Nonlinear Rayleigh Wave Detection Of Early Fatigue Damage On Gas Turbine Blade Surface

As an important energy conversion component of gas turbine in power plants,gas turbine blades have a harsh working environment,so that they are prone to damage and even break suddenly.In order to avoid accidents of gas turbine,it is necessary to detect early damage of the blade.Nonlinear ultrasonic is very sensitive to micro-defects inside the material and can detect early fatigue damage of the blade.However,the damage is mainly generated on the blade surface.In addition,the blade has the structural characteristics of large area,variable curvature and variable thickness,which brings difficulties for the detection of the blade.In this paper,the 0Cr17Ni4Cu4 Nb martensitic stainless steel of gas turbine blade as the research object,a nonlinear Rayleigh wave detection method is proposed to study the non-linear characteristics of 0Cr17Ni4Cu4 Nb steel under different fatigue degrees.The propagation characteristics of Rayleigh wave on blade surface and the relationship between the ultrasonic nonlinearity coefficient of Rayleigh wave and the fatigue life of 0Cr17Ni4Cu4 Nb steel were studied by finite element simulation and experiment.At the same time,a rapid detection method for early damage of the blade surface is proposed.The main research contents are as follows:(1)A high-precision nonlinear Rayleigh wave detection hardware system was built.The ultrasonic signal acquisition and processing system was programmed by LABVIEW platform,and the corresponding fixture was made according to the measured object.(2)Aiming at the structural characteristics of variable curvature and thickness of gas turbine blades,the corresponding finite element models are established.The infinite element is introduced into the boundary of the models,which effectively prevents the reflection of the boundary from waves.The influence of different curvature and thickness on Rayleigh wave propagation characteristics is obtained by simulation,and the Rayleigh wave detection depth of 0Cr17Ni4Cu4 Nb stainless steel surface defect is numerically simulated.(3)The three-point bending fatigue damage nonlinear Rayleigh wave detection was carried out on the surface of two different sizes of 0Cr17Ni4Cu4 Nb stainless steel samples by using the built-in detection system,which obtained the relationship between Rayleigh wave ultrasonic coefficient and material fatigue life.Furthermore,the finite element model of nonlinear Rayleigh wave detection for surface fatigue damage of samples was established.The relationship between the nonlinear coefficient of ultrasonic and the length and number of surface micro-defects was obtained,which verified the experimental results.(4)In order to satisfy the need of large-area rapid detection of gas turbine blades,a method of inverse relative nonlinear Rayleigh wave detection is proposed,and simulation and experimental verification are carried out.This method effectively improves the ultrasonic nonlinear coefficient of Rayleigh wave and increases the detection efficiency.