Comparative Biomimetic Research On Erosion Resistance Of Scorpions Cuticle In Different Habitats

As one of the three major failure modes of mechanical components,wear has caused serious economic,energy loss and material waste.Erosion wear is an important branch in the domain of wear.It has been recognized as one of the important reasons for the failure of equipment in various engineering products,including steam turbines,pipelines,centrifugal compressors,centrifugal fans,cyclone separators,gas drilling drill pipes,throttle manifolds,radomes,helicopter rotors,etc.At present,attempts,such as selecting wear-resistant materials,adopting surface strengthening technique or heat treatment technology,have been made to enhance the anti-erosion performance of material surface.However,these methods have not achieved a desirable effect.Therefore,seeking new anti-erosion technologies has been becoming a hot and difficult area of materials research.Inspired by nature,Parabuthus transvaalicus,a scorpion found in deserts,shrubs and semi-arid areas,was chosen as biological prototype.An Asian rainforest scorpion,Heterometrus petersii was adopted as a comparative object.Difference analysis on habitats of the two scorpions was conducted.Based on microscopic characterization means,the surface morphology and structure of the animals were compared from four levels.It was found that the terga of the scorpions are connected through intersegmental membranes,which forms natural grooves on the cuticle.In terms of the width of the grooves,the P.transvaalicus' is larger than that of the H.petersii.Compared with the rainforest specie,the cuticle of the P.transvaalicus is distributed with regional convex hulls whose particle size is larger,and the lateral region is the most intensive part.Between the convex hulls,the semi-desert scorpion is also covered with micron regular hexagonal pits.Comparing the thickness of terga,it was found that the thickness of the semi-desert specie is much larger than that of the other kind,and the thickness of the former changes obviously with the position of the curved terga.In addition,both of the two species are hierarchical composites in which the exocuticle consist of Bouligand structure,which is arranged by microfibers with their orientations varying between sheets.The honeycomb micropores on the endocuticle also enhance the compliance of the terga.The differences in the cross-section of the two scorpion' terga are mainly focussed on the thickness of the layers.As the erosion wear performance is closely related to the properties of the material itself,the chemical composition,the macro-,and micro-mechanical properties of the two scorpions' terga were studied.The results show that the distribution of Fe is consistent with that of proteins in different parts of P.transvaalicus,while the H.petersii is almost free of Fe and the protein has no significant distribution characteristic.Moreover,the elastic modulus of the former is higher than that of the latter.In the arc direction of the terga' cross-section,the lateral region of the P.transvaalicus' terga possesses the highest micro hardness,elastic modulus and H3/E2 value,and that of the edge region are the lowest.The mechanical parameters of the H.petersii' terga are only random fluctuation values.For the two animals,the micro hardness and elastic modulus of the terga exhibit a gradual decrease trend from the epicuticle to the endocuticle.For the P.transvaalicus terga' cross-section,the nano-mechanical properties of the convex hulls are significantly better than that of the non-convex hulls.A comparative erosive wear research of the living scorpions and common glass was conducted by an erosion wear equipment for small organisms.The result shows that the cuticle of P.transvaalicus possesses the most excellent erosion resistance.Then,multiple anti-erosion mechanisms of the semi-desert specie were analyzed from the surface morphologies and structures,the internal soft and hard gradient hierarchical structure,the chemical compositions and mechanical properties angles.It was found that the V-shaped grooves,the convex hulls and the hexagonal pits constitute an omnidirectional defense for the scorpion cuticle.The gradient hierarchical structure does not only avoid the body from being worn through,but also absorbs the impact energy of the particles.The P.transvaalicus cuticle was endowed with excellent erosion resistance through strengthening the mechanical properties of the terga further,which are attributed to the cross-linking of protein and Fe.Besides,the adaptation to wind-sand environment results in the lateral region of the P.transvaalicus gradually evolves thicker cuticle and denser surface morphologies.Eight kinds of bionic samples with composite structures,i.e.,V,VC,VH200,VH500,VCH200,VCH300 and VCH500 were established on the basis of the morphologies and structures of the P.transvaalicus cuticle,the machining accuracy was also taken into account.For the sake of comparative analysis,a smooth sample with the same size was designed.The nine kinds of samples were processed on EOSINT M280 laser sintering system,and EOS Stainless Steel GP1 metal powder was used as the printing material.Subsequently,a postprocessing of the samples were accomplished through wire-cutting,grinding and sandblasting machines.The erosion test was conducted with a self-made jet erosion system.The results show that the composite structures contribute to the erosion wear performance of the samples,and the V-shaped grooves have the greatest effect on the result,the effect of the convex hulls are weaker,and the hexagonal pits are minimal.Compared with smooth samples,the erosion resistance of VCH500 samples increase by about 31.9%.