Modeling ultrasonic structural noise based on the microstructural properties of metals in the context of non destructive evaluation NDCM 2013 V. Dorval, L. Ducousso-Ganjehi, S. Chatillon, F. Jenson

Thickness of large bands: 5 to 8 mm APPLICATION CASES Focus on Complex Nuclear componentS Pressurizer Steam generator Pump Reactor Nuclear power plant Cast Stainless Steel (CASS) components 20 mm 1 mm O.D. I.D. Thickness of large bands: 5 to 8 mm 2013 International Congress on Ultrasonics | V. Dorval, L. Ducousso-Ganjehi, S. Chatillon, F. Jenson

APPLICATION CASES Focus on Complex AERONAUTIC componentS Superalloys turbine blades 2013 International Congress on Ultrasonics | V. Dorval, L. Ducousso-Ganjehi, S. Chatillon, F. Jenson

Structural noise Structural noise and attenuation x t NON DESTRUCTIVE TESTING OF COMPLEX MATERIALS Homogeneous medium t x Scattering medium A part of the energy is scattered in all direction by the microstructure Structural noise and attenuation These phenomena can cause significant loss in ultrasonic non destructive evaluation of highly scattering materials. 2013 International Congress on Ultrasonics | V. Dorval, L. Ducousso-Ganjehi, S. Chatillon, F. Jenson

Longitudinal waves in Ti alloy EXAMPLE: UT NOISE IN TITANIUM ALLOY BILLETS Measurement setup Focused transducer Focal length F = 406.2 mm Diameter = 25.4 mm Center frequency f0 = 10 MHz Immersion Normal incidence The waterpath was chosen such that the beam was focused in the half depth of the block 70 mm 2013 International Congress on Ultrasonics | V. Dorval, L. Ducousso-Ganjehi, S. Chatillon, F. Jenson

Longitudinal waves in Ti alloy UT NOISE IN TITANIUM ALLOY BILLETS Cscan 1- Cscan 2- Bscan Envelopes of the signal are measured for each probe position Envelopes are averaged over probe positions Expressed in dBs compared to the amplitude of the echo of a reference FBH echo 3- Mean noise level 2013 International Congress on Ultrasonics | V. Dorval, L. Ducousso-Ganjehi, S. Chatillon, F. Jenson

Longitudinal waves in Ti alloy UT NOISE IN TITANIUM ALLOY BILLETS Biphasic structure with elongated macrograins 70 mm Ti alloy Time (µs) Z205 Face Z1 Face Z1 Mean noise level (dB) Face R1 Macrograph Micrograph Biphasic structure with equiaxed macrograins Biphasic structure with elongated macrograins Z205 Face R1 Noise level anisotropy depends strongly on the metallurgical structure 2013 International Congress on Ultrasonics | V. Dorval, L. Ducousso-Ganjehi, S. Chatillon, F. Jenson

Structural noise Simulation Origin of the phenomenon In case of a monophasic medium, scattering is due to acoustic impedance fluctuations of grains Mono-phasic medium, random, homogeneous and isotropic (statistically) Single scattering (Born approximation) Plane wave(far field) with Spatial correlation function: Shape and size of grains Elastic constants variation In case of LL and θ = 180° 2013 International Congress on Ultrasonics | V. Dorval, L. Ducousso-Ganjehi, S. Chatillon, F. Jenson

Structural noise Simulation Origin of the phenomenon In case of biphasic medium, scattering is due to acoustic impedance fluctuations of grains and contrast between phases Random crystallographic orientation of macrograins Crystallographic orientation relationships between phases: each variant occurs with equal probability Individual crystallites are too small to make a significant contribution to the grain noise In case of LL and θ = 180° Averaged over all colonies orientation Averaged over all macrograins orientation 2013 International Congress on Ultrasonics | V. Dorval, L. Ducousso-Ganjehi, S. Chatillon, F. Jenson

Structural noise Simulation Backscattering coefficient Higher scattering coefficients are obtained for transverse waves than for longitudinal waves. In both cases, the backscattering coefficient for two phases case has a frequency dependency similar to the macrograin coefficient for low frequencies and to the colonies coefficient for the higher frequencies. It confirms that it is necessary to take into account both scales of the material structure in order to be able to properly model the scattering at all frequencies. 2013 International Congress on Ultrasonics | V. Dorval, L. Ducousso-Ganjehi, S. Chatillon, F. Jenson

