Fatigue Damage Detection Based On Dynamic Measurement

Fatigue is one of the main failure modes of mechanical part.The detection of fatigue damage has always been a research hotspot in the material and mechanical fields.For the urgent need of online detection and nondestructive testing,this thesis is aimed to develop fatigue damage detection methods using dynamic measurement,which provides new means for investigating fatigue evolution of fatigue specimen.When the fatigue specimen is subjected to cyclic loading,complex dynamics characteristics such as impact and friction are generated due to the presence of internal damage.These dynamic behaviors are coupled with the applied cyclic loading signal,resulting in that the vibration response of the fatigue specimen exhibits typical cyclostationary characteristic.The conducted work is listed as follows:1)An algorithm for processing the cyclostationary signal is programmed and applied to fatigue specimen testing.The damage characteristic parameters(such as cyclic frequency spectrum area)are defined based on the second-order cyclic statistics of vibration signals,and the fatigue damage(online)detection method under cyclic loading is established.2)Using the Simulink simulation platform,the uniaxial fatigue dynamics system simulation model is constructed.The proposed method is illustrated on numerical fatigue model,whose effectiveness is validated.3)Cyclic loading fatigue tests are Carry carried out,a vibration signal acquisition system is built.The proposed damage characteristic variable(e.g.,cyclic frequency spectrum area)is found to be sensitive to the fatigue damage.Cyclostationarity based damage detection is susceptible to the working conditions of the testing machine.The transmissibility function defines the transfer model between responses of the fatigue specimen at different places,which can in principal eliminate the influence of the input load of the testing machine.Therefore,this thesis also develops the damage detection method by using the transmissibility function.The main ingredients are as follows:1)The broadband signal is used as the input load of the testing machine,and the vibration signal acquisition platform for the sample is built.The spectral estimation algorithm is applied to establish a high-accuracy estimation method for the transmissibility function.2)Base on the Simulink simulation platform,the uniaxial fatigue transmissibility model is established.A filtered Gaussian noise is used as excitation signal.The estimated force transmissibility function is used to study the damage evolution process.3)A sweeping signal is considered as input load of the testing machine,the transmissibility function between the acceleration responses at different positions of the fatigue specimen is estimated,and the damage characteristic variable is constructed to study the evolution of fatigue damage.Simulation analysis and fatigue testing results both verify the feasibility of the above two methods of fatigue damage detection based on dynamic measurement,which lays the foundation for the investigation of fatigue damage evolution and anti-fatigue manufacturing process.