Simulation And Experiment Study Of Nonlinear Ultrasonic Detection Of Stress Corrosion Micro-crack Damage In Stainless Steel

Austenitic stainless steel has excellent performance and has been widely used.However,the stress corrosion damage is very harmful as one of the main damage forms of stainless steel components.Once the stress corrosion micro-crack develops,brittle fracture of the component will occur quickly and even lead to catastrophic accidents.The linear ultrasonic characteristics of micro-crack are not obvious,however,the nonlinear ultrasonic detection technology can effectively detect the micro-crack.Based on the above,in this paper,the nonlinear ultrasonic detection of stress corrosion micro-crack damage is studied and discussed mainly by numerical simulation method and auxiliary test method.The main work contents are as follows:1.The basic theory of nonlinear ultrasonic detection is summarized,which provides theoretical support for the nonlinear ultrasonic detection technology selected in this paper.In addition,the mechanism of stress corrosion damage and the basic theory of finite element simulation are introduced,and it is clear that the research is studied on the theoretical basis by means of finite element numerical simulation and experiment.2.ANSYS and ABAQUS software are introduced in detail.In addition,the modeling idea of simulation in this paper is expounded: the reconstruction method is used to realize the coupling between stress field and ultrasonic field based on the elastic-plastic deformation constitutive relation by means of ANSYS and ABAQUS software.The optimal combination of parameters in the numerical model is determined and the correctness and effectiveness of the model are verified.3.The influence of micro-crack width and depth,stress direction(tension/ compressive)and magnitude on the propagation characteristics of nonlinear ultrasonic surface wave under constant stress are discussed.According to the research findings:(1)Under constant load,the nonlinear coefficient decreases monotonically with the increase of the width of the micro-crack,and increases monotonically withe the increase of the depth of the micro-crack.Compared with the free state,the response of the constant stress to the nonlinear effect becomes more and more significant with the increase of the micro-crack depth.(2)The compressive stress makes the slapping and sliding effects stronger,thus leading to the enhancement of the nonlinear effect,while the tensile stress makes the nonlinear effect weaker.(3)The nonlinear parameters and the normalized Fourier transmission coefficients decrease with the increase of tensile stress and monotonically increase with the increase of compressive stress.(4)The limit width of micro-crack is related to the stress state.The larger the tensile stress,the smaller the limit width.The effect of compressive stress is the opposite.(5)The excitation mode of excitation sound wave directly affects the ability to detect defects.The energy of the acoustic wave excited by the line source is obviously higher than that of the acoustic wave excited by the point source,so the limit width of the micro-crack can be detected by the line source is also larger than that of the point source.4.A stress corrosion test platform was built,and then the nonlinear surface wave ultrasonic detection was carried out for 304 stainless steel stress corrosion damage under different corrosion time,and the nonlinear parameters characterizing the damage were extracted.After that,the dimension of damage was measured and brought into the finite element model.The nonlinear parameters obtained are in good agreement with the experimental results,and the validity of the finite element model is verified.