Crack Monitoring Method For Aerospace Aluminium Alloy Riveted Structures Based On Eddy Current Effect

Aircraft aluminum alloy sheets have advantages such as high strength and light weight,and are widely used in aircraft body structures.In the aircraft manufacturing process,riveting technology is widely used for connecting and fixing aircraft structures due to its advantages of strong structure,easy disassembly and maintenance.During flight,the aircraft body will experience strong turbulence and vibration when encountering air currents,and factors such as extreme high and low temperatures,icing,lightning,and high-strength radiation fields can cause corrosion,pitting,and fatigue cracks at the edges of rivet holes in the aircraft aluminum alloy,leading to failure of the strength properties of the riveted structure and damage to the structural integrity of the aircraft.If these defects cannot be discovered in time,it may ultimately cause a serious accident resulting in loss of life.In response to the problem of cracks generated around rivet holes,this article proposes a crack monitoring method based on eddy current effects to achieve crack monitoring of the edges of rivet holes in aircraft aluminum alloy sheets.In order to verify the feasibility of using eddy current to monitor cracks around aluminum alloy rivet holes,a finite element simulation software was first used to establish a single excitation single receiver detection model and a single excitation dual receiver eddy current monitoring model,and analyze the effect of cracks in aircraft aluminum alloy sheets on the distribution of eddy current density in the sheet.The distribution of eddy current with and without cracks was compared to prove the feasibility of using eddy current for crack monitoring around rivet holes.Then,by changing the excitation frequency and coil structure parameters in simulation experiments,the distribution law of eddy current density under different parameters was obtained,providing a basis for the design of eddy current monitoring coils.The simulation results show that the single excitation single receiver detection model can only detect whether there is a crack in the aluminum alloy sheet,while the single excitation dual receiver model can not only detect whether there is a crack in the aluminum alloy sheet,but also determine the location of the crack when it appears.Compared with the single excitation single receiver detection mode,the single excitation dual receiver mode has better detection performance.To achieve online monitoring of cracks at the edges of aircraft aluminum alloy rivet holes,a flexible eddy current sensor for monitoring cracks at the edges of aluminum alloy rivet holes was designed,and an eddy current monitoring system was built.Static tests and dynamic loading tests were performed on specimens with pre-made X-directional cracks,Ydirectional cracks,and rivet joints without cracks,and experimental data under different conditions were obtained.The experimental results show that when cracks occur in the aluminum alloy sheet,the induced voltage in the receiving coil on the side with the crack will increase,while the induced voltage in the receiving coil on the other side will remain basically unchanged.Therefore,the presence of cracks around the rivet hole and which part of the sheet has the crack can be determined based on the magnitude of the induced voltage in the receiving coil and the position of the receiving coil.This proves that the crack monitoring of the edges of aircraft aluminum alloy rivet holes using eddy current effects proposed in this article is feasible,providing a method and approach for crack monitoring at critical locations in aircraft structures.