Structural noise Simulation Attenuation coefficient For both L and T waves, the attenuation coefficient for the two-phases structure is somewhere inbetween the attenuation for macrograins and that for colonies. For the case of L waves, it is very close to the attenuation due to colonies, but this is not a general behavior, as it is strongly dependent on the material properties . L T 2013 International Congress on Ultrasonics | V. Dorval, L. Ducousso-Ganjehi, S. Chatillon, F. Jenson

Structural noise Simulation Summary of the computation method (see presentation LUT-10 Session D5 – Laser ultrasound – Thursday at 5:40 PM) Determination of a sufficient number of scatterers Properties of the microstructure Scattering coefficient Computation of the emission and the reception by the probe Distribution of scatterers Properties of the probe and the part Input parameters Objective: To predict the influence of the metallic alloys microstructure on the inspection performances Time Position Simulated B-Scan 2013 International Congress on Ultrasonics | V. Dorval, L. Ducousso-Ganjehi, S. Chatillon, F. Jenson

Longitudinal waves in Ti alloy COMPARISONS BETWEEN EXPERIMENTAL AND NUMERICAL RESULTS TI ALLOY Experimental result CIVA result Face R1 - Biphasic structure - Ellipsoidal macrograin = 100 µm with L/l = 5.5 Colony = 25 µm Elastic constants (bibliography) Face R1 Experimental result CIVA result Face Z1 - Biphasic structure - Equiaxed Macrograin = 100 µm Colony = 2 µm Elastic constants (bibliography) Face Z1 Very good agreement between experimental and CIVA results 2013 International Congress on Ultrasonics | V. Dorval, L. Ducousso-Ganjehi, S. Chatillon, F. Jenson

Longitudinal waves in steel alloy COMPARISONS BETWEEN EXPERIMENTAL AND NUMERICAL RESULTS Input data in CIVA software Elastic constants of biphasic medium Percentage of colony 85 % Macrograin size 4 mm Colony size 1 mm Macrograin shape Equiaxe Colony shape Equiaxe (?) STEEL ALLOY 2013 International Congress on Ultrasonics | V. Dorval, L. Ducousso-Ganjehi, S. Chatillon, F. Jenson

SHEAR waves in steel alloy shear waves in small grain austenitic steel Time Time Inspection with shear wave at 45° at 2.25MHz on a sample of austenitic steel with ≈120μm grains Position Position Measured B-Scan Simulated B-Scan Comparison of noise levels by plotting the average envelope as a function of time Evolution of the noise correctly simulated, but underestimation by 5 dBs Constructive interferences near the backwall of the part are correctly simulated 2013 International Congress on Ultrasonics | V. Dorval, L. Ducousso-Ganjehi, S. Chatillon, F. Jenson

Limitations of the method: Multiple scattering not taken into account Conclusion Structural noise can be simulated using a random distribution of scatterers with properties that are related to properties of the microstructure Correct prediction of the evolution of the noise level in several cases (Titanium and steel alloys) Limitations of the method: Multiple scattering not taken into account Underestimation of the noise for austenitic steel inspected with shear waves Perspectives Simulation of multiple scattering (presentation concerning the work of T. Bedetti) Amelioration of the accuracy of the simulation: Possible explanation for the underestimation for austenitic steel with shear waves: inaccuracy of the Born approximation due to the important variations of elastic properties in this material with shear waves Development of a more accurate scattering model in the SIMPOSIUM European project with IZFP (S. Hirsekorn) Experimental Determination of elastic properties in collaboration with LAUM (Session D5 at 5:40 PM) 2013 International Congress on Ultrasonics | V. Dorval, L. Ducousso-Ganjehi, S. Chatillon, F. Jenson

Thank you for your attention lili.ganjehi@cea.fr 2013 International Congress on Ultrasonics | V. Dorval, L. Ducousso-Ganjehi, S. Chatillon, F. Jenson