| The hub is the core component of the helicopter transmission system,if the crack is not discovered in time,the crack will expand under the action of continuous external force,which brings great hidden danger to the flight safety of the helicopter.Therefore,it is of greate pactical significance to study how to detect the initiation and expansion of the hub crack in time to ensure the safety and reliability of the helicopter.In this paper,the finite element simulation software COMSOL is used as the research tool,and the helicopter hub is taken as the research object,acoustic emission characteristics of cracks in helicopter hub are simulated to meet the needs of acoustic emission detection system for cracks in helicopter hub.The main work content and research results are as follows:In this paper,a reasonable finite element simulation model of the titanium alloy two-dimensional flat plate is established by analyzing common representation method of crack acoustic emission source and calculating the time and spatial resolution of finite element simulation,which is simulated in COMSOL software.The lead-discharge acoustic emission experiment is designed to collect the lead-breaking signal on the titanium alloy plate.The rationality of the finite element method for acoustic emission modeling and simulation is verified by comparing the wavelet time-frequency diagram of the simulated signal,the plate theory group velocity curve and the wavelet time-frequency diagram of the experimental signal.In order to locate the position of the acoustic emission source reasonably in the simulation of the acoustic emission signal characteristics of the three-dimensional crack of the hub,firstly,this paper compiles the corresponding load spectrum according to the force of the hub in actual operation,and the weak area of the hub under the force is simulated in the COMSOL software.Then,the simulation 3D model is established in COMSOL software,the crack acoustic emission source is set in the weak area obtained by the load distribution simulation,and a series of gridded simulation measurement points are established in the area where the hub can actually place the sensor,and the crack acoustic emission simulation is performed.The simulation results show the propagation process of the elastic wave in the hub.In addition,the signal characteristic parameters received by the simulation measurement point are calculated and the spectrum is drawn.It is verified that the signal spectrum of the simulated measurement point is related to the force source function of the sound source.Finally,by changing the position of the sound source in the weak area,the measured point signal peak value combined with the signal characteristic parameter is used to filter and sort the measurement points.The simulation and sorting results provide the basis for the location selection of the helicopter hub acoustic emission detection sensor.In this paper,the tensile test of the hub material is designed.The acoustic emission signal of the specimen from the initial state to the fracture during the whole stretching process is collected.Combined with the load-time curve recorded by the test,the amplitude,energy,ringing count,arrival time,and spectrum change of the acoustic emission signal is analyzed during the fracture process.The analysis results show that the characteristic parameters of acoustic emission signals are related to the internal structural changes of materials.The acoustic emission signal spectrum of the titanium alloy is mainly concentrated at 130kHz-180 kHz,but the spectrum is different in distrinct mechanical stages. |
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