Biological Coupling And Bionic Anti-wear Properties Of Typical Molluscan Shells

Abrasion could be described as a process of wearing down or rubbing away by means offriction between the contact bodies during relative motion. Abrasion exists extensively inengineering field, and causes serious material and equipment failure. According to thestatistics, the failure of80%of mechanical parts or more is due to wear and tear, and30-50%of global energy consumption is attributed to friction and abrasion. Abrasion not onlyconsumes material, but also wastes energy, and directly affects the life and reliability ofmechanical parts. Thus, the abrasion becomes a problem to be urgently conquered nowadays,and perhaps such solutions could be learned from the nature. Biological creatures live inharmony with nature upon the combination of multiple factors, e.g. surface morphologies,complex structures and component materials, and achieve the optimum adaptation to thesurroundings based on such biological coupling functions. So in the current study, threetypical molluscan shells Scapharca subcrenata, Rapana venosa and Acanthochitonrubrolineatus were selected to study their biological coupling and bionic anti-wear properties.The paper tries to provide reference information for the development of innovated anti-wearcomponents as well as for the complement of the coupling bionic theory.Molluscan shells are fascinating examples of highly ordered hierarchical structure andcomplex organic-inorganic biocomposite material. The selected shells S. subcrenata, R.venosa, and A. rubrolineatus are typical molluscan species respectively belonging toimmersed, demersal crawling and attached crawling life forms, and involving the threerepresentative species of mollusca including Bivalvia, Gastropoda and Polyplacophora. Theseshells have specific living behaviors and exhibit exceptional wear resistant properties. In thispaper, more experimental methods were applied to study their biological, mechanical andwearing properties. And the large finite element analysis software ANSYS was further usedto simulate the abrasive and erosive process of the built uni-bionic models and thedual-bionic coupled models. The biological coupling and bionic anti-wear properties of thesethree typical molluscan shells thus were preliminarily revealed in this paper. During the biological coupling analysis, the stereomicroscope, SEM and X-ray diffractionwere respectively used to investigate the surface morphologies, microstructures and phasecompositions of the shells. Observations showed that the surface morphology of the left shellof S. subcrenata is much complicated distributed with radial riblets coupled with nodules.The crossed lamellar structure was found generally existing in the three shells displayedhighly ordered hierarchical structure. In S. subcrenata and A. rubrolineatus, the specificwell-developed pore canal tubules were also discovered. According to the phase components,aragonite is the most extensive phase present in the molluscan shells, which could effectivelyresist the external damage. Micro-Vikers hardness test demonstrated that the micro-hardnessof each layer closely relates to its corresponding microstructures and shows anisotropy. Thecrossed lamellar structure in the sub-layer of S. subcrenata and the nacre layer of R. venosashowed the highest micro-hardness, and the similar structure in the chiton also displayedrelatively high micro-hardness. Compressive test indicated that the bearing capacity of thelayered section of the shells is higher than that of the transverse section. The compressivestrength of the shell also corresponds to its microstructures.In the abrasion test, the methods of separate testing and selective removing of the individualcoupling element were used to respectively investigate the effects of coupling elements e.g.morphology, structure and material on the abrasive properties of the shells of S. subcrenataand R. venosa by the rotary-disk type abrasive wear tester. Through comparative analysis, theimportance degree of different coupling elements during the abrasive process of the shell of S.subcrenata was revealed, that is the organic material could be classified as the main couplingelement, riblet morphology could be considered as the hypo-main coupling element, and thecomplicated structure composed with riblets and nodules could be regarded as the normalcoupling element. The wear-resistant mechanisms of each coupling element were alsoanalyzed. At the same time, the abrasion anisotropies of the shells of S. subcrenata and R.venosa were studied and analyzed. The experimental results demonstrated that the wearresistant property of the shell of S. subcrenata is the best, while that of the R. venosa isrelatively not prominent. The tentative erosion test preliminarily indicated that the bodysurface of the chiton exhibits strong erosion-resisting merits. The relationship between thestructure and the function of the three shells were also explored in this paper. According to the biological coupling anti-wear property of the shell of S. subcrenata, thesurface morphology uni-bionic model, the morphology-structure and themorphology-material dual-bionic coupled models were independently constructed, and thecomputational fluid dynamic software ANSYS/CFX was applied to simulate the abrasiveprocess of the models. The simulation results showed that the anti-cutting and anti-erosionproperty of the morphology-structure coupled model was generally better than that of themorphology uni-bionic model. It means that the complicated structure composed with ribletsand nodules could effectively decrease the velocity and the forces of the fluid, weaken thewall shear stress of the model, and in final reduce the contact stresses of the solid domain.The morphology-material coupled model probably underwent deformation during theabrasion process and caused the incorrect result of one-way coupling simulation. Theabrasion mechanism and the model optimization were further proposed in the paper.The explicit dynamic software ANSYS/LS-DYNA was used to simulate the erosive processof the configuration uni-bionic model and configuration-groove/convex morphologydual-bionic coupled model imitating the shell surface of chition. The mechanism of erosionof each model was comparatively analyzed. The overall erosion resistance of the threemodels was sorted as convex-curved plate, groove-curved plate and smooth-curved plate.However, in the peak of the curved plate, the stress dispersion effect of groove is much betterthan that of convex, whereas the stress dispersion effect of convex is better than that ofgroove at the pterion region. The simulation results indicated that the shell plate of chitonevolved an optimum combination of morphologies with thick riblets distributed in the peak(grooves are thus formed between the riblets) and convexes scattered around the pterionregion, and thus endow the chition with exceptional wear resistance.The study on biological coupling anti-wear properties of typical molluscan shells furtherproved that coupling bionics is more nearly to the real function mechanism of the biologicalcreatures and thus produce better efficiency. Therefore, the further study on coupling bionicswould greatly promote the process from similar in appearance to similar in spirit andundoubtedly would be of great theoretical value and practical significance.