Deformation Prediction And Process Optimization Methodology For Aircraft Panel Structures With Automatically Riveted Joints

Panels are the most important components of aircraft structures to ensure aircraft aerodynamic configuration,and its assembly accuracy directly affects the aerodynamic performance.The key processes and difficulties of panel automatic assembly are the planning of riveting parameters and the prediction of riveting deformation.Traditional studies are mainly concentrated on the deformation analysis of rivet itself and adjacent region of rivet hole,and the effect of riveting process on the global deformation of panel is seldom analyzed and predicted.The relationship between the riveting parameters and the deformation of the panel is also not further explored.With the development of new stealth aircraft,the requirement of assembly accuracy is improved,and the assembly precision of panel should be improved higher.However,the traditional methods have some limitations.In this paper,the panels considering the local and global deformation are taken as the object of study.Aiming to reveal the mechanism of riveting deformation,predict the riveting deformation of panel,plan the riveting parameters and assure the assembly accuracy,a series of analytical models and methods are developed,which can provide guidance for controlling the riveting deformation in typical thin-walled structure of panel.The main work of this paper is as follows:(1)A mechanical model of riveting process of the protruding head rivet is established,and the mechanical mechanism of deformation in single riveting process is revealed.According to the rivet material flow trends,the riveting process is divided into four stages,and the moment of maximum riveting force occurring could be determined.The analytical models of elastic and plastic deformation for rivets and plates are established,respectively.Based on the contact conditions between the rivet and plate,the rivet contained two parts,one is the part in the hole,and the other is in the outside of hole.Combined with the principal stress method and the geometric relation of driven head under inhomogeneous deformation situation,a calculation model of riveting force is built.Based on Hertz contact theory,the displacement distribution of rivet hole under the extrusion of driven head is solved.After the riveting force removal,the distribution of residual stress of plate is also given.By means of numerical method,the material flow is analyzed,and the distribution of deformation state in plate is discussed.The mechanical analysis of aircraft plane is accomplished during the whole riveting process.The value of riveting force is calculated exactly,and the mechanism of local riveting deformation is illustrated.(2)A theoretical prediction method of riveting deformation for long strip plate under simple boundaries is proposed.By means of the linking method of solid element and shell element,a numerical modeling method suitable for panel automatic assembly is introduced.Theoretical prediction and rapid calculation of riveting deformation are realized.In order to construct the relationship between the discrete local deformation and the global deformation of structure,the stress state around the rivet hole of single riveted and multi-riveted structure is analyzed,and the effect of rivet sequence on the stress distribution is also discussed.Combined with the simplified radial residual stress,a calculation model of local riveting deformation is established.Based on the radial residual stress homogenization assumption,a theoretical calculation model,applied to simple constraints,is built to estimate riveting deformation of strip plate.Aiming at the panels with complex boundary conditions and shapes,a numerical modeling method and procedure is proposed based on the linking method of solid element and shell element.The above models and methods demonstrated the influences between riveting circles,and types of riveting deformation,which could be used to estimate the riveting deformation of long strip plate.Using the “solid-shell” linking method,the complex stress-strain appeared around the rivet hole is transferred to the shell element in a relatively simple state by the solid element,which improves the computational efficiency.(3)A “local-global” mapping model is developed to predict riveting deformation of panel under complex boundary conditions,and the influence of boundary conditions and riveting sequences on the deformation is also studied.Due to the complicated structure of panel and expensive computational cost of riveting deformation,the characteristics of structure and the assembly process of panel are analyzed firstly.A finite element model for the calculation of the inherent deformation of the local structure is constructed.Based on the method of equivalent stiffness,the structures,which blockes grid division,are simplified.The approaches,including riveting point determination,inherent deformation loading and boundary condition definition,are proposed,which are suitable for the panel components.Combined with the “solid-shell” linking method,a “local-global” mapping model is constructed to predict global riveting deformation of panel.The effect of boundary conditions and riveting sequences on the deformation is also studied.The calculated results show that the proposed “local-global” mapping model could significantly reduce the computation time.At the same time,it is found that,when two end boundaries are fixed,the gap would be generated between the sheets,while warping phenomenon occurred when one end is a free.The jump riveting method could reduce riveting deformation.(4)A process optimization method combined Kriging-Particle Swarm Optimization(Kriging-PSO)and a path planning model based on Genetic-Ant Colony Algorithm(GA-ACA)are proposed.In order to meet the requirements of local deformation and global deformation control,the uniformity is chosen to evaluate the local riveting deformation,while the smoothness is set as the goal of global riveting deformation.An integrated method combined Kriging metamodels with particle swarm optimization(Kriging-PSO)is developed to optimize riveting parameters.Kriging surrogate models are built to reflect the mapping relationship between process parameters and the local deformation,and PSO is used to search for Pareto optimal solution.The optimized results are validated by experiments.By means of panel riveting area division,a riveting path planning model based on GA-ACA is put forward,which set the shortest path,minimum maximum deformation and overall deformation uniformity as the goal.Through process optimization,the rank of the main factors and its effect on the local deformation are determined.The riveting path and global deformation are optimized,and the riveting deformation of panel could effectively been restrained.A lot of riveting deformation experiments,including single riveted structure,multi-riveted structure and MA700 panel,have been carried out to verify the riveting force calculation model,single rivet FE model,theoretical model for predicting riveting deformation of long strip plate and “local-global” mapping model for predicting panel riveting deformation,respectively.The results show that above proposed models have its effectiveness and accuracy.