Research On Metal Fatigue Damage Detection And Location Based On Nonlinear Ultrasonic Mixing

Metal materials suffer a lot from fatigue damage and cause accidents under long-term cyclic loading.Therefore,it is important to identify and locate early fatigue damage in metal structures in time.Nonlinear ultrasound effect is sensitive to this early damage and can effectively characterize damage structures.Based on the theory of nonlinear acoustics,this paper studies the fatigue damage detection and localization of metal materials.This paper carries out simulation work based on ABAQUS software: the Mechanism of contact acoustic nonlinearity is studied and it reveals the action process of sound waves and damage structures.For different health status metals,wave-mixing models from the same direction excitation are established,and it shows that wave-mixing method can realize the damage detection of metals.The effects that in-plane and out-of-plane displacement,excitation signal length,stress loading strength have on mixing signal amplitude are analyzed,and the results provide reference for excitation parameter design to produce obvious mixing effects.Wave-mixing models from different direction excitation are established to study the influences of speed,distance,and collision on energy in Al6061-t6 material,and it provides reference for positioning algorithm based on different delay time,and the optimized parameters are proved effective for the location of damage structure.Time-Frequency analysis method is used to analysize of mixing signals under different cycle excitation,and a method for obtaining characteristic time values of target mixing signals is proposed by wavelet coefficient matrix looking-up table method,then a fatigue damage localization algorithm based on time-frequency analysis theory is proposed.This paper also studies error analysis of the proposed algorithm including the length of the excitation signal,the distance between the receiving point and the crack distance.The results show that the effectiveness of the localization algorithm in the error tolerance range,and it enriches the fatigue damage localization method.This paper also sets up wave-mixing experiment system from different direction excitation,and determines the mixing detection to optimize the excitation conditions.Studing delayed positioning algorithm for with and without cracks samples,and the experimental results show that the delayed positioning algorithm can effectively detect and locate the early fatigue damage of metal materials.