Simplified Modeling of Backscattered Noise and Attenuation Phenomena for Quantitative Performance Demonstration of UT Methods

Abstract

Sensitivity of UT methods in materials such as coarse-grained steels depends on attenuation and noise, due to scattering by microstructural heterogeneities. Here, existing UT simulation tools developed at CEA are modified to account for experimental observations of noise and attenuation. A model-based inversion tool is developed to estimate from experiments the parameters to input into the forward models. Example of application is given, showing the quantitative importance of these phenomena in terms of performance demonstration.

Application of time-frequency analysis in the case of ultrasonic imaging in a background of structural noise

“…During the analysis, the stochastic zone of scattering has been selected ( λ ≈ D, where D is an average grain size, λ is a wavelength). In such zone of scattering, the wavelength of the ultrasonic wave is close to the average size of a granule and scattering function is frequency (f) dependent and given by C D f c 1 ⋅ ⋅ ( / ) 2 (14)(15) , where C 1 is the material constant and c is the ultrasound velocity in the steel object. The results of the NDT simulation (Figure 1(b) and (c)), taking into account the influence of the structural noise, correspond to the results obtained by S Chatillon et al (14) .…”

“…For anisotropic material (composed of columnar grains), the variation in velocity may be significant (1)(2)(3)(4) . The essential feature of the granular structure numerical model is that it should be based on physical considerations, such as simulation of random granular structure of the material and simulation of propagation of ultrasonic waves in such medium (10)(11)(12)(13)(14) . For simulation of the granular structure there are two approaches.…”

“…It was assumed that reflections from boundaries of granules are dominating in generation of a structural noise (13) . In order to avoid large computational resources, another approach based on the set of the randomly distributed point type reflectors in order to mimic grain boundaries has been selected ( Figure 1(b)) (11)(12)(13)(14) . Frequency of the transducer has been selected according to the balance of the relation between the expected resolution and signal losses due to the scattering.…”

“…After propagation along a distance d, the wave amplitude is attenuated by e -α(λ,D)d , where α(λ,D) is the attenuation coefficient (caused by scattering) (14) . During the analysis, the stochastic zone of scattering has been selected ( λ ≈ D, where D is an average grain size, λ is a wavelength).…”

Modeling ultrasonic noise and attenuation in elongated duplex polycrystalline materials

“…Among the possible approaches proposed in the literature, we can mention the computation of structural noise signals by [1] and the modeling of statistical properties of signals by [2]. A method similar to the one of [1] was developed at CEA LIST [3]. In subsequent works, it was modified [4] so that the statistical properties of the generated signals match the outputs of a scattering model.…”