The Research On Hierarchicalstructure Mechanical Behavior And Biomemtics Of Fish Scales

Teleost fish(such as Grass carp,Cyprinus carpio,Crucian carp,etc.)scales are characterized by ultra-light and ultra-thin properties,of which the mechanical properties are presented as excellent flexibility and anti-puncture ability.Similar to other biological materials such as teeth and mantis shrimp,the superior mechanical properties of fish scales are related to their structure.The structure of fish scales is a hierarchical structure,which shows a unique functional gradient mechanical property.Fish scales are overlapped with each other to effectively disperse the teeth.In this paper,the morphology,structure and mechanical properties of grass carp scales were systematically studied.The mechanical properties of nine types of scales from different waters in New Zealand were analyzed and compared,thus to provide the theoretical basis for bionic design.A new type of flexible protection equipment was established by learning from the structure and overlapping mode of scales;and two new functionally gradient models were founded by learning from structures of biomaterials.The relevant research and results are as follows:(1).In order to reveal the relationship between morphology,structure and function of grass carp scales,the surface morphology and hierarchical structure of the grass carp scales were observed at first.Secondly,the uniaxial tensile tests were carried out for different positions of the hydrated and dehydrated grass carp scales,and the effect of strain rate on the mechanical properties of the hydrated grass carp scale was considered.And then,the biaxial tensile test was also conducted,and the full filed strain of the scale was analyzed by digital image correlation technique(DIC).Lastly,the punch test of hydrated grass carp scales and dehydrated grass carp scales were conducted,and the damage type of penetrated samples was observed by optical microscope and scanning electron microscope(SEM).The results showed that the grass carp scale consisted of two layers of material:the hard and outer bony layer and the soft and inner collagen layer.The collagen layer was composed of collagen fibers patterns,and the spiral angle of adjacent collagen fiber pattern dis about 28-31°.For hydrated grass carp scale,the whole scale showed anisotropy in-plane,while the collagen layer showed isotropy in-plane.The left side and right side of the scale specimen formed multiple cracks during the testing,which was related to the surface stripe coinciding with the tensile direction.The Young's modulus and tensile strength of the dehydrate grass carp scale are larger than those of the hydrated grass carp scale,but lower failure strain.What,s more,for the hydrated grass carp scale,the tensile strength,Young's modulus and fracture toughness were agree with strain rate equation,that is Ramberg-Osgood equation.The correlation of strain rate of grass carp scales was mainly related to collagen fibers layer and higher water content.The strain rate correlation of grass carp scales was mainly related to collagen layer and higher water content.According to the analysis of full field strain,we can see that the strain on the four sides of the scale is bigger than the center position.The results of the punch test show that the smaller the needle size is,the easier it is to puncture the scale,and the large size of the needle makes the substrate produce large deformation.But the peak value of the punching force is independent of the base stiffness.The effect of different sizes of punctures and different stiffness matrix on the puncture force(deformation)can provide a good reference for the design of the protective structure with low puncture damage.Through the observation and analysis of the failure mode of the punctured specimen,the hydrated scale is mainly subjected to radial tensile failure,while the dehydrated scale is mainly subjected to shear failure.(2).Tests were carried out on morphology,hierarchical structure and mechanical properties of 9 different scales taken from different waters(freshwater,shallow sea and deep sea)in New Zealand.By comparison,we can see that the left,right and posterior area of the nine different scales in New Zealand are similar to those of the grass carp scales.In addition,the composite of these nine scales,similar to the grass carp scales,both composited by the hard bone layer and collagen layer,which composed of collagen fiber panel.But the spiral angles of collagen panel of different scale are different.What's more,there are differences in mechanical properties,and the Lutjanus rivulatus scales perform the best extensibility.(3).Inpsired by fish scales and overlapping patterns of different biological materials(scales,pangolins,etc.),a biosinpred flexible protective equipment was put forward.According to the NIJ-?-level standards in United States,the limit velocity of bullet is 856.1 m/s,the optimal simulation of single biomimetic composite "scales" was studiedby LS-DYNA software,and theequivalent thickness ratio of scale was determinted by simulation.Based on the analysis of the composite"scales",the optizimation of overlapping ratio of the entire protective equipmentwas simulated.The numerical simulation results suggested that the bullet against performance is best when the thickness of scale is h=14 mm,the thickness ratio h1/h2-1 and the scale radius is 89 mm.Based on the analysis of the influence of the overlapping ratio of the scales on the protection performance,considering the protection performance as well as the equivalent area density,we suggested that ?1=80° is the best overlapping angle.The absorption mechanism of the entire protective equipment as follows:Firstlt,the outer silicon carbide layer,with a higher hardness,can absorb most of the energy of bullet,while Ultra High Molecular Weight Polyethylene(UHMWPE)produced plastic deformation to absorbe the energy of bullet,and transfer the stress to others adjacent scales,which can disppate residual energy.Kevlar layer can make the relative slip between the scales andcan be transferred part of the energy of the bullet.On the other hand,the scales are inclined,in the process of penetration,bullet will happen slip and rotaion,so that redirect the kinetic energy distribution of impact,thereby reducing the erode energy.(4).The functional gradient model was established by using different functional gradients of fish scales,teeth and mantis shrimp.Apply these models to the design of functionally graded plate,the dynamic characteristics(modal and buckling factor)are analyzed by the combination of shear discrete gap technique and finite element/extended finite element method to obtain the optimal function gradient model.The simulation results show that the traditional gradient model can change the stiffness and stability of the plate by changing parameters.For the gradient model of imitation fish scales,can be used for flexible structural design.For the gradient model of mantis forefoot,the rigidity and stability of the plate can be improved by changing the parameters,and the stiffness and stability of the plate can be reduced.Therefore,the model can be used in the design of protective structures,and can be used for flexible structural design.Therefore,the use of imitation fish scales,teeth and imitation mantis shrimp two gradient design,well the existing functional gradient material design deficiencies.