Study On Tensile Wrinkle And Crack Propagation Characteristics Of Hierarchical Thin Plate Structure

Thin plate structure is widely used in aerospace field,but the thin plate structure often fails due to wrinkle or crack propagation during its service,and even has safety problems.when the sheet structure is subjected to compressive stress,it is easy to lose stability to produce wrinkles.for the aerospace field with high precision requirements,wrinkles mean the failure of the structure the thin plate is also prone to produce microcracks during long service.under the action of external loads,cracks will be more easily extended to produce fractures and even cause safety problems.So it is of great significance to study wrinkles and suppression of crack propagation.Firstly,the paper studies the process of wrinkle formation of film structure under tensile load.The model of the film subjected to uniaxial tension is established,and the instability process and the final form of fold are investigated by finite element simulation.The effect of drilling holes in different positions of the film on the wrinkles of the film structure was also investigated.Punching can be considered as weakening the partial stiffness of the film structure,and the effect of increasing the partial stiffness on the film wrinkle is analyzed.Combining the above two methods,the model of variable stiffness structure is proposed,and in the film / substrate structure,the effect on the film wrinkle is observed by changing the stiffness of the substrate.Secondly,with reference to the hierarchical structure of organisms such as shells,the influence of the layered thin plate structure under uniaxial tensile loading on the wrinkle is investigated.a hierarchical thin plate structure without prefabricated cracks is established and divided into 32 blocks of regions,each of which randomly distributes different units(three types of units designed above).the final form of the fold is observed by finite element simulation and classified according to the different forms of the wrinkle.The model has a large sample space,so machine learning is used to explore the effect of different cell distribution on wrinkle,and the classification law of the effect of this hierarchical structure on wrinkle is obtained and verified.on this basis,the definition of confusion degree is proposed to describe the distribution of materials,and the law between confusion degree and wrinkle distribution is explored by machine learning,and verified.finally,the feasibility of the above two classification methods is evaluated within the range of error allowed.Finally,the variable stiffness structure proposed in the previous chapter is designed,and the influence of variable stiffness on the suppression of crack propagation in thin plate structure is explored.The stiffness ratio of two suitable materials is 100:1,and three different cell models are designed to change the distribution of the two materials,and the relevant parameters of the three cell structures are obtained by finite element simulation.then a hierarchical thin plate model with prefabricated cracks was established and divided into 64 regions,each of which randomly distributed different units(three types of units designed above).To investigate the influence of different cell distributions on the crack propagation inhibition of thin plate structure.The effective strength and toughness are defined for the non-uniform materials,and the effect of different structures on crack propagation is determined.the model has a very large sample space,so the influence of different cell distributions on the suppression of crack propagation is explored by machine learning.finally,a better structure than the existing samples is optimized.the structure has higher effective strength and effective toughness,that is,a variable stiffness distribution structure that can better suppress crack propagation is optimized.