Optimization Of Magnitude And Layout Of Pressing Force For Composite Aerostructure Assembly

Based on the excellent mechanical properties,composite material has been widely used in aircraft.The low precision of molding and the accumulation of assembly error result in assembly gap between components.Pressing force is often used to eliminate the assembly gap in engineering,however,inappropriate pressing force not only hardly eliminate the gap,but also may cause damage between the layers of the composite components.In this paper,the optimization model with magnitude and layout of pressing force was established to improve the effect of the gap-elimination as well to avoid the damage.Finally,the optimum solution was analyzed by finite element analysis and experiment.The research work of this paper mainly includes:(1)Based on studying the components of the composite assembly pressing force,analyzing the wing box structure,assembly process and assembly tooling,the research model of composite wing box assembly was established.After simplifying the research model,initial gap was set as 0.5mm,with laminates delamination as the constraint condition,elimination rate of assembly gap as the objective function,the optimization model with magnitude and layout of pressing force was established.According to the characteristics of the problem,the genetic algorithm was chosen to solve the problem.The programs were written in Python,the parameterized finite element model was calculated in ABAQUS,and the algorithm of interference checking and repairing was added to the genetic algorithm,which avoided invalid calculations,and improved the computational efficiency effectively.(2)Taking a model with initial gap of 0.5mm as an example,optimal solution was analyzed by the combination of experiment and finite element method.The pressing force was measured and controlled by pressure sensor which was on the top of the compression.The effect of gap-eliminating by the optimum solution was studied.The strain field distribution and the delamination damage were measured by 3D VIC.The results showed that the optimized pressing force could eliminate the gap much more effectively.The elimination rate reached 93.75%,which was 50.7% higher than that before optimization.The strain field distribution tended to be much more uniform,and there is no obvious concentrated area.Comparing FEA with experiment,it can be seen that the result of finite element analysis was consistent with the result of experiment,which proved that the finite element model had high accuracy.By setting cohesive element in the finite element model,it was known that the stress and strain distribution was uniform,and the optimized pressing force did not cause delamination damage to the composite.(3)The universal fitness of optimum solution was studied by setting different initial gaps.With initial gap of 0.2-0.8mm,by finite element analysis and experiment,the influence to strain field distribution and gap-eliminating before and after optimization were analyzed.The experimental results showed that when the initial gap is 0.2-0.8mm,the optimized solution improved the gap elimination rate to 85.42%-100%,which was 26.31%-115.82% higher than that before optimization.The research results showed that the optimum solution was universally suitable for different initial assembly gaps.