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Austenitic welds and dissimilar welds are extensively used in primary circuit pipes and pressure vessels in nuclear power plants, chemical industries and fossil fuelled power plants because of their high fracture toughness, resistance to corrosion and creep at elevated temperatures. However, cracks may initiate in these weld materials during fabrication process or stress operations in service. Thus, it is very important to evaluate the structural integrity of these materials using highly reliable non- destructive testing (NDT) methods. Ultrasonic non-destructive inspection of austenitic welds and dissimilar weld components is complicated because of anisotropic columnar grain structure leading to beam splitting and beam deflection. Simulation tools play an important role in developing advanced reliable ultrasonic testing (UT) techniques and optimizing experimental parameters for inspection of austenitic welds and dissimilar weld components. The main aim of the thesis is to develop a 3D ray tracing model for quantitative evaluation of ultrasonic wave propagation in an inhomogeneous anisotropic austeniticweld material. Inhomogenity in the anisotropic weld material is represented by discretizing into several homogeneous layers. According to ray tracing model, ultrasonic ray paths are traced during its energy propagation through various discretized layers of the material and at each interface the problem of reflection and transmission is solved. The influence of anisotropy on ultrasonic reflection and transmission behaviour in an anisotropic austenitic weld material are quantitatively analyzed in three dimensions. Theultrasonic beam directivity in columnar grained austenitic steel material is determined three dimensionally using Lamb’s reciprocity theorem. The developed ray tracing model evaluates the transducer excited ultrasonic fields accurately by taking into account the directivity of the transducer, divergence of the ray bundle, density of rays and phase relations as well as transmission coefficients. The ray tracing model is able to determine the ultrasonic wave fields generated by a point source as well as finite dimension array transducers.
In this contribution a 3D ray tracing model for ultrasonic
field evaluation in inhomogeneous anisotropic materials
such as austenitic welds is presented. The inhomogenity of
austenitic weld material is represented as several
homogeneous layers. The general problem of energy
reflection and transmission at the boundaries of the layers
are solved resulting 3D amplitude and energy reflection and
transmission coefficients. The directivity factor for the ray in
general arbitrary oriented austenitic weld material (including
lay back orientation) is determined based on Lambs
reciprocity theorem. The transducer excited ultrasonic fields
are accurately evaluated by employing ray directivity factor,
transmission coefficients, divergence of the ray bundle and
density of rays. Finally, the comparison between theoretical
and experimental results will be described.
In diesem Beitrag wird die numerische Modellierung und deren messtechnische Validierung der elastischen Wellenausbreitung in austenitischen Schweißnähten vorgestellt. Die Ultraschallprüfung von austenitischen Schweißverbindungen war und ist immer noch eine der schwierigsten Aufgaben der ZfP. Für eine optimierte Prüfkonfiguration ist es notwendig, verschiedene Prüfparameter wie Einschallwinkel, Prüfkopfposition und -Orientierung richtig einzustellen. Um die beste Anordnung zu ermitteln, wurde die Schallausbreitung in den austenitischen Schweißnähten mit verschiedenen Verfahren wie elastische finite Integrationstechnik (EFIT) und Raytracing simuliert. Mit Hilfe der Simulationsergebnisse wurde die verwendete Gruppenstrahlerprüftechnik optimiert. Es wurden zahlreiche Untersuchungen an anisotropen Testkörpern in V-Durchschallung und an bezüglich der Schweißnaht transversal orientierten Rissen durchgefühlt. Die Ergebnisse der auf Raytracing bzw. EFIT basierenden Simulationstools wurden untereinander und auch mit den Messergebnissen verglichen.
In this contribution a simulation tool is developed to compute the energy skewing angles and energy coefficients
for the reflected and refracted plane waves in following general cases: (1) reflection and refraction
of plane elastic waves at an interface between isotropic and transversely isotropic solid, (2) reflection
and refraction of plane elastic waves at an interface between transversely isotropic and isotropic solid, (3)
reflection and refraction of plane elastic waves at an interface between two general transversely isotropic
solid and (4) reflection of plane elastic waves from a stress free boundary of a transversely isotropic solid.
Computational results for analytically evaluated acoustic wave energy skewing angles and energy reflection
and transmission coefficients in acoustically anisotropic materials such as austenitic steel materials
exhibiting columnar grain orientation are presented. The obtained results show that the acoustic energy
skewing angles and coefficients in austenitic steel materials strongly depend upon the columnar grain
orientation and are less influenced by the grain orientations which are parallel and perpendicular to the
interface.
This contribution describes a computationally efficient ray tracing algorithm for evaluating transducer generated ultrasonic wave fields in anisotropic materials such as austenitic cladded and austenitic weld components. According to this algorithm, ray paths are traced during its propagation through various layers of the material and at each Interface the problem of reflection and transmission is solved. The presented algorithm evaluates the transducer generated ultrasonic fields accurately by taking in to account the directivity, divergence, density of rays, phase relations as well as transmission coefficients. The ray tracing algorithm is able to calculate the ultrasonic wave fields generated by a point source as well as a finite dimension transducer. The simulation results are compared quantitatively with the results obtained from Elastodynamic Finite Integration Technique (EFIT) on several configurations generally occuring in the ultrasonic non destructive testing of anisotropic materials. The excellent agreement between both models confirms the validity of the presented ray tracing algorithm. Finally, the ray tracing model results are also validated by means of experiments.
For the radiographic investigation of large cargo Containers the energies of conventional Xray tubes are inadequately for certain layer thicknesses. In that case the high energy radiation sources like electron accelerators and gamma radiators (60CO) are adequate for the non invasive inspection of large Containers because of the high penetration through thick materials. Multiple imaging even enables to distinguish between different materials. The main challenging task in air and sea cargo Container inspection is to improve the detectability of contraband and dangerous materials which are hidden in the heterogeneously packed Containers by detailed analysis of cluttered radiographic images. So it is to be expected that objects of organic substances like certain explosives or their precursors are hard to identify behind thick walls of heavy metal objects such as engine-blocks with flat bottom holes. The primary aim here is to investigate the detectability of dangerous materials (typically of light elements) in cargo Containers using high energy X-ray digital radiography.