Numerical simulation of ultrasonic propagation and defect testing in laser cladding remanufacturing parts

Abstract

The laser cladding remanufacturing parts show typical anisotropic behaviors, which is difficult for acoustic detection. Therefore, the propagation behaviors of ultrasonic beam in the laser cladding remanufactured parts should be investigated in-depth, which will provides an important theoretical basis for ultrasonic nondestructive evaluation of this kind of parts. An ultrasonic measurement model for the laser cladding remanufacturing parts was developed. The influence of anisotropic laser cladding coating on the propagation behaviors of ultrasonic beam was analyzed. The propagation behaviors of ultrasonic beam in the laser cladding Fe314 alloy coating were investigated with the help of Rayleigh integral combined with Pencil method. The simulation results show that the influence of anisotropic material on the incident field due to the value of slowness, the direction of beam steering is determined by the normal vector of slowness surface, the beam focusing and defocusing behavior is determined by the curvature of slowness surface. The radiated ultrasonic field maintains a uniform distribution relative to the axis of the incident beam, when the direction of incident beam is consistent with or perpendicular to the grain orientation of laser cladding coating, which the directivity of beam is preferably. The reason lies in the incident direction of ultrasonic wave is perpendicular to the isotropic plane of crystal. In the radiated field of transverse wave angle probe, the transverse wave splits and the beam steers, separates with the change of grain orientation. The fundamental reason that transverse wave splitting due to the anisotropy of the laser cladding coating. The reason that beam steering lies in that the direction of group velocity (the direction of normal vector of slowness surface) is inconsistent with that of phase velocity (the direction of transverse wave vector). The slowness surface of anisotropic laser cladding coating is irregular in shape, the beam will appear in other angles in addition to the main beam, when transverse wave refraction. An ultrasonic measurement model for the laser cladding remanufacturing parts was developed by combining the beam model with the scattering model based on Kirchhoff approximation and Born approximation theory. This model can be used to predict the testing signals from the flaws in laser cladding remanufacturing parts. The accuracy of the provided model was verified by comparisons of the simulation results with the experimental results, both the signal amplitude and phase were in good agreement. Numerical simulation results provide an important theoretical basis for rational design of the process scheme of ultrasonic testing for laser cladding remanufacturing parts.