Research On Interference Control Of Composite Structure In Electromagnetic Riveting

Composite material has been used widely in aerospace and other fields because it has a series of characteristics such as high strength,light weight and so on.At present,the delamination and cracking in the joining of composite material structure are the key problems to be solved in production.Electromagnetic riveting(EMR)is a new kind of riveting process.EMR has the advantages of stable riveting quality and the uniform deformation of rivet shaft.It thus provides an effective way to realize the joining of composite material structure.The EMR process of composite material structure is affected by many process parameters.And the relationship between the process parameters and interference is to be determined.In this thesis,the relationship between process parameters and interference was investigated and the method of interference control was explored from macro and micro aspects by numerical simulation and experiments combination methods.The EMR process of composite material structure was analyzed by finite element method based on the ANSYS software.The simulation results showed that the cycle of EMR process was about 8ms and the discharge current by simulation was agreed with the current measured.The distribution of magnetic force in the drive plate was uneven and there was an obvious skin effect.The deformation of rivet headand the distribution of interference were analyzed at different process parameters.The relationship between process parameters and interference was explored and the control of interference was realized.The results showed that the distribution of interference was uniform along the rivet shaft direction in the EMR process.And the relative interference was controlled from 0.50%to 0.95%.The effects of different process parameters on the size of rivet head and interference were studied by the process experiment.The results showed that the interference was more even in the EMR process.The interference increased with the increase of discharge voltage,the decrease of the rivet overhang and the increase of the riveting die angle.The relative interference was large by the riveting die with angle and it was easy to damage the composite material.In the low voltage EMR process,the best discharge voltage was 135V and the rivet overhang was 0.9d to 1.0d.The washer size was 9mm×4.10mm×1mm and drive plate thickness was 8mm.And the diameter between rivet and hole was 4.20mm.They were agreed with the simulation results.The samples were analyzed from macro and micro aspects at different loading conditions including pneumatic riveting,pressure riveting and high and low voltage electromagnetic riveting.The result showed that the rivet head formed was a drum and the expansion of rivet shaft was uniform in the low voltage electromagnetic riveting process.And the riveting quality was good.The brush structure was formed around the hole wall and it was helpful to improve the structure strength and fatigue life.Static strength test showed that the shear strength of the riveting structure improved with the increase of interference.The interference increased about 1%and the shear strength increased 7.6%to 10.7%by using riveting die with 50 angle.Pulled off strength depended on the uniformity of the interference distribution.Pulled off strength in the electromagnetic riveting was 24%to 58%higher than that of pneumatic riveting and pressure riveting.