Topological Optimization Design Of Civil Aircraft Structural Components With Fatigue Constraint Determined By DFR Method

Aircraft structure lightweight has always been the ultimate goal in the field of civil aircraft.Research shows that every 1 % reduction in aircraft weight will improve aircraft performance by 3%.Topology optimization design is the most effective way to reduce civil aircraft weight.In the past,structural topology optimization only considered stiffness constraints,and only verified the static strength of the optimized components.However,the main failure form of load-bearing structures in the field of civil aircraft is fatigue failure,so it is necessary to propose a topology optimization method that can improve the fatigue resistance of components.The topology results are usually prepared by additive manufacturing technology,and the initial topology components will have isolated bodies,broken branches and other features that affect the preparation,so how to deal with these features should be considered to improve the manufacturability of the topology.In this paper,the goose neck chain,a typical metal sub load bearing civil aircraft component,is taken as the research object,and systematic research is carried out around the topology optimization design of additive manufacturing parts considering fatigue,mainly including the following parts:(1)A topology optimization method based on fatigue constraints is proposed.By comparing and summarizing different fatigue life analysis methods,the stress,the most representative influencing factor in fatigue life,is put forward,which provides theoretical basis for transforming fatigue constraints in topology optimization into stress constraints.Based on the variable density topology optimization method,the mathematical model of topology optimization with stress constraints is established.Finally,the influence degree of stress value on fatigue life is analyzed,and the traditional method of material yield stress restraint is discarded.A detailed fatigue rating(DFR-Detail Fatigue Rating)method is selected to confirm the restraining stress,which is more representative of stress in dangerous parts of components.(2)Topology optimization analysis based on DFR method.In order to maximize the material properties,a detailed fatigue rating analysis method is used to select specific calculation formulas and confirm the correction parameters according to the structural and operating characteristics of goose neck chain.The allowable value of DFR is 292 Mpa,which is the stress constraint value in the process of topological optimization.In order to establish a reliable finite element model,before the optimization analysis,the tensile and finite element analysis contrast experiments are carried out on the original members,and the most reliable material property parameters are selected to establish a reliable model by comparing the finite element results and experimental data.The secondary development of commercial software ABAQUS is used to solve the topological optimization of original goose neck chain with stress as constraint and minimum volume as objective function,which provides the initial topological configuration for subsequent preparation and verification of fatigue.(3)Topological configuration post-processing and fatigue resistance verification.According to the characteristics of the initial topology optimization structure,such as isolated bodies and broken branches,which affect the preparation of additive technology,the rules for geometric reconstruction of topology structure are proposed,and the reconstruction post-processing is carried out according to the reconstruction requirements and characteristics of gooseneck chain;With the help of commercial software Inspire,the configuration before and after reconstruction is verified by finite element simulation of additive manufacturing,which proves that the reconstructed components meet the requirements of additive manufacturing;Then use the commercial software ABAQUS to carry out static finite element simulation for the reconstructed configuration and the initial configuration.Based on the simulation results,use the professional fatigue analysis software Fe safe for joint simulation.The final simulation results show that the maximum weight reduction ratio of the configuration after removing the isolated body and broken support features is 46.93%,but its fatigue life is 20371 times.Although the weight reduction ratio of the component connecting the isolated body and broken support features is the lowest 45.3%,its fatigue life is the largest 23067 times.