Research On Bio-inspired Flexible Strain Sensor With Adaptable Properties For Spacecraft Under Extreme Conditions

Research on bio-inspired flexible strain sensor with adaptable properties for spacecraft under extreme conditionsThe design and development of spacecraft with high intelligence and high performance has been regarded as an important cornerstone for China to move from ’major player in space ’ to ’ aerospace power’.With the rapid development of engineering science in China and the advancement of a series of strategic measures,spacecraft is undertaking more and more on-orbit tasks,resulting in more complex structure.Meanwhile,the spacecraft is easily disturbed by its own structure and external environmental factors during long-term in-orbit service,which causes mechanical vibration and structural deformations.Such deformations and vibration will not only affect the working performance of its design,but also affect the operation accuracy of the spacecraft.Seriously,it will cause damage to the main structure of the spacecraft,and even lead to the failure of the aerospace mission.Therefore,the real-time monitoring of the deformation state of the spacecraft structure provides reliable information for the intelligent identification of the spacecraft structure in orbit,which offers effective technical support for ensuring the safety and reliability of the overall structure of the spacecraft,improving the working accuracy of the spacecraft and reducing the cost of structural maintenance.However,the complex structure design and extreme working environment of spacecraft make strict requirements on the design of flexible sensors: excellent sensing performance and strong environmental adaptability,which is difficult to make a breakthrough in the short term only by traditional materials and structure design.Thus,it is urgent to solve the bottleneck of the development of the above flexible sensing elements,break through the limitations of traditional structure and material design,and seek a new direction for the performance optimization and environmental applicability improvement of flexible strain sensors.Billions of years of extremely stringent tests,scorpion has learned how to use the minimum cost to pursue their own function and structure optimization,in order to achieve the perfect adaptation evolution.In order to compensate for the lack of vision,scorpion evolved sensing organs on body surfaces that were sensitive to micro-vibration signals to capture the vibrations caused by the activities of natural enemies and prey in the surrounding environment.At the same time,the footprints of scorpion,an ancient creature,can be glimpsed either in deserts or in crisis jungles,which indicates the safety and reliability of its sensing organs and makes scorpion highly adaptable to the environment.Biological unique structure and special function,has been regarded as an important source of technological invention and creation.Therefore,exploring and imitating the excellent perception function and environmental adaptability of scorpion provides a new solution and theoretical basis for the health monitoring of large-scale spacecraft on-orbit operation structure.This paper selects adult scorpion(Heterometrus petersii)as the biological model.The morphological characteristics,multi-level cross-scale structures,response process under external excitation,surface contact angle,adhesion behavior and mechanical properties of the scorpion the slit sensillum were studied by a variety of characterization methods,such as ultra-depth optical microscopy,field emission scanning electron microscopy,μ-CT,ultra-thin sections of biological tissues and so on.It is proposed that scorpions can realize sensitive sensing of external micro vibration signals by monitoring the strain at the sensing structure of the seam sensor.Combined with Cassie-Baxter model,the mechanism of self-cleaning function based on multi-scale micro-nano structure of tarsal end surface was explained.On the basis of obtaining the microstructure and material properties of the internal tissue,it is found that the multi-layer fiber structure in the thickness direction endows the silt sensillum with the load-carrying safety.Combined with the three-dimensional reconstruction model of X-ray scanning,the unloading effect of circular through-hole was proposed through finite element simulation analysis.The theoretical analysis was carried out based on the measurement data of mechanical property,and the stress regulation effect caused by the gradient stiffness distribution of the main body of the slit sensillum was found.These two features can effectively reduce the external load and protect the integrity of the sensing structure.Subsequently,in order to meet the stringent requirements of spacecraft hygrothermal test,the ceramic fiber paper with good thermal stability was selected as the substrate of the sensing element.The optimized sensing structure and multi-level coarse structure of the scorpion slit sensillum were introduced into the substrate surface,a high sensitivity(1254.00)bionic flexible strain sensor with high temperature resistance(220 °C)and superhydrophobic properties was developed.The basic performance and basic application characterization(voice recognition,micro-expression recognition,human joint monitoring and non-contact measurement)of the bionic flexible sensing element were completed,and the application of the sensing element in high temperature and humidity environment was preliminarily explored.Then,in view of the complex load environment of spacecraft,inspired by the super-sensitive mechanism of the sensing structure of the scorpion slit sensillum and the bearing safety mechanism of the plate-layer fiber structure,the sensitivity and safety of the biological receptor are integrated into the design of the strain sensing element,and a bionic flexible strain sensor with excellent mechanical strength is developed by combining basalt fiber with Ecoflex elastomer.Then the basic performance and basic characterization are studied,and the sensing mechanism and enhancement mechanism are analyzed.A series of experiments were designed to preliminarily explore the application of flexible sensors in wearable fields(muscle deformation monitoring,joint deformation monitoring and motion state recognition)and extreme conditions(large load,underwater environment).Finally,in order to meet the needs of large deformation measurement of spacecraft components,inspired by the gradient stiffness stress regulation mechanism of the main body of the scorpion slit sensillum and the unloading effect of the unloading hole in the internal tissue of the sensor,the anti-fracture mechanism of biological structure and material coupling was introduced into the framework of the crack-based sensing element.A bionic wide-range(Δe up to 150 %)flexible strain sensor with high sensitiuvity(1720.50)is developed by combining mechanical cutting,laser marking and semi-curing technology,and the basic performance characterization was completed.On this basis,the working mechanism and reinforcement mechanism were explained.At the same time,the potential applications in large deformation(human wrist,knee,neck and spine bending monitoring)and small deformation(microexpression recognition,motion state recognition and music recognition)fields were preliminarily explored.