Simulation of structural noise and attenuation occurring in ultrasonic NDT of polycrystalline materials
In some polycrystalline materials, ultrasonic non destructive testing is affected by structural noise and attenuation. Those phenomena can cause significant loss in detection performances, thus their prediction is of great practical interest. During previous works at CEA-LIST, noise and attenuation models have been developed and implemented into the simulation software for non destructive testing CIVA. These two models are based on distinct methods and both require reference ultrasonic measurements to reproduce the behavior of a given material. The main purpose of this work is to improve these models by linking structural noise and attenuation to the microstructural parameters. This should suppress the need for reference measurements and allow for more accurate simulations. In this communication, a method using one scattering model to compute both structural noise and attenuation is presented. This method is based on the assumption that both phenomena can be considered to depend only on the average of the energy scattered by a unit volume of the material. A model based on the Born approximation is used to relate this averaged scattered energy to second order statistical properties of the microstructure and to the elastic properties of a single crystallite. This model is valid in a frequency domain larger than the Rayleigh domain. During the simulation of the testing of a polycrystalline material, a non-attenuated ultrasonic field is firstly computed. Attenuation is applied afterwards using a timedependant filtering. Noise is simulated by generating a random set of point-like scatterers in the medium. Mode conversions and phenomena related to anisotropic scattering are accounted for. Simulation results obtained with this approach are compared to experimental results.
KeywordsGrain Size Distribution Attenuation Coefficient Polycrystalline Material Born Approximation Noise Generator
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