Study On The Relationship Between Structure And Mechanical Behavior Of Sea Urchin Shell By Finite Element Analysis And Experimental Verification

The application of bionic principles to design new materials and engineering structures is a hot topic in recent years.The rich marine biological resources of the South China Sea provide endless materials for structural bionics.Sea urchins can live in the intertidal zone with heavy waves to the seabed of several kilometers,and their shells(or tests)have evolved excellent mechanical properties to withstand the hydrostatic pressure and wave impact.As a lightweight and porous multi-plate composite shell,the relationships between its unique structure and its mechanical behavior may have great guiding significance for the design of new materials and engineering.In this paper,the common Anthocidaris crassispina(a sea urchin)in the South ChinaSea was selected as the main research object.The sea urchin shell(terminology:Sea Urchin Test;abbreviation:SUT)was divided into six levels from macroscopic to microscopic from the perspective of inorganic skeletal hierarchical structure:whole test,ambulacrum,test plate,porous body(stereom),trabecula,and crystal plate.Using digital cameras,polarized light microscopy,scanning electron microscopy(SEM)and other characterization instruments,as well as image analysis and mathematical software,the geometrical features of the SUT structure were mathematically analyzed to lay the foundation for the construction of the SUT structure model.The relationship between SUT structure and its mechanical behavior was analyzed in depth by finite element method(FEM)and bionic simulation experiment.The main research works and conclusions are as follows:(1)The effects of three different scales of organic-inorganic composite structures(cuticle-test plate,stroma-stereo,IOM(Intrastereomic Organic Matrix)-crystal plate)on the mechanical properties of test plates were analyzed by gradual removal of organic matter.The results show that after 300? pyrolysis of IOM,the flexural performance of the test plate is reduced by 55%,while the damage of the other two organic structures has little effect.The optimal aspect ratio and curvature of the IOM-crystal plate assembly(trabecula)were calculated by FEM.The results show that the calculation results are basically consistent with the measurement results of the inner surface of the SUT.The curvature radius of trabecula wall:trabecula length:trabecula diameter is 2:2:1.(2)It is found through microstructural characterization that the stereom composed of trabeculae presents a three-layer distribution of GSR(Growth Layer,Support Layer,and Resorption Layer)from the outside to the inside of the shell.After transforming the porous three-layer structure into a three-layer elastic modulus model,the mechanical simulation experiment was used to analyze the failure behavior of SUT under hydrostatic pressure,bite force and self-weight moreover,the effect of GSR and other sequences structure on the mechanical behavior of SUTs were studied by FEM.Results show that the SUT with GSR structure has the best comprehensive mechanical behavior in these models to resist environmental destructive forces.(3)Through structural characterization,it is found that a large number of mineral bridges are discovered between the test plates composed of the stereom and the ambulacra composed of the test plates.The mechanical effects of mineral bridges on SUT were analyzed by mechanical experiments and FEM.The results show that the mineral bridge can strengthen the joint of test plates,and the joint strength increases with the increase of mineral bridge distribution density.The mineral bridge was formed in the grain boundary of alumina ceramics by crystallization control method,and the strength and toughness of ceramics were increased by 33.97%and 33.52%,respectively.(4)The effects of tube foot pore position on the mechanical behavior of SUTs were studied by FEM and simulation experiments.The results show that the presence of the tube foot pore in the part position of the SUT can increase the mechanical behavior of the shell under hydrostatic pressure and/or unidimensional bite force.This paper not only provides a theoretical basis for bionic material and engineering design of SUT structures,but also provides new methods and ideas for structural analysis of other biological shells.