Electromagnetic Ultrasonic Surface Wave Acoustic Response Characteristics Of Metallic Plastic Damage

The plastic damage of metal components is an external representation of the accumulation of dislocation in the material under external loads.Long term tensile and cyclic loading of metal components will cause early degradation of mechanical properties.If adorable defects can be detected in time for early damage,the potential safety hazard will be eliminated and accidents prevented.Failure of metal components to detect defects during early damage stage will result in continuous accumulation of damage and eventually lead to fracture failure.How to detect and predict the failure of engineering structures efficiently and accurately will play an important role in the field of NDT.Electromagnetic ultrasonic testing technology is widely used in non-destructive testing of components such as metal plates and pipes.It has the advantages of no coupling agent,low requirement for material surface,easy to excite,and good repeatability.Based on the surface wave equation and nonlinear theory,the acoustic response characteristics of metal ultrasonic plastic surface damage are studied.The main work is as follows:(1)The electromagnetic ultrasonic testing method for plastic damage of metals are studied.The generation and detection methods of surface waves,the theory of nonlinear ultrasonic and the energy transfer mechanism of electromagnetic ultrasound transducer(EMAT)are described.The material model used to characterize plastic damage is analyzed.The feasibility of using the elastic-plastic damage theory model for non-linear ultrasound detection is studied,and the relative non-linear coefficient is used to characterize the degree of plastic damage inside metal materials.(2)The simulation and experiment of uniaxial tensile plastic damage of aluminum alloy are compared.A 2-D simulation model of tensile plastic damage based on elastoplastic model is established.By changing the plastic strain inside the material,different degrees of plastic damage are simulated to study the relationship between stress and plastic damage degree.Meanwhile,a quasi-static tensile experimental platform is built to load the aluminum alloy GB specimen.The plastic damage and deformation of the specimen under different tensile stress were studied.The results of the tensile simulation experiment are verified.(3)Simulation and experimental analysis of the acoustic response characteristics of electromagnetic ultrasonic surface waves on plastic damage of metals are carried out.Based on the elastic-plastic tensile model,the nonlinear electromagnetic ultrasonic surface wave elastic-plastic model is established to study the relationship among stress-strain,plastic damage and ultrasonic nonlinear coefficient under different plastic damage degree.The plastic damage specimen with tensile deformation is simulated and analyzed by the nonlinear electromagnetic ultrasonic experiment method.A non-linear electromagnetic ultrasonic surface wave detection system is built to detect the relative non-linear coefficient of the specimens with different plastic deformation,analyze the change rule of stress-strain and relative non-linear coefficient in different deformation stages of aluminum alloy materials,and then effectively monitor the change of plastic damage,and further evaluate the mechanical life of the materials.