TY - JOUR A1 - Gravenkamp, Hauke A1 - Song, C. A1 - Prager, Jens T1 - A numerical approach for the computation of dispersion relations for plate structures using the scaled boundary finite element method N2 - In this paper, a method is presented for the numerical computation of dispersion properties and mode shapes of guided waves in plate structures. The formulation is based on the Scaled Boundary Finite Element Method. The through-thickness direction of the plate is discretized in the finite element sense, while the direction of propagation is described analytically. This leads to a standard eigenvalue problem for the calculation of wave numbers. The proposed method is not limited to homogeneous plates. Multi-layered composites as well as structures with continuously varying material parameters in the direction of thickness can be modeled without essential changes in the formulation. Higher-order elements have been employed for the finite element discretization, leading to excellent convergence for complex structures. It is shown by numerical examples that this method provides highly accurate results with a small number of nodes while avoiding numerical problems and instabilities. KW - Scaled boundary finite element method KW - Lamb waves KW - Dispersion KW - Non-destructive testing KW - Composites KW - Functionally graded materials PY - 2012 U6 - https://doi.org/10.1016/j.jsv.2012.01.029 SN - 0022-460X SN - 1095-8568 VL - 331 IS - 11 SP - 2543 EP - 2557 PB - Academic Press CY - London AN - OPUS4-25743 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Rahman, Mehbub-Ur A1 - Prager, Jens T1 - Simulation of lamb wave propagation with elastodynamic finite integration technique (EFIT) N2 - 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. T2 - DAGA 2012 - 38. Jahrestagung für Akustik - Fortschritte der Akustik CY - Darmstadt, Deutschland DA - 2012-03-19 PY - 2012 SP - 953 EP - 954 PB - Deutsche Gesellschaft für Akustik e.V. AN - OPUS4-25999 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Rahman, Mehbub-Ur A1 - Prager, Jens ED - Linde, B. B. J. ED - Paczkowski, J. ED - Ponikwicki, N. T1 - Modeling of lamb wave propagation with elastodynamic finite integration technique N2 - This paper presents the numerical modeling of the Lamb wave propagation in thin plates 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 such as the finite integration technique (FIT), the finite element method (FEM) and the boundary element method (BEM) can be used to model this NDT situation. The elastodynamic finite integration technique (EFIT) is an effective tool to model Lamb wave propagation in plates over long distances in an efficient way. With the help of the simulation results obtained from the EFIT tool the propagation of different symmetric and anti-symmetric 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 analytical results is also presented. T2 - International congress on ultrasonics CY - Gdansk, Poland DA - 2011-09-05 KW - NDT KW - EFIT KW - Lamb wave KW - Symmetric and anti-symmetric modes PY - 2012 SN - 978-0-7354-1019-0 U6 - https://doi.org/10.1063/1.3703226 SN - 0094-243X N1 - Serientitel: AIP conference proceedings – Series title: AIP conference proceedings IS - 1433 SP - 455 EP - 458 PB - American Institute of Physics CY - Melville, NY AN - OPUS4-26202 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Gravenkamp, Hauke A1 - Saputra, A. A. A1 - Song, C. A1 - Prager, Jens ED - Linde, B. B. J. ED - Paczkowski, J. ED - Ponikwicki, N. T1 - Detection of defects in thin-walled structures by means of lamb waves N2 - In this paper the Scaled Boundary Finite Element Method (SBFEM) is applied for the simulation of Lamb waves in cracked plates. This method is highly advantageous to study the interaction of different Lamb wave modes with cracks as the crack is not discretized and no refinement is required around the crack tip. Numerical examples are presented for the reflection of the fundamental symmetric and antisymmetric modes from cracks of different depth. The spatial Fourier transformation is employed to calculate the amplitudes of reflected Lamb wave modes. The results reveal possibilities to obtain details of the crack geometry in non-destructive testing and structural health monitoring applications. T2 - International congress on ultrasonics CY - Gdansk, Poland DA - 05.09.2011 KW - Lamb waves KW - Scaled boundary finite element method KW - Simulation KW - Crack detection PY - 2012 SN - 978-0-7354-1019-0 U6 - https://doi.org/10.1063/1.3703223 SN - 0094-243X N1 - Serientitel: AIP conference