Study On The Impact Resistance Of Coconut And Its Bionic Structure

Nature is the inspiration source for scientific development.Over the past few decades,extensive researches about biological materials has revealed the mechanical properties of natural materials and structures.In the field of bionic design,we want to reproduce the superior structure and material properties of biological materials in artificial materials.By observing natural phenomena and restoring ecological experiments,this paper discovered the mystery of the natural structure of coconuts,by using mechanical experiments,theoretical explanations and numerical simulation methods to reveal the impact resistance of coconut natural form.And the bionic structures based on the material performance of coconuts and cross-scale structural characteristics were designed and optimized to serve engineering applications.The main research contents are as follows:(1)Based on the observed results of the free fall of coconuts,ecological experiments were restored,and the natural mysteries of coconut structure discovered.Firstly,by using the coconut fruit free fall experiments,it was observed that the bottom of the coconut structure always touched the ground first without initial velocity and initial angle.Secondly,by dissecting the coconut fruit structure and making multi-scale observations,it was found that the coconut structure has typical hierarchical structure characteristics,and it was found that the fiber has the characteristics of macro-order and micro-disorderdistribution,and the arrangement direction of the bottom fiber is close to the impact load direction of free fall,which reflects the characteristics of structural-functional adaptation.Finally,by using the single-axis quasi-static compression experiments,the failure mode and destruction mechanism of the mesocarp material in coconut were observed,and the conclusion was drawn that the structure suction energy is inversely proportional to the angle value of fiber arrangement/load direction.(2)The mechanical model of coconut structure was established,and the theoretical derivation and numerical model were carried out,and the scientific mechanism of coconut ecological structure was explained by theoretical analysis and numerical simulation.First of all,the coconut peel material is composed of the matrix material and fiber material,belongs to the natural composite material.By using the macro strength criteria of fiber-reinforced composite materials Tsai-Wu's criteria and the micro-strength criteria Hashin's criteria,respectively,the theoretical expression of the relationship between the elastic strain of fiber-reinforced composite materials and the degree of fiber arrangement angle was derived,and the scientific mechanism of the macro-orderly distribution of fiber in the natural form of coconut was explained.Secondly,the theoretical analysis results were verified by numerical simulation,and the influence law of fiber arrangement and load direction angle on the absorption performance was further proved.Finally,a simulation model of coconut fruit fall was established,and the conclusion was drawn that the stress wave propagates along the direction of the coconut mesocarp fiber in the impact process.(3)Based on the microscopic observation of the mesocarp fiber in coconut,the bionic multi-stage absorption structure with the impact-resistant property inspired by the coconut mesocarp fiber was designed,and the bionic structure was parameterized and optimized to improve its crashworthiness property.First of all,based on the experimental observations of the mesocarp fibers in coconuts,the bionic multi-stage energy absorption tube with hierarchical structure characteristics was designed.Secondly,the numerical analysis of the bionic multistage energy absorption tube under the impact load was carried out and it was found that the crashworthiness property of the bionic multi-stage energy absorption tube is superior to that of ordinary circle tube,and the scientific mechanism of its excellent energy absorption performance was explained through theoretical analysis.Finally,the structural parameters of the bionic multi-stage energy absorption tube were optimized by using experiments design method,numerical analysis method,surrogate model technique and multi-objective optimization theory,and its impact resistance was improved.(4)Based on the multi-scale observation of the coconut fruit structure,the bionic sandwich structure inspired by coconut peel was designed,and the impact resistance was simulated and the mechanism was studied,and the structure of the bionic sandwich structure was optimized to improve its impact resistance property.First of all,based on the multi-scale experimental observation results of coconut fruit structure,the bionic sandwich structure with hierarchical structure was designed,and its core layer had the disorderly arrangement characteristics of the microstructure of coconut fiber.Secondly,the numerical analysis of the core of the bionic sandwich structure under the impact load,and it was found that it has different dynamic responses at different loading velocity,and the theoretical expression of the relationship between the dynamic response of the core of the bionic sandwich structure and its material,structural parameters and load velocity were obtained.Then,the numerical analysis of the bionic sandwich structure under low-velocity local impact load was carried out,and it was found that its energy absorption performance is better than that of sandwich structure with ordinary hexagonal honeycomb core,and the theoretical expression of the relationship between the impact resistance property of bionic sandwich structure and its material,structural parameters and mass,velocity and geometric parameters of the drop hammer were derived through theoretical analysis.Finally,the structural parameters of the bionic sandwich structure were optimized to improve its impact resistance property.