| Wild oats is a common farmland weed.Its mature seeds have a brown knee-shaped needle awn,which can three-dimensional rotational deformation motion with the change of environmental humidity,which can help the attachment the cone is drilled into the crevices of the soil to spread the seeds.Exploring the microstructure,movement characteristics and the principle of moisture absorption and deformation of wild oats wheat awn cells has an important enlightening effect on the design and preparation of bionic self-driving intelligent devices.In this study,the basic principles and mechanical properties of the hygroscopic movement of the wild oats were studied in detail,and on this basis,the bionic wheat awn fiber cells model were designed and prepared.The specific research content and results are as follows:(1)With the help of scanning electron microscope and focused ion beam scanning electron microscope,systematically observed the morphology structure of wild oat awns from a microscopic point of view,determined the hygroscopic awn fiber arrangement and layered structure form.Subsequently,we measure the mechanical properties of the different bundles fiber cells of wild oats by tensile tests,and the quantitative relationship between the mechanical properties and moisture content of a single wild oats cell and its hydrophilic matrix are analyzed based on the test results and material mechanics theory.The results show that the mechanical properties decrease with the increase of water content;within the range of the measured water content,the maximum elastic modulus of wheat awn cells is 12.78GPa,and the minimum is 8.11 GPa;the maximum modulus of the hydrophilic mixed matrix is 8GPa,the minimum value is 0.054GPa.(2)Based on the analysis of the microstructure and mechanical properties of the wild oat cell,we establish finite element model of the thick-walled composite spiral tube corresponding to the size and performance of the biological prototype.By applying humidity load,the deformation forms and deformation results of the finite element models of single and multiple fiber cells are obtained.The results show that the finite element model would generates rotation deformation under the action of humidity load;when the water absorption concentration changes is most,the axial strain of the single fiber and the second,third,fourth,and seventh fiber bundle models respectively are 30.794%,30.869%,31.114%,31.356%,and 30.842%,and at this time the torsion angles per unit length respectively are 8.21×10-3rad/?m,8.92×10-3rad/?m,9.13×10-3rad/?m,9.73×10-3rad/?m,8.59×10-3rad/?m.(3)Through a comprehensive investigation of smart material preparation technology,synthesis efficiency,response rate,mechanical strength,etc.,semi-IPN smart hydrogel is selected as a hydrophilic matrix bionic substrate,and explore the swelling and deswelling of the hydrogel substrate.At the same time,the effect of water content on the mechanical properties and volumetric strain of the gel is also characterized.The results show that the smart hydrogel has a faster swelling and deswelling rate;with the increase of water content,the elasticity of the gel becomes larger and larger,but the strength becomes smaller and smaller;the volumetric strain when the hydrogel absorbs water in equilibrium reaches 9.781%.(4)On the basis of elucidating the structural characteristics and deformation principle of the wild oat awn cells,using the selected flexible hydrogel matrix and high modulus fibers as the bionic substrate,a bionic wild awn awn single fiber and bundle fiber cell model are designed and prepared.The model found that they can rotate deform spontaneously when they meet with water.And through experiments to explore the response rate of these bionic cell models and the influence of water content on their deformation variables.The results showed that when the number of fiber cell models increased from one to five,their moisture-absorption rotational deformation rates are 0.055 rad/min,0.112 rad/min,0.146 rad/min,0.163 rad/min,and 0.173 rad/min,respectively;at moisture absorption balance the torsion angles are2.583 rad,5.585 rad,6.719 rad,7.592 rad,8.290 rad. |
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