FEM simulation and experimental validation of a non destructive technique applied to rolling bodies.

FEM simulation and experimental validation of a non destructive technique applied to rolling bodies. In this thesis nondestructive methods for the characterization of surface cracks in rolling components using ultrasonic Rayleigh waves are discussed. Rayleigh waves propagate near the free boundary of a solid. As the energy associated with the Surface Acoustic Waves is concentrated in a small layer in the vicinity of the surface they are particularly sensitive to surface discontinuities. Furthermore, Rayleigh waves follow complex curvatures and consequently, often provide insight into defect areas that are inaccessible to other wave forms. Nondestructive testing using Rayleigh waves is therefore a promising technique for the inspection of components such as ball bearings and other rolling bodies, where cracks are expected to form on the surface of the component. The existing Non Destructive Testing methods includes optical method, eddy current method and by measuring vibration of ball bearings. But all these methods are only sensitive to surface defects. Since we know that under working condition failure starts at a point below the surface. So it is of major interest to evaluate the subsurface defects if present. The near-field scattering of a Rayleigh wave at a crack on a spherical surface is studied theoretically and experimentally. FEM Package Abaqus 6.14 is used for the modeling of ultrasonic wave propagation while material used in simulations is 100Cr6 which is widely used for the production of ball bearings. The transient analytical solution of the scattering problem is obtained by the extension of an existing time-harmonic solution and scattering process is visualized numerically by implementing a finite difference scheme. The near-field analysis is based on a procedure that allows the Rayleigh waves to be distinguished from the other wave modes scattered at the defect. Comparison of the simulation results at different frequencies allows for the evaluation of specific crack modeling approaches. Different methods are investigated for the solution of the scattering problem, i.e. determination of the crack size on the basis of measurements in the scattered near field. The time-of-flight (TOF) method is validated for crack depths larger than the wavelength of the incident wave. On the basis of analytical results the time delay of the transmitted wave is correlated with the depth of the crack. On the other hand defects smaller than the wavelength can be evaluated by measuring and comparing displacement history of defected component with the non-defected. The characterization method introduced here to investigate the presence of defect is the attenuation in the displacement signal also we can uses time reversal numerical simulations (TRNS) for the determination of the crack position and crack length in which resulting waves propagate back through the medium and interfere at the position of the original source. The transversal displacements are measured at the specific nodes of interest and the displacement histories are measured and compared at the surface of the specimen, reversed in time and used as excitation in a numerical simulation. Plots generated shows the comparison of wave signal monitored at sensor node. The defected signal shows the significant attenuation in magnitude and slow arrival time due to scattering around the defect.