Won-Joon Song

Guided wave dispersion curves for a bar with an arbitrary cross-section, a rod and rail example

Theoretical and experimental issues of acquiring dispersion curves for bars of arbitrary cross-section are discussed. Since a guided wave can propagate over long distances in a structure, guided waves have great potential for being applied to the rapid non-destructive evaluation of large structures such as rails in the railroad industry. Such fundamental data as phase velocity, group velocity, and wave structure for each guided wave mode is presented for structures with complicated cross-sectional geometries as rail. Phase velocity and group velocity dispersion curves are obtained for bars with an arbitrary cross-section using a semi-analytical finite element method. Since a large number of propagating modes with close phase velocities exist, dispersion curves consisting of only dominant modes are obtained by calculating the displacement at a received point for each mode. These theoretical dispersion curves agree in characteristic parts with the experimental dispersion curves obtained by a two-dimensional Fourier transform technique.

Ultrasonic guided wave scattering in a plate overlap

Guided wave scattering in a plate overlap is investigated by numerical calculations and experimental measurements of transmission and reflection factors from the overlap region. In the numerical study, a hybrid boundary element-finite element method is used to calculate the guided wave scattered field from the overlap region. Transmission and reflection factors are calculated for incident A0 and S0 Lamb and n0 shear horizontal waves, including higher modes generated through mode conversion phenomena. In addition, parametric studies of transmission and reflection factors in this problem are performed numerically over various incident modes, frequencies, and overlap lengths. For verification and comparison with numerical results, experiments were conducted to measure the transmission and reflection factors for incident Lamb and shear horizontal waves in steel plates with two different overlap areas. The experimental results agree well with the numerical calculations. The numerical and experimental results show that it is highly feasible to carry out efficient Lamb wave nondestructive evaluation (NDE) in overlapped plates and in multilayer structures with various lap joints by selecting various modes and tuning frequency.

Transmission and Reflection of A0 Mode Lamb Wave in a Plate Overlap

Lamb wave propagation in a plate overlap is investigated. Transmission and reflection coefficients for incident Lamb waves of A0 mode across the overlap region are numerically calculated using a hybrid BE‐FE method. Transmission and reflection coefficients of the Lamb wave across the overlap region are studied as a function of frequency and overlap length. In addition, mode conversion phenomena from the incident waves within the overlap region are also included in the numerical study. A few experiments were also conducted for measurements of transmission and reflection coefficients for incident A0 mode wave in overlap‐shaped steel plates with two different overlap areas. The experimental results are in good agreement with the numerical calculations. The numerical and experimental results can be used to establish guidelines for NDE in overlapped plates and in multilayer structures with various joints by selecting modes and tuning frequency.

Non‐Axisymmetric Wave Focusing in Pipe Inspection

Non‐axisymmetric guided waves have been applied to pipe inspection recently. Due to the non‐axisymmetric characteristics of the waves, the circumferential displacement distribution is non‐axisymmetric. It shows a natural focusing phenomenon. With the aid of a circumferential transducer array, we developed an algorithm to focus wave energy at arbitrary locations. The algorithm is based on applying different amplitude and time delay to each of the excitation elements. A series of experiments were carried out to show the focusing effect.

Detection of damage in a ship hull using ultrasonic guided waves

A technique to detect damage in a ship hull using guided waves is presented. An approximate image of damage (Defect Locus Map) is produced using guided waves. Damage location and size are determined based on Defect Locus Map. In the experiments, shear horizontal waves and Lamb waves are used and the experimental results are compared. The potential of the Defect Locus Map technique to detect and quantify damage in a ship hull is discussed.

Development of Calculation Software for Guided Wave Propagation In a Pipe

Pipe screening technique with guided waves has become widely applied to pipe inspection in actual industrial plants. In most cases, however, guided wave propagating in a pipe is still difficult for inspection technicians due to its complex characteristics. Authors have developed the fast calculation technique for guided wave propagation using a semi‐analytical finite element method (SAFEM). This study is on development of software for guided wave propagation with the SAFE calculation. A parameter input interface was made with Visual C++, and a core execution file was coded with Fortran 90. Visualization of data set obtained by the calculation was carried out with a free visualization tool OPEN DX. Using this software including a preprocessor and a postprocessor, many kinds of guided wave simulation have become feasible even by a non‐expert in guided waves.

Evaluation of Thickness Reduction in a Thin Plate Using a Non‐Contact Guided Wave Technique

Ultrasonic guided waves are widely being studied and successfully applied to various non‐destructive tests with the advantage of a long range inspection. Recently, non‐contact methods are also adopted and combined with the guided wave techniques. In this paper, an advanced technique for the nondestructive detection of thinning defects simulating hidden corrosion in thin plates using non‐contact guided waves is presented. The proposed approach uses EMAT(Electro‐Magnetic Acoustic Transducer) for the non‐contact generation and detection of guided plate waves in aluminum plates. Interesting features of the dispersive behavior in selected wave modes are used for the detection of plate thinning. The experimental results show that the mode cutoff measurements provide a qualitative measurement of thinning defects and change in the mode group velocity can be used as quantitative parameter of thinning depth measurement.