Abstract: It is known that the tribological behaviors of snake skins are contributed by the synergistic action of multiple factors, such as surface morphology and mechanical properties, which has inspired fabrication of scale-like surface textures in recent years. However, the coupling effect and mechanism remain to be elucidated. In this work, the morphology and mechanical properties of the scales from different body sections (leading body half, middle trunk and tailing body half) and positions (dorsal, lateral and ventral) of Boa constrictor and Eryx tataricus were characterized and compared to investigate the corresponding effects on the tribological behaviors and to probe the possible coupling mechanism. The morphological characterizations of scanning electron microscopy and atomic force microscopy revealed sig-nificant differences between the two species that the scales from Boa constrictor are rougher in general. The mechanical properties measured by nanoindentation corroboratively demonstrated substantial differences in elastic modulus and hardness. Interestingly, the ventral scales with lower surface roughness, together with relatively larger elastic modulus and hardness, manifest higher friction coeffi-cients. A “double-crossed” hypothesis was proposed to explain the observed coupling effect of morphology and mechanical properties on friction, which may afford valuable insights for the design of bionic surface with desirable tribological performance.

Key words: coupling effect, friction coefficient, morphology, snake scales, bionics, mechanical properties