Study On The Detection And Evaluation Method Of Second Harmonic Lamb Wave For Fatigue Damage Of Plate Structure

As a common form of structure,metal plate structure is widely used in all kinds of important infrastructure because of its good formability and weldability.Under the long-term action of alternating load,different degrees of fatigue damage will occur in these metal plate structures,resulting in the decrease of their bearing capacity.According to statistics,more than 80% of the failure of mechanical parts is caused by fatigue damage.Aiming at the detection demand of fatigue damage in plate structure,this paper studies the harmonic nonlinear ultrasonic detection and evaluation method of fatigue damage in plate structure.Specific research contents include:(1)Numerical simulation of second harmonic lamb wave detection for fatigue damage of plate structure.Based on the classical nonlinear ultrasonic theory,the mode pairs and corresponding frequencies of second harmonic lamb waves with cumulative growth effect are determined.The nonlinear lamb wave detection simulation model of plate structure was established,and second harmonic lamb wave detection numerical simulation was carried out to study the influence of detection parameters(mode type,excitation frequency)and loading mode on second harmonic generation effect.The results show that the two lamb wave modes have obvious regularity to the variation of the second harmonic nonlinear parameters with the material properties,and can be used to characterize the variation of the material properties of plate structure.(2)Second harmonic lamb wave test for fatigue damage of plate structure.An experimental study on nonlinear lamb wave detection of fatigue damage of metal plate structures was carried out.The detection results show that the polarity reversal treatment can effectively enhance the amplitude and signal-to-noise ratio of the second harmonic lamb wave component in the detection signal.The second harmonic nonlinear coefficient and stress wave factor of the two lamb wave modes show a monotonously increasing trend with the increase of fatigue damage,and the S2-S4 mode pairs are more sensitive to fatigue damage.(3)Study on ultrasonic evaluation method for fatigue damage of plate structure.Based on the typical probabilistic statistical distribution model,the ultrasonic evaluation method for fatigue damage of plate structure was studied.Based on the similarity analysis of lamb wave detection signals under different damage states,a new method to characterize the fatigue damage of plate structures was developed.Based on the extracted T statistics,second harmonic nonlinear coefficient and stress wave factor,the effects of four typical probabilistic statistical distribution models on the fatigue damage evaluation of plate structure were studied.The results show that all the three parameters can be used to evaluate the fatigue damage of plate structure,but the three parameters have different effects on the fatigue evaluation and are greatly influenced by the type of probabilistic statistical model.