proceedings – Series title: AIP conference proceedings IS - 1433 SP - 443 EP - 446 PB - American Institute of Physics CY - Melville, NY AN - OPUS4-26203 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Kolkoori, Sanjeevareddy A1 - Rahman, Mehbub-Ur A1 - Prager, Jens T1 - 3D ray tracing model for ultrasound field evaluation in inhomogeneous anisotropic materials: model and experimental validation N2 - 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 Lamb’s 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. T2 - DAGA 2012 - 38. Jahrestagung für Akustik - Fortschritte der Akustik CY - Darmstadt, Deutschland DA - 2012-03-19 KW - Ultrasonic field KW - 3D ray tracing KW - Inhomogeneous KW - Austenitic weld PY - 2012 SP - 959 EP - 960 PB - Deutsche Gesellschaft für Akustik e.V. AN - OPUS4-26204 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Kolkoori, Sanjeevareddy A1 - Rahman, Mehbub-Ur A1 - Chinta, P.K. A1 - Kreutzbruck, Marc A1 - Prager, Jens ED - Thompson, D. O. ED - Chimenti, D. E. T1 - Quantitative evaluation of ultrasonic sound fields in anisotropic austenitic welds using 2D ray tracing model N2 - Ultrasonic investigation of inhomogeneous anisotropic materials such as austenitic welds is complicated because its columnar grain structure leads to curved energy paths, beam splitting and asymmetrical beam profiles. A ray tracing model has potential advantage in analyzing the ultrasonic sound field propagation and there with optimizing the inspection parameters. In this contribution we present a 2D ray tracing model to predict energy ray paths, ray amplitudes and travel times for the three wave modes quasi longitudinal, quasi shear vertical, and shear horizontal waves in austenitic weld materials. Inhomogenity in the austenitic weld material is represented by discretizing the inhomogeneous region into several homogeneous layers. At each interface between the layers the reflection and transmission problem is computed and yields energy direction, amplitude and energy coefficients. The ray amplitudes are computed accurately by taking into account directivity, divergence and density of rays, phase relations as well as transmission coefficients. Ultrasonic sound fields obtained from the ray tracing model are compared quantitatively with the 2D Elastodynamic Finite Integration Technique (EFIT). The excellent agreement between both models confirms the validity of the presented ray tracing results. Experiments are conducted on austenitic weld samples with longitudinal beam transducer as transmitting probe and amplitudes at the rear surface are scanned by means of electrodynamical probes. Finally, the ray tracing model results are also validated through the experiments. T2 - 38th Annual Review of Progress in Quantitative Nondestructive Evaluation CY - Burlington, VT, USA DA - 2011-07-17 KW - Ultrasonic sound field KW - Ray tracing KW - Ray directivity KW - Austenitic weld PY - 2012 SN - 978-0-7354-1013-8 U6 - https://doi.org/10.1063/1.4716359 SN - 0743-0760 SN - 0094-243X N1 - Serientitel: AIP conference proceedings – Series title: AIP conference proceedings IS - 1430 SP - 1227 EP - 1234 PB - American Institute of Physics CY - Melville, NY AN - OPUS4-26205 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Kolkoori, Sanjeevareddy A1 - Rahman, Mehbub-Ur A1 - Chinta, P.K. A1 - Boehm, Rainer A1 - Prager, Jens ED - Linde, B. B. J. ED - Paczkowski, J. ED - Ponikwicki, N. T1 - Simulation of ultrasonic fields in anisotropic materials using 2D ray tracing method N2 - Ultrasound propagation in inhomogeneous anisotropic materials is difficult to examine because of the directional dependency of elastic properties. Simulation tools play an important role in developing advanced reliable ultrasonic testing techniques for the inspection of anisotropic materials particularly austenitic cladded materials and dissimilar welds. A 2-D Ray tracing method is developed for evaluating ray path, amplitude and travel time for three wave modes namely quasi longitudinal wave (qP), quasi shear vertical wave (qSV) and shear horizontal waves (SH) in anisotropic materials such as austenitic cladded materials. The inhomogenity in the anisotropic material is represented by discretizing the anisotropic region into several homogeneous layers. The ray paths are traced during its propagation through the various interfaces between those layers. At each interface the problem of reflection and refraction is solved. The ray amplitudes are computed by taking into account the directivity and phase relations. Ray divergence variation and ray