Ultrasonic guided wave inspection is expanding rapidly to many different areas of manufacturing and in-service inspection. The purpose of this paper is to provide a vision of ultrasonic guided wave inspection potential aswe move forward into the new millennium. An increased understanding of the basic physics and wave mechanics associated with guided wave inspection has led to an increase in practical nondestructive evaluation and inspection problems. Some fundamental concepts and a number of different applications that are currently being considered will be presented in the paper along with a brief description of the sensor and software technology that will make ultrasonic guided wave inspection commonplace in the next century.

A Baseline and Vision of Ultrasonic Guided Wave Inspection Potential

Defect detection in pipes using guided waves

Modeling wave propagation in damped waveguides of arbitrary cross-section

Review of progress, QNDE

Guided acoustic and ultrasonic waves have been utilized in various manners for non-destructive evaluation and testing. If a guided wave mode is dispersive, a pulse of energy will spread out in space and time as it propagates. For a long-range guided wave inspection application, this constrains the choice of operating point to regions on the dispersion curves where dispersion effects are small. A signal processing technique is presented that enables this constraint on operating point to be relaxed. The technique makes use of a priori knowledge of the dispersion characteristics of a guided wave mode to map signals from the time to distance domains. In the mapping process, dispersed signals are compressed to their original shape. The theoretical basis of the technique is described and an efficient numerical implementation is presented. The robustness of the technique to inaccuracies in the dispersion data is also addressed. The application of the technique to experimental data is shown and the resulting improvement in spatial resolution is demonstrated. The implications of using dispersion compensation in practical systems are briefly discussed.

A rapid signal processing technique to remove the effect of dispersion from guided wave signals

The application of guided waves in NDT can be hampered by the lack of readily available dispersion curves for complex structures. To overcome this hindrance, we have developed a general purpose program that can create dispersion curves for a very wide range of systems and then effectively communicate the information contained within those curves. The program uses the global matrix method to handle multi-layered Cartesian and cylindrical systems. The solution routines cover both leaky and non-leaky cases and remain robust for systems which are known to be difficult, such as large frequency-thicknesses and thin layers embedded in much thicker layers. Elastic and visco-elastic isotropic materials are fully supported; anisotropic materials are also covered, but are currently limited to the elastic, non-leaky, Cartesian case.

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=3475&context=qnde

Disperse: a general purpose program for creating dispersion curves

The dispersion relationships of a system comprising a circular bar imbedded in a solid medium having a lower acoustic impedance than the bar have been predicted. A generic study of such systems has been undertaken, motivated by a particular interest in the case of a circular steel bar imbedded in cement grout which has application to the inspection of tendons in post-tensioned concrete bridges; measurements to confirm the predictions have been carried out for this case. The attenuation dispersion curves show a series of attenuation minima at roughly equal frequency spacing. The attenuation minima occur at the same frequencies as energy velocity maxima and they correspond to points at which the particle displacements and energy of the particular mode are concentrated towards the center of the bar so leakage of energy into the imbedding medium is minimized. The attenuation at the minima decreases with increasing frequency as the energy becomes more concentrated at the middle of the bar, until the material attenuation in the bar becomes a significant factor and the attenuation at the minima rises again. For the particular case of a steel bar in cement grout, the minimum attenuation is reached at a frequency-radius product of about 23 MHz-mm. The frequency-radius product at which the minimum attenuation is reached and the value of the minimum attenuation both increase as the acoustic impedance of the imbedding medium increases.

High-Frequency Low-Loss Ultrasonic Modes in Imbedded Bars

Guided wave inspection has a number of advantages over conventional ultrasonic inspection. For instance, guided waves can propagate over many tens of metres in rail, they can fully penetrate alumino-thermic welds and theyare very sensitive to cracks in the transverse-vertical plane that may cause catastrophic failure. With financial and technical support from Network Rail, the authors are developing a guided wave inspection system for rail, which is described in this paper. Experimental and finite element results showing the interaction of various guided wave modes with a wide variety of defect geometries are presented. This study has enabled characteristic mode conversion signatures for various defects and features to be obtained and these signatures will provide the basis for an automatic feature extraction algorithm. Results from laboratory tests and site trials are presented that demonstrate the ability of the system to detect a range of defects in free rail, aluminio-thermic welds and in rail at a level crossing.

Guided wave testing of rail

Ultrasonic techniques have been used for many years for the inspection of rail. These measurements can detect the presence of a wide variety of defects but there are practical difficulties with the technology. While large transverse cracks of the type likely to cause catastrophic failure can be detected, the large, critical defects can be masked by large numbers of small, surface defects along the length of the rail. It would be very useful to be able to determine reliably the largest defect size in a length of rail. Also alumino-thermic welds are difficult to inspect due to the typical defect orientation and the attenuation of the weld material. Guided waves provide a very attractive solution to these problems; they travel along the rail, for tens or hundreds of metres, and are partially reflected by any defects which are present. They are particularly sensitive to vertical defects and they are used at relatively low frequency so they are not significantly attenuated by weld material. With financial support from Network Rail, the authors have developed a practical inspection tool based on guided wave measurements. This paper describes the design of a pre-production prototype guided wave instrument suitable for site trials. Results obtained at a level crossing are presented that demonstrate the use of the system as a practical screening tool. For the covering abstract see ITRD E123761.

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Long range inspection of rail using guided waves - field experience

Low frequency guided acoustic waves will propagate many tens of metres along a rail The guided wave modes that can exist in a rail are found using a 2‐dimensional finite element (FE) technique and their interaction with a variety of features and defects is investigated with 3‐dimensional time‐marching FE models Results obtained from a prototype testing system are presented and excellent agreement is obtained with FE predictions Good sensitivity to transverse defects and defects at alumino‐thermic welds is demonstrated

Brian Pavlakovic

Papers

Disperse: a general purpose program for creating dispersion curves

High-Frequency Low-Loss Ultrasonic Modes in Imbedded Bars

Guided wave testing of rail

Long range inspection of rail using guided waves - field experience

Long Range Inspection of Rail Using Guided Waves