Tribological Properties And Biomimetic Studies On Ventral Scale Structures Of Three Snakes

Currently,more than 30% of the world’s energy consumption is produced in the form of friction and wear;China’s yearly economic loss due to friction and wear ranges from 2% to 7% of GDP.At present,the working environment of machinery and equipment is increasingly complicated,and the service conditions of the parts are increasingly demanding;consequently,the requirements for enhancing the friction performance of the parts are increasing.In nature,the ventral scales of snakes have been in contact with the environment for a long time which evolved non-smooth surfaces with excellent frictional properties,allowing for effective crawling movements in a range of settings including grass,trees,deserts,and swamps.In order to design non-smooth surface with excellent friction characteristics and suitable for a variety of working conditions,this paper using Dinodon rufozonatum,Elaphe carinata,and Boa constrictor as biological models,investigated the friction regulation and wear mechanism based on the surface morphology characteristics of snake ventral scales.Based on this,we designed the bionic non-smooth surface.In this study,we studied the association between the macroscopic morphology of ventral scales and individual factors and lifestyles.The macroscopic morphology and microstructure of the ventral scales of Dinodon rufozonatum,Elaphe carinata,and Boa constrictor were studied,and the characteristic dimensions of the ventral scale surface microstructure were statistically assessed.The results demonstrated that the macroscopic dimensions of the ventral scales and the micro-convex structure of the scale surface varied with the position of the ventral scales,and the macroscopic morphology of the ventral scales and the micro-convex structure of the scale surface exhibited interspecific variation.The differences in shape,size,and transverse and longitudinal proportions of the ventral scales reflected the changes in the macroscopic morphology of the ventral scales.The differences in scale surface microstructure were reflected in the double-ridged micro-convex structure of the ventral scale of Dinodon rufozonatum,the more prominent platform features of the ventral scale of Elaphe carinata,and the microscale structure and convex ridges on the surface of the ventral scale of Boa constrictor.In this study,the material mechanical properties of snake ventral scales were studied.To investigate the apparent mechanical properties of the abdominal scales,the elastic modulus,hardness,and creep of the ventral scales of three snakes(Dinodon rufozonatum,Elaphe carinata,and Boa constrictor)were measured using a nanoindentation instrument.Additionally,the contact angle and nano adhesive force of the ventral scales were measured using a contact angle measuring instrument and an AFM.The results demonstrated that the elastic modulus and hardness of the inner layer of the three snake ventral scales were less than those of the outer layer,and the water contact angle of all three snake ventral scales was larger than 90°,indicating that they were all hydrophobic surfaces.The adhesion force on the top of the convex body of the three snake ventral scales was less than the adhesion force between the convex bodies,with the adhesion force of the ventral scale of Dinodon rufozonatum being the smallest and the adhesion forces of Elaphe carinata and Boa constrictor being comparable.In this study,the cross-scale frictional characteristics of snake ventral scales were examined.The effects of normal load F,sliding speed V,and sliding angle A on the coefficient of friction COF of the ventral scales at each scale were analyzed.The findings of the macroscale friction test indicate that adhesion,mechanical engagement,plowing,and elastic hysteresis dominate the frictional substrate made of the grinding ball and the ventral scale,whereas the COF of the ventral scale is affected by F and V.In the meantime,the ventral scale demonstrates frictional anisotropy.In micron-scale friction,adhesion and hysteresis forces were primarily responsible for the tangential resistance between the scratch head and the ventral scale.The COF of the ventral scales of the three snakes was less impacted by V and rose with F,whereas A had less of an effect.In ultramicroscopic scale friction,the tangential resistance is primarily adhesion and mechanical engagement,and the friction anisotropy generated by the AFM probe sliding on the scale surface micro-convex was due to the probe climbing different inclination slopes.The tangential resistance to the AFM probe was related to the scale surface adhesion,the scale surface micro-convex’ inclination,and the normal load F.In this study,the frictional properties of serpentine scales in various situations were examined.Using a friction and wear testing machine,friction tests were conducted on the abdominal scales of a red-chain snake with a typical micro-convex body structure in multiple environments by varying the contact surface roughness,humidity,and other environmental factors,and the surface morphology of the worn scales was observed by SEM in order to determine the variation pattern of the friction properties of the ventral scales with the external environment.The results of the multi-environment friction test revealed that the plowing action of abrasive grains on the ventral scale from the rough surface,the adhesion action,and the internal wear action of the scale caused by the elastic-plastic deformation were the primary causes of the tangential resistance,and that the wear produced by the scale surface consisted primarily of abrasive wear,adhesive wear,and fatigue wear.The scales had a certain frictional adaptability to varying roughness of mating pairs under varying frictional conditions and can generate relevant response modes to accommodate frictional contact in a variety of situations.In addition,the peculiar micro-convex surface shape of ventral scales can minimize scale wear.In this study,we investigated the frictional properties of the bionic non-smooth surface.The microstructural characteristics of the snake ventral scale surface are simplified,the key characteristics of the micro-convex structure are extracted,and the geometry modeling of bionic non-smooth surface is created and constructed.With the aid of software for finite element analysis,the frictional mechanical properties of the non-smooth surfaces were simulated and studied.On the cast iron sample,the nonsmooth surface was machined using a laser processing device,and the friction wear test was performed on the bionic surface using a friction wear testing machine to determine the friction wear performance of the bionic surface.In the friction wear test of the cast iron sample,the results indicate that the surface wear was primarily caused by adhesive wear,three-body wear,and rough peak abrasive wear,and that the groove structure of the weave surface had the functions of chip removal and heat dissipation,thereby reducing the adhesive wear and three-body wear.