The ultrasonic TOFD (Time of Flight Diffraction) Technique is commonly used to detect and characterize disoriented cracks using their edge diffraction echoes. An overview of the models integrated in the CIVA software platform and devoted to TOFD simulation is presented. CIVA allows to predict diffraction echoes from complex 3D flaws using a PTD (Physical Theory of Diffraction) based model. Other dedicated developments have been added to simulate lateral waves in 3D on planar entry surfaces and in 2D on irregular surfaces by a ray approach. Calibration echoes from Side Drilled Holes (SDHs), specimen echoes and shadowing effects from flaws can also been modelled. Some examples of theoretical validation of the models are presented. In addition, experimental validations have been performed both on planar blocks containing calibration holes and various notches and also on a specimen with an irregular entry surface and allow to draw conclusions on the validity of all the developed models.

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For several years, the World Federation of NDE Centers, WFNDEC, proposes benchmark studies in which simulated results (in either ultrasonic, X-rays or eddy current NDT configurations) obtained with various models are compared to experiments. This year the proposed UT benchmark concerns inspection configurations with multi-skips echoes. This technique is commonly used to inspect thin specimen and/or in case of limited access inspection. This technique relies on the use of T45° mode in order to avoid mode conversion and to facilitate the interpretation of the echoes. To evaluate the influence of the beam divergence on the detectability after several skips, inspections were done with two probes working at 5MHz, with two different apertures. To simplify coupling conditions and probe parameters adjustment, inspections were done using full immersion technique.

The ability to measure early-stage high-temperature hydrogen attack (HTHA) has been improved by the use of optimized ultrasonic array probes and techniques. First, ultrasonic modeling and simulations were performed to design a set of array probes. The data was then collected using phased array ultrasonic testing (PAUT) and full matrix capture (FMC) techniques. Damage visualization, characterization, and sizing was completed with PAUT, total focusing method (TFM), and adaptive total focusing method (ATFM) advanced algorithms. The detection and sizing capabilities were initially validated on steel calibration samples with micromachined defects and synthetic HTHA damage. Vessels with suspected HTHA damage were removed from service, inspected with multiple array techniques, and then destructively evaluated for a results comparison with metallographic images. This study concluded that the FMC/TFM/ATFM techniques and algorithms improve detectability, characterization, and sizing of early-stage HTHA damage as compared to PAUT.

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A model coupling viscoelastic and multiple-scattering losses is developed to predict ultrasonic attenuation in unidirectional fiber reinforced composite of high fiber volume fraction. Complex-valued stiffness constants accounting for viscoelasticity are inserted in classical multiplescattering theory. Waves of various polarities (SH, SV, L) relatively to the fiber direction are considered. SH waves only require a scalar treatment, whereas the others require a vector treatment accounting for mode-conversions. Comparisons of predicted attenuation coefficients with experimentally measured ones validate the model.

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