Nonlinear Ultrasonic Guided Wave Mix Method For Characterizing High Temperature Creep Damage Of Alloy Steel

Alloy steel is widely used in key equipment such as pressure pipelines and chemical containers.Equipment under long-term service and severe conditions is facing potential performance degradation risks such as creep and fatigue.The nonlinear ultrasonic Lamb wave mixing detection method has the advantages of being sensitive to micro damage and high detection efficiency,so it is expected to be applied to the rapid detection and location of large-caliber pipeline damage.However,the multi-mode and dispersion characteristics of Lamb waves make it difficult to effectively excite and receive,which makes the research on the experimental and application basis of this method lacking.Therefore,research the mode selection and excitation effects of nonlinear ultrasonic Lamb waves will help promote the application of nonlinear ultrasonic Lamb wave mixing method in industrial inspection.For the problem of high temperature creep damage of alloy steel,this paper proposes to apply nonlinear ultrasonic Lamb wave mixing method to measure the damage.According to the theoretical conditions,the fundamental Lamb wave modes that can excite the mix wave are selected,verify the correctness of these modes through simulation.Experimental study on Lamb wave mixing measurement of high temperature creep damage was carried out.This method is used to characterize the high temperature creep damage of P92 and 316L steels,and the trend of nonlinear parameters is analyzed from the perspective of material microstructure evolution.This method provides the basis for characterizing high temperature creep damage of alloy steels by using the nonlinear ultrasonic Lamb wave mixing method.This article mainly researched from three aspects:(1)Aiming at the problem that the calculation time of filtering primary modes are relatively long,a calculation method for separating the symmetric mode and the antisymmetric mode is proposed,and a filter program of Matlab is written.At the same time,calculation of some necessary parameters is added,which reduces the time of filtering mix modes.The results of simulation calculation and experimental research show that the mode selected by the new program can effectively excite the mix wave signal.(2)In order to effectively excite strong mix signals,experimental researches on the influence of experimental parameters versus the generation efficiency of nonlinear mixing wave were carried out,the relationship curves of nonlinear parameters with experimental parameters such as frequency offset and period change were obtained.The results show that the amplitude of the mixed signal increases monotonically within a certain range with the increase of the excitation voltage of the transducer;the resonance conditions are destroyed when the excitation frequency is shifted from the center frequency of more than 0.08MHz,which lead to a sharp decrease of nonlinear parameters;the increase of the number of fundamental signal cycles can improve the signal-to-noise ratio of the mixed signal under certain conditions.Therefore,increasing the excitation voltage within a certain range can generate a stronger mixed signal,and increasing the number of signal periods can improve the signal-to-noise ratio of the mixed signal in the frequency domain.(3)Two types of alloy steels(P92 and 316L)with high temperature creep damage were measured by nonlinear ultrasonic Lamb wave mixing method,the relationship curve between the nonlinear parameters of mixing wave and high temperature creep time was obtained.The curve shows a rising-steady-rising trend.The microstructure evolution of 3 16L specimens with different creep time was studied,and the relationship between the tissue evolution and the change of nonlinear parameters was analyzed.The results show that the initial upward trend is due to the continuous increase in dislocation density,and the relatively stable trend in the second stage is due to the precipitation of solute atoms in the alloy material as the strengthening phase to form a precipitated phase that hinders grain boundary slippage and dislocations.The sharp rise of the nonlinear parameters in the final stage is related to the precipitation nucleation.Therefore,the nonlinear ultrasonic Lamb wave mixing method can characterize the change of the microstructure of the material to a certain extent.