Research On Impact Resistant Biomimetic Structure Of Spacecraft With Enhanced Toughness And Variable Stiffness

Spacecraft structure will be affected by different types of impact load in the process of lanching,satellite-rocket separation and solar wing structure deployment,which will bring great threat to the safety of spacecraft and have a negative impact on the completion of space missions.Therefore,it is very urgent to study the methods and techniques of spacecraft structure shock resistance.Considering the strict restriction of weight,volume and power consumption of spacecraft,the impact resistant methods and approaches of spacecraft structure with biomimetic conceptions are studied in this dissertation.The bone is a natural structure mainly composed of collagen fiber,hydroxyapatite and water.After natural selection and evolution,the bone components,which are not outstanding in mechanical properties,have optimized the composition and distribution and formed a unique microstructure.This makes the bone have excellent strength,stiffness,toughness and impact resistance.These characteristics provide a key inspiration for the development of impact resistant biomimetic structure of spacecraft.In this dissertation,the micro-morphology of the goat cortical bone was analyzed,and the strengthening and toughening mechanism of the microstructure of the cortical bone was revealed.Based on this mechanism,a biomimetic “biphasic” structure with enhanced toughness and variable stiffness is proposed.The constitutive model of this biomimetic “biphasic” structure is established,and the static and dynamic characteristics of the structure are analyzed.Especially,the resistance property of the biomimetic structure under typical spacecraft impacting load was studied,by taking the service environment of the supporting structure of the satellite-rocket adapter as an example.The testing samples of the two-dimensional and three-dimensional biomimetic “biphasic”structures are designed and manufactured,to verify the proposed design principles,the theoretical models and the mechanical properties of the biomimetic biphasic structure.The main work and conclusions of this dissertation can be summarized as follows:1.The microstructure of the cortical bone was analyzed,and three kinds of typical cotical bone characteristic structures were extracted,and the internal relationship between the characteristic structure of cortical bone and its strength and toughness mechanism were revealed.(1)The observation specimens of cortical bone from goat tibia were prepared,and uniform in-plane load was applied to the specimens.Scanning electron microscopy(SEM)was used to observe the microstructures in different regions of the cortical bone from 100μm to submicron.By analyzing the generation and growth of microcracks before and after loading,the strength and toughness of cortical bone in different regions and the influence of different cortical bone microstructures on its mechanical properties were revealed.(2)Based on the unique cortical bone microstructures,related to its strengthening and toughening mechanism,three kinds of cortical bone characteristic structures,namely“characteristic structure of osteon”,“characteristic structure of layered lamellae” and“characteristic structure of sacrificial bonds”,are simplified and extracted.Through the combination of constitutive equation derivation and finite element modeling(FEM)analysis,the excellent mechanical properties of three kinds of cortical bone characteristic structures in strength,stiffness and toughness are proved,which provides clear and intuitive bio-targets for the bionic composite structures.2.A new biomimetic composite structure with "enhanced structure toughness and variable stiffness" is proposed.The constitutive models of this composite structure in "0 phase" and "1 phase" are derived,and the static characteristics of the structure before and after phase changing are compared and analyzed.(1)Three kinds of “cortical bone characteristic structures” are organically combined,and a “biomimetic biphasic structure design method with enhanced toughness and variable stiffness” is proposed.A two-dimensional biomimetic “biphasic” structure is designed.The “0 phase” and “1 Phase” of the structure are defined by the “preset fracture”state of the specific area in the structure.Based on shear-lag theory,the constitutive model of two-dimensional biomimetic biphase structure in different phase states is established,and its mechanical properties such as strength,stiffness and toughness are analyzed theoretically(2)The “0 phase” and “1 Phase” of the new biomimetic composite structure are defined according to the preset damage and fracture states of the sacrificial part.Based on the composite shear-lag theory,the constitutive models of different phase states are established,and the static mechanical properties such as strength,stiffness and structural toughness are analyzed theoretically.The FEM model of the new biomimetic composite structure is established by using cohesive modeling method.Through the quasi-static numerical analysis,the theoretical derivation of the constitutive model and the simulation results are compared and verified.3.A three-dimensional impact resistant biomimetic "biphasic" rod structure is proposed,and its FEM dynamic model is established.The dynamic response and energy balance analysis of the biomimetic "biphasic" rod structure subjected to impact load are carried out.(1)The biomimetic “biphase” composite structure design is extended to a threedimensional rod sturcture.The influence of structural parameters on the equivalent viscous dissipation characteristics of the biomimetic “biphasic” rod is theoretically analyzed.(2)The FEM dynamic model of biomimetic rod is established.In particular,the dynamic response and energy balance characteristics of the biomimetic “biphase” rod during phase changing are simulated under the typical impact load of the launching process of the rocket.4.The two-dimensional and three-dimensional testing samples of the impact resistant biomimetic "biphasic" structure were designed and maunfactured,and the mechanical properties of the biomimetic "biphasic" structure were tested and studied.(1)Baded on the proposed designing principle of the “toughness enhancing,stiffness variable and impact restant” biomimetic “biphasic” structure,the testing samples of the two-dimensional “biphasic” plates and the three-dimensional “biphasic” rods were designed and manufactured.(2)The quasi-static axial pulling to failure tests were carried out for the two kinds of samples.The results show that the two kinds of samples show obvious phase chaning behavior before their respective failure,and the stiffness reduction effect is obvious during the test;at the same time,compared with the respective control samples,the test samples have the characteristics of strength and toughness enhancement.The experimental results are basically consistent with the derived constitutive equation and FEM simulation results,which further verified the design principle and constitutive model.