Modeling of ultrasonic propagation in a diffusing metallurgical structure, application to NDC

Scattering phenomena can interfere with the ultrasonic non destructive testing of certain materials. It occurs for example in the testing of certain types of steels used in nuclear power plants, or of titanium alloys used in aeronautics. The scattering of ultrasonic waves by the microstructure of those materials induces structural noise and attenuation, which can have a significant impact on detection performances. This thesis deals with the modeling and computing of those phenomena. A model is used to determine the scattering properties of a metal, based on its microstructure. This model was adapted to different categories of metals. A method to compute structural noise based on this model was developed. It relies on the pencil method to perform semi-analytical computations of tridimensional ultrasonic fields. An original approach is used to limit the time necessary to compute noise signal. The computation is based on outputs of the model. This approach is based on the single scattering approximation. Noise signals computed using this method were compared to experimental results. Those comparisons confirm the relevance of the method. They also illustrate the importance of interference phenomena in structural noise. A second computation method that takes into account multiple scattering has been studied. It is based on a Monte-Carlo method applied to the radiative transfer theory. (author)