Model And Application Of Assembly Deviation For Large Stiffened Thin-walled Structure

Stiffened plate structure is widely used in aerospace field,as the main bearing skeleton of heavy launch vehicle.The assembly quality directly determines the reliability of aerospace products.The complex residual internal stress field of stiffened plate causes serious warping deformation after milling.Moreover,the rolling bending process is affected by the residual stress of milling and the anisotropic characteristics of the stiffened plate,so it is difficult to accurately control the bending radius of the plate.Due to the stiffness difference between the plate and stiffener,the deformation of stiffened plate presents geometric nonlinearity,which makes the calculation of the assembly deviation more difficult.It is important to establish a stiffened plate model that accurately describes the large rotation deformation problem,to explore the correlation between the manufacturing and assembly deviations of stiffened plate structures,so as to improve the assembly quality and efficiency of heavy launch vehicle.In this paper,a new plate/plate composite element model is proposed based on the absolute nodal coordinate formulation to describe and calculate the manufacturing and assembly deviations of stiffened plate structures.The manufacturing deviation caused by milling and rolling is investigated by using FEM.Based on the deformation compatibility condition,a quasi-static method is used to calculate the assembly deviation of stiffened plate structures.On this basis,the calculation model of assembly deviation for circular tube enclosed structure is established,and the evaluation criteria of assembly quality for enclosed structure is put forward.For the assembly process of circular tube of heavy launch vehicle,the FEM numerical analysis is used to verify the feasibility and accuracy of the new model.The main research contents of this paper include the following parts:(1)New plate/plate composite element model based on ANCFAccording to deformation compatibility condition,a new plate/plate composite element model is established to solve the separating or penetrating problem between plate and stiffener when using plate/beam element under large warping deformation.The stiffness and mass matrixes are derived based on the nonlinear continuum mechanics theory.The convergence and accuracy of the new model are proved by numerical simulation,and the influence of size and number of stiffeners on the performance of the new element model is analyzed.(2)Definition and calculation of manufacturing deviationThe deformation state and deviation distribution of stiffened plate structures after milling and roll forming are analyzed by using FEM.Based on the stress state of stiffened plate after milling and rolling,the occurrence mechanism of warping and bending deformations is analyzed.According to the typical deformation of the stiffened plate,the initial manufacturing deviation is defined.By using the coordinates of characteristic points to fit the response surface equation of the structure,the initial manufacturing deviations are obtained.It provides possibility for quantitative analysis of assembly deviation of stiffened plate.(3)Calculation of assembly deviation for stiffened platesBased on the new plate/plate composite element model,the stiffened plate structure is discretized,and the generalized external force and stiffness matrixes are derived.Using the quasi-static hypothesis,the assembly process of stiffened plate structures is simplified into two basic steps of sizing and spring-back.According to deformation compatibility condition,the spring-back deformation after sizing is calculated,and then the deviation calculation model of the assembly process of stiffened plate structures is established.The changing regularity of assembly deviation under different initial manufacturing deviations is quantitatively analyzed.(4)Calculation of assembly deviation for circular tube structureBased on the assembly deviation model of stiffened plate structures,a model for calculating assembly deviation of circular tube enclosed structure is developed.The evaluation criteria of assembly quality for enclosed structure is put forward according to the geometric characteristics of circular tube structure.The influence of initial manufacturing deviation form and value,the assembly sequence and the size of stiffened plates on the assembly quality of circular tube of heavy launch vehicle is studied.The accuracy of the assembly deviation model is investigated by comparing the results of calculation and numerical analysis.In this paper,a method for assembly deviation calculating is proposed to describe the relationship between manufacturing deviation of stiffened plate structures and assembly deviation of circular tube enclosed structure,which provides a theoretical basis and a guidance for the prediction and control of assembly deviation of heavy launch vehicle in the future.