Research On Relationship Between Topological Structure And Mechanical Property Of Plant Leaf

Through species competition and natural evolution for millions of years, natural organisms have formed many reasonable and perfect structures. Medium axis, as a kind of pattern phenomenon, exists widely in most living organisms. And a certain relationship between the topological structure of MA and environmental stress must exist. In this thesis, the leaves of plant have been selected as the study object. The relationship between the leaf topological structure of MA and mechanical property has been investigated through experimental and numerical methods.Six representative plants are selected. And geometry size, physical parameters and mechanical parameters of the leaves have been measured. The simplified finite element models of leaf are built based on measurement data. The maximum deformation of Aleurites molucana leaf was measured by designed experiment. Experimental result was compared with the numerical simulation result. The agreement between the two methods proved analysis by numerical simulation method is feasible and reliable.In the aspect of leaf statics, wind load in different directions was applied. The results showed that the deformation and Von Mises stress decreased obviously with the increase of wind angle. The destructive effect caused by wind load can reduce by adaptive adjustments of leaf pose. For the leaf with different thickness, different size lateral veins and midrib, the calculation results under the rain load show that the changes of midrib size have significant effect on the stress and deformation of leaf. The whole stiffness and strength of has been significantly influenced as well. In addition, leaf stress and deformation under random wind load with sensitivity to the leaf design parameter was analyzed. The results show that the effect of wind load is the biggest and critical, then Young modulus of veins, and the influence of mesophyll Young modulus is the least. The vein system of leaf has the greatest contribution on the whole stiffness and strength.In the dynamics of the leaf, the result of model analysis was calculated with the ANSYS. Its first five order natural frequency and vibration mode are obtained. The results show that the natural frequency of Roystonea regia and Chrysalidocarpus lutescens has widely value, and their first inherent frequency is relatively small so that coming about the resonance easily. Vibration mode is mainly waving. Natural frequency of other leaves is relatively concentrated, and the maximum displacement of each mode always occurs in the edge of leaf. So the leaf looks like convex. We believe leaf can reduces the wind load effect with the increased excitation frequency. Meanwhile, the calculation of different structure leaf shows that the natural frequency of the leaf increases with increasing in veins size, the change of midrib size has most significant impact on natural frequency.The topological optimization results for different leaf model show that material density function is related to load vectors, constraint condition and leaf shape. The optimized topological structure is similar to the actual veins pattern. It is further explained that the veined structure pattern gives the most contribution to the global stiffness of the leaf. The leaf topological structure has instructional significance to the self-adaptive cantilever structure design against wind load.