transmission coefficients at each refraction boundary are considered. The Ray tracing results for ultrasonic field profiles in austenitic cladded materials are validated quantitatively by 2-D Elastodynamic Finite Integration Technique (EFIT) results and by the experiments. T2 - International congress on ultrasonics CY - Gdansk, Poland DA - 2011-09-05 KW - Ray path KW - Energy vector KW - Austenitic cladded material KW - Ultrasonic beam profile PY - 2012 SN - 978-0-7354-1019-0 U6 - https://doi.org/10.1063/1.3703288 SN - 0094-243X N1 - Serientitel: AIP conference proceedings – Series title: AIP conference proceedings IS - 1433 SP - 743 EP - 746 PB - American Institute of Physics CY - Melville, NY AN - OPUS4-26207 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Kreutzbruck, Marc A1 - Prager, Jens A1 - Boehm, Rainer A1 - Kitze, Jessica A1 - Brekow, Gerhard T1 - Progress in acoustical defect sizing NDT methods for the inspection of power-plant components N2 - 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). T2 - 18th WCNDT - World conference on nondestructive testing CY - Durban, South Africa DA - 2012-04-16 KW - SAFT KW - TOFD KW - Cracks KW - Phased Array PY - 2012 SN - 978-0-620-52872-6 SP - 1 EP - 8 (Paper 497) AN - OPUS4-26350 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Höhne, Christian A1 - Boehm, Rainer A1 - Prager, Jens T1 - Application of 2-dimensional analytic signals with single-quadrant spectra for processing of SAFT-reconstructed images N2 - The Synthetic Aperture Focusing Technique (SAFT) is an algorithm applied in non-destructive ultrasonic testing which provides an image of flaws within a specimen. The image is reconstructed from A-scans measured at different positions. Reliable evaluation of the images obtained by the SAFT-algorithm, however, depends on the representation of the reconstructed data, which is initially given in terms of positive and negative local values only. A suitable way of processing this data for evaluation is to calculate the envelope, which can be achieved by means of the analytic signal. The extension of this concept to the multidimensional case is neither trivial nor unique and although extensive work on this subject has been carried out in the past, a correct envelope calculation in multidimensional data remains difficult since it depends on an additional condition, namely the separability of the signal. In this paper, the concept of analytic signals with single-quadrant spectra is applied to process 2-dimensional data obtained by the SAFT-algorithm. Furthermore, we present a procedure to overcome the limitations of that approach by selecting local magnitude values from a number of rotated frames after evaluating the signal’s separability in each frame, which is briefly validated against synthetic and experimental data. KW - Analytic signal KW - Complex signal KW - Image processing KW - SAFT image PY - 2014 U6 - https://doi.org/10.1007/s11045-013-0226-7 SN - 0923-6082 SN - 1573-0824 VL - 25 IS - 4 SP - 703 EP - 722 PB - Kluwer CY - Boston, Mass. [u.a.] AN - OPUS4-28606 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Gravenkamp, Hauke A1 - Man, H. A1 - Song, C. A1 - Prager, Jens T1 - The computation of dispersion relations for three-dimensional elastic waveguides using the scaled boundary finite element method N2 - In this paper, a numerical approach for the computation of dispersion relations for three-dimensional waveguides with arbitrary cross-section is proposed. The formulation is based on the Scaled Boundary Finite Element Method (SBFEM). It is an extension of the approach previously derived for plate structures. It is shown that the wavenumbers of guided waves in a waveguide can be obtained as the eigenvalues of the Z matrix, which is well known in the SBFEM. The Hamiltonian properties of this matrix are utilized to derive an efficient way to compute the group velocities of propagating waves as eigenvalue derivatives. The cross-section of the waveguide is discretized using higher-order spectral elements. It is discussed in detail how symmetry axes can be utilized to reduce computational costs. In order to sort the solutions at different frequencies, a mode-tracking algorithm is proposed, based on the Padé expansion. KW - Guided waves KW - Simulation KW - Dispersion KW - Scaled boundary finite element method PY - 2013 U6 - https://doi.org/10.1016/j.jsv.2013.02.007 SN - 0022-460X SN - 1095-8568 VL - 332 IS - 15 SP - 3756 EP - 3771 PB - Academic Press CY - London AN - OPUS4-28837 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -