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This paper presents the numerical modeling of the Lamb
wave propagation in plate like structures with the
Elastodynamic Finite Integration Technique (EFIT) and its
validation with the measured results. In general, Lamb
waves offer an attractive method to detect the defects inside
long plate like structures efficiently. However, such a nondestructive
testing (NDT) requires profound understanding
of the Lamb wave propagation in the plates, generation of
the symmetric and anti-symmetric modes of different orders
and their interaction with the defects of the materials.
Modern simulation tools based on numerical methods can be
used to model this complex NDT situation. EFIT is an
effective tool to model such problems in an efficient way.
With the help of the simulation results obtained from the
EFIT tool the propagation of different symmetric and antisymmetric
Lamb wave modes is analyzed and thus a proper
technique is developed to excite different modes and to
separate them from each other precisely. A validation of the
numerical results with the measured results is also presented.
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.
Progress in acoustical defect sizing NDT methods for the inspection of power-plant components
(2012)
The demand of improved NDT methods with proper visualization and sizing
capabilities is a persistent trend in maintenance and manufacturing quality inspection.
Especially when dealing with high quality standards in conjunction with safety-critical
components in the sector of energy and transportation quantitative NDT techniques are
vital to provide reliable quality control systems and a corresponding deeper insight into
the component structure for a further fracture-mechanical estimation. The paper thus
focuses the progress of the defect sizing capabilities of modern Ultrasonic Testing
(UT). In Ultrasonic Testing the SAFT-algorithm (Synthetic Aperture Focusing
Technique) currently experiences a renaissance. The method is based on combining the
data of different transducer positions with their corresponding varied propagating time
and it is currently applied in several industrial applications. SAFT enhances the SNR
and the spatial resolution and is thus a valuable tool when it comes to improved
defect detection and sizing. A tomographic-like data mapping is illustrated on several
examples, where adapted phased array systems were used for the inspection of turbine
components and also for a cladded mock-up of a nuclear reactor pressure vessel. In a
statistical investigation we also performed a comparison with other defect sizing
methods like TOFD (Time of flight diffraction).
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.
In this paper a numerical approach, based on the Scaled Boundary Finite Element Method (SBFEM), is described to obtain dispersion relations for propagating modes in wave guides. While the formulation is developed for plate structures, it can easily be extended to wave guides with arbitrary cross-section. The cross-section is discretized in the Finite Element sense while all equations remain analytical in the direction of propagation. The wave numbers of all propagating modes are obtained as the solutions of a standard eigenvalue problem. The group velocities can be calculated accurately as the eigenvalue derivatives. The use of higher-order elements drastically increases the efficiency and accuracy of the computation. This approach can be used for wave guides with arbitrary distribution of material parameters.
In non-destructive testing and structural health monitoring with ultrasonic waves, the quantification of damage in components is one of the main tasks. In many shell-like structures, such as plates, pipes, or laminate components, ultrasonic waves propagate as guided waves. Although guided waves enable the testing of large areas, their multimodal and dispersive properties make it challenging to analyze signals. So, there is a need for more advanced algorithms to handle these properties, especially when reconstructing damage position and geometry.
The reconstruction can be formulated as an inverse problem where the measured signals are fitted with a simulative forward model. Due to the small wavelength of ultrasonic waves, classic forward models based on, e.g., the Finite Element Method are computationally intensive. In contrast, the authors use the semi-analytical Scaled Boundary Finite Element Method (SBFEM) to reduce the computational effort. The SBFEM approximates arbitrary long, undamaged parts of the structure with only a few degrees of freedom.
This contribution summarizes a general inverse procedure based on algorithmic differentiation in combination with the SBFEM. Results are presented for damaged 2D cross-sectional models of waveguides. These results include an analysis of the robustness of the proposed algorithms against noise.
In the field of non-destructive testing, Lamb waves are often used for material characterisation. The increasing computational capabilities further enable complex and detailed simulations to predict the material behaviour in reality. Since adhesive bonding of different materials is a widely used method in modern applications, a reliable measurement system to determine the quality of these adhesive bonds is needed. Investigations of the dispersive behaviour of acoustic waves in adhesively bonded multi-layered waveguides show mode repulsions in the dispersion diagrams in regions where the modes of the single materials would otherwise intersect. In previous works, changes of the distance between those modes with respect to the bonding quality are observed. The experimental data for this investigation is generated using pulsed laser radiation to excite broadband acoustic waves in plate like specimens which are detected by a piezoelectric ultrasonic transducer. Numerical data is generated using simulations via a semi-analytical finite element method. Using a combination of experimental and numerical data, the present work introduces an approach to determine a parameter which indicates the bonding quality in relation
to an ideal material coupling.
In the context of Industry 4.0 and especially in the field of Structural Health Monitoring, Condition Monitoring and Digital Twins, simulations are becoming more and more important. The exact determination of material parameters is required for realistic results of numerical simulations of the static and dynamic behavior of technical structures. There are many possibilities to determine
elastic material parameters. One possibility of non-destructive testing are ultrasonic guided waves. For the evaluation of the measurement results, mostly inverse methods are applied in order to be able to draw conclusions about the elastic material parameters from analysing the ultrasonic guided wave propagation. For the inverse determination of the elastic material Parameters with ultrasonic guided waves, several investigations were carried out, e.g. the determination of the isotropic material parameters through the point of zero-groupvelocity or anisotropic material parameters with a simplex algorithm. These investigations are based on the evaluation of dispersion images. Machine learning and in particular Convolutional Neural Networks (CNN) are one possibility of the automated evaluation from Image data, e.g. classification or object recognition problems. This article shows how the dispersive behavior of ultrasonic guided waves and CNNs can be used to determine the isotropic elastic constants of plate-like structures.