| Pneumatic hammer rivet is a common connection method in riveting,because of its unique advantages,it is widely used in aircraft assembly,especially in areas with limited space and complicated curved surfaces.The quality of riveting determines the assembly quality,service performance and fatigue life of aircraft.It is of great significance to study the principle of pneumatic hammer riveting for riveting quality.At present,the research on riveting mostly uses finite element method and experimental method,the research object of finite element method mostly focuses on riveting,the research object of the experimental method is the damage of the vibration in the pneumatic hammer riveting,research on the field of pneumatic hammer riveting has not been involved and requires in-depth research.In this paper,the pneumatic hammer riveting is taken as the research object.The dynamic deformation mechanism of the rivet in the hammer riveting process is studied by introducing the theory of impact dynamics.The finite element simulation model of pneumatic hammer riveting is established based on the theory of impact dynamics in pneumatic hammer riveting.The model was verified by the existing experimental platform.The main research contents of this paper include:(1)Based on the research and analysis of the mechanism of pneumatic hammer riveting process,abstracting the "piston-rivet-rivet" in the riveting system as the high-speed impact of three rod-shaped parts,and introducing the impact dynamics to analyze the transmission of stress waves in the collision between the piston and the hammer,the hammer and the rivet,the internal stress propagation law and deformation mechanism during the riveting process provide the basis for the matching of rivet and hammer,at the same time,the influence of the top tightening force on the rivet forming is discussed,and the characteristics of the material during the impact process are studied.(2)Based on the analysis of impact dynamics,the finite element simulation model of pneumatic hammer riveting is established,the stress-strain relationship of rivet under high-speed impact is used in the modeling process.To the propagation of stress waves,the data transmission method is used in the modeling to realize the output and input of the front and rear impact data,and accurately simulate the multiple impact process.The finite element model can not only accurately reflect the riveting process of pneumatic hammer,but also verify the influence of top force on riveting process of pneumatic hammer.(3)Based on the analysis of pneumatic hammer staking forming mechanism and finite element simulation modeling,the experimental verification was carried out on the existing riveting test bench.The experiment included standard hoe height test,3.5mm hoe height test and 4.5mm hoe height test.The correctness of the modeling method was verified by the standard height test of the Shantou.At the same time,the influence of the top tightening force on the forming was verified.The height of the tamping test proved the correctness of the finite element modeling method from different stages of rivet forming.The model can reflect the characteristics of each stage of the pneumatic hammer riveting,and the distribution of the interference amount of the rivet under different hammer heights is obtained. |
