Modeling ultrasonic pulse-echo signals from ellipsoid inclusions in immersion testing

Abstract

In order to statistically estimate the characteristics of flaws in components based on ultrasound measurement results, a model for ultrasound measurement simulation is needed. One such model is the Thompson-Gray ultrasound measurement model, which capabilities in modeling the ultrasound measurement result for different flaw cases and applicability to future research is evaluated in this master’s thesis.

The Thompson-Gray model considers the wave propagation in a component as well as the wave scattering from a defect in the component. Wave propagation terms in the Thompson-Gray model are calculated using the multi-Gaussian Beam model and the scattering amplitude of defects is calculated using the modified Born and Kirchhoff approximations. The influence of the electrical components in the measurement system is also considered in the model with a system function, that is determined from reference measurements.

Ultrasound measurement results are calculated for five different flaw cases. In all cases, a single-element transducer is used in pulse-echo mode in immersion. The flaw cases include a spherical pore in fused quartz and spherical and ellipsoid aluminium oxide and manganese sulfide inclusions in quenched and tempered steel.

Model verification is done by comparing the results calculated with the Thompson-Gray model to those obtained by finite element simulation. Finite element models are built using COMSOL Multiphysics. Results for the first flaw case are also compared to actual measurement data.

In all flaw cases, the results calculated with the Thompson-Gray measurement model and finite element simulation agree on both the timing and the amplitude of the early time response of the flaws. In later arriving responses, the Thompson-Gray model underestimates the amplitude of the response. Timing of the later arriving responses also differs between the Thompson-Gray and finite element results.

As the Thompson-Gray measurement model predicts the early time response of different flaws reliably, the model can be used in future research as the foundation of a statistical model. To get more information about the way the Thompson-Gray model results differ from real measurement results, the finite element models should be revisited.