Nonlinear ultrasonic damage evaluation system research and development and its application on S355J2W steel for high speed train

The nonlinear ultrasonic (NLU) technique has been proposed to monitor structure health. It is well known that damage of materials is generally accompanied by increase of the materials’ nonlinearity. However, after processing such as welding, the microstructure of the material will change, which might affect the behavior of materials’ nonlinearity after degradation, further, inducing inaccuracy in evaluation of the structure life. An NLU system is developed to characterize the damage due to plastic deformation in S355J2W weathering resistant steel specimens which underwent different heat treatment processes. The experimental results show that the NLU system is effective and accurate for the measurement of higher harmonic components, and acoustic nonlinear parameters (ANP) increase with the increase of tensile stress. The results also show that ANP response relates to the grain size.