swimming in the sand under a
dune, demonstrated by the sandskink of the Sahara, is certainly much
more exhausting than swimming in the water. Therefore, if energy
reduction is the main objective of biological evolution, the scales of
the sandskink should have a mechanism to reduce the solid friction.
Really, the surface of a sandskink looks highly polished.
Experiments in the desert Erg Chebbi (Morocco)
In the summer 2000 we* measured in the Sahara for
the first time the sand friction coefficient on the surface of the sandskink.
The idea for the construction of a dynamic friction meter was the principle
of an hour glass. Out of the cannula of the glass
vessel a sand stream is flowing down to the inclined test surface
Definition and measuring of the dynamic friction coefficient μ
If the inclination angle of the test surface isn't too small the sand is flowing
on. The tangent of the angle for which the sand stream stops is called the
dynamic friction coefficient. For narcotizised and for killed sandskinks we
obtained a sand gliding angle of 21°. When we repeated the experiment in the
sommer 2002 we obtained for an absolutely undamaged animal even a critical angle
20° Sand flow stops
22° Sand flow is moving
Parallelly to the above
experiments we measured the critical sand sliding angle for some technical
materials. The results:
polished steel = 25°
glass = 28°
nylon = 30°.
Sand friction on the surface of the sandfisch compared with the
friction on other materials
Quintessence of the experiments: Biological evolution
has worked out a solution with minimum solid friction. The technical
imitation of the skink surface gives the chance to develop a new
generation of sliding-bearing materials. For instance: Disciples of
the sport of sand-boarding may use it.