Lamb waves have shown great potential for structural health monitoring The technique is based on guided ultrasonic waves introduced into a structure at one point and sensed at a different location Damage in a structure is identified by a change in the output signal However, previous studies show that even simple structural configurations can lead to complex response signals Therefore a knowledge and understanding of wave propagation can ease the interpretation of damage detection results This paper reports an application of the local interaction simulation approach for Lamb wave propagation modelling in metallic structures The focus of the analysis is on two-dimensional wave interactions with slot-type defects The method shows the potential for complex modelling of acousto-ultrasonic waves in damage detection applications

https://iopscience.iop.org/article/10.1088/0964-1726/12/5/019/pdf

Modelling of Lamb waves for damage detection in metallic structures: Part II. Wave interactions with damage

3-D seismic response analysis of long lined tunnels in half-space

An up to date literature survey on the dynamics of underground structures is presented briefly. The dynamic response of large three-dimensional underground structures to external or internal dynamic forces or to seismic waves is numerically determined by the frequency domain boundary element method. This method is used to model both the structure and the soil medium, which are assumed to behave as linear elastic or viscoelastic bodies. The full-space dynamic fundamental solution is employed in the formulation and this requires a free soil surface discretization, confined to a finite portion around the area of interest, in addition to soil—structure interface and free structural surface discretizations. The dynamic disturbances can have a harmonic or a transient time variation. The transient case is treated with the aid of numerical Laplace transforms with respect to time. Various numerical examples involving lined cavities and long lined tunnels buried in the full- or the half-space subjected to harmonic or transient external forces or seismic waves are presented to illustrate the method and demonstrate its advantages.

Dynamic analysis of large 3-D underground structures by the bem

Maintenance of air, land and sea structures is an important engineering activity in a wide range of industries including transportation and Civil Engineering. Effective maintenance minimises not only the cost of ownership of structures but also improves safety and the perception of safety. Inspection for material/structural damage, such as fatigue cracks and corrosion in metallics or delamination in composites, is an essential part of maintenance.

Structural Health Monitoring Using Guided Ultrasonic Waves

Wave propagation modelling is important for reliable damage detection based on Lamb waves. A number of different numerical computational techniques have been developed for wave propagation studies. The local interaction simulation approach, used for modelling sharp interfaces and discontinuities in complex media, has been applied effectively for numerical simulations of elastic wave interaction with structural damage. The paper builds upon this experience and reports numerical investigations of Lamb wave propagation modelling for damage detection in metallic structures. The ultimate objective of the investigations is to demonstrate that numerical simulations can significantly ease the monitoring strategy used for damage detection with Lamb waves. The interaction of fundamental Lamb wave modes with a rectangular damage slot in an aluminium plate is investigated as an example. For the sake of completeness, the first part of the paper forms an introduction to wave propagation studies for damage detection. The local interaction simulation approach is implemented. This is followed by a series of two-dimensional studies of wave interaction with damage.

https://iopscience.iop.org/article/10.1088/0964-1726/16/2/003/pdf

Lamb wave propagation modelling for damage detection: I. Two-dimensional analysis

Three dimensional dynamics of pipelines buried in backfilled trenches due to oblique incidence of body waves

Three-dimensional scattering of seismic waves by a cylindrical alluvial valley embedded in a layered half-space is investigated by using the combination of the boundary integral representation and the finite element method. The surface displacements due to incident plane harmonic body waves (P, SV and SH) propagating at an arbitrary angle to the axis of the cylindrical valley are evaluated numerically for two semi-elliptical alluvial valleys. The presence of the layer is found to have a strong effect on the amplification of the surface displacements in some cases. The three-dimensional motion seems to be quite critical and may cause large amplification. The surface ground motion becomes significant when compared with corresponding free-field motion as the wavelengths become comparable to the characteristic length of the valley. The maximum amplification always occurs atop the valley. Numerical results show that the amplitude and the amplification pattern of the surface displacement strongly depend upon the frequency, the angle and the type of the incident waves.

Scattering of obliquely incident seismic waves by a cylindrical valley in a layered half-space

The evaluation of integrity of critical structures and parts is of vital importance for the maintenance of quality and safety. Quantitative nondestructive evaluation (QNDE) techniques provide the means to detect a flaw and to determine its location, size, shape and orientation. Ultrasonic technique is one of such commonly used ones. Comprehensive discussions of ultrasonic QNDE methods can be found in recent review papers by Thompson and Thompson [1] and a recent symposium volume edited by Datta et al. [2].

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=2898&context=qnde

Transient Scattering of Rayleigh-Lamb Waves by Surface-Breaking and Buried Cracks in a Plate

Three dimensional dynamics of pipelines buried in backfilled trenches due to oblique incidence of body