Study On Mechanical Property Of Climbing Plant Tendrils And Mechanical Behavior Of Chiral Fiber Pull-out

Chiral biological material generally shows unusual properties of materials and mechanical behaviors due to its unique mechanical characteristics and structure.Towel gourd and other tendrils of climbing plants which can withstand great deformation and offer the support of helping plants capture the sunlight have geometrically spiral shapes.The biological material such as bone wood,tendon,and so on has chiral microstructure or even multi-level chiral structure on molecular,microscopic and macroscopic scale.Its unique mechanical properties mainly comes from synergistic effect of chiral microstructure at multiple levels.The chiral fibers composed of helical microstructures have significant influence on the mechanical properties of fiber biocomposite.The mechanism of how the chiral microstructure affects the performance of biocomposite is still unclear.The study of the structural-performance relationship of chiral biomaterial not only helps to deepen our understanding on growth and properties of chiral biomaterial,but also inspires us to design for constructing advanced functional materials based on chiral microstructures.This thesis focuses on a finite element model of tension of bistable helix which is created to investigate the process of deforming the tendril and the influence of chirality on the mechanical behavior.The effect of microstructure on the properties of tendril is analyzed by the tensile test of bistable helix,the microstructure observed and the simulation results.The author finds that the unique mechanical properties of the tendrils are determined mainly by the combination of the macroscopic bistable helical structure and the micro-cellulose helix structure.In addition,based on the microstructure characteristics of climbing plant and wood,a finite element model for analyzing the process of pulling out chiral fiber is established.The composite chiral fiber is formed by embedding helical filament in a elongated cylindrical fiber.The element of cohesive force is adopted in the chiral fiber-matrix interface for studying the effect of filament angle of spiral fiber and helical fiber-matrix elastic modulus ratio on the pull behavior of chiral fibers.The effect of chiral fiber on the properties of biocomposite is analyzed to utilize the force-displacement curve of the pulling process and the stress distributions at chiral fiber-matrix interface is also investigated.The finite element model for pulling chiral fiber from hyperelastic matrix is established.The effects of the hyperelastic properties of chiral fibers,the initial microfilament angle and the elastic modulus of helical filaments on the pulling behavior are investigated.Furthermore,the influence of the hyperelasticity of the matrix on the properties of the biocomposites is also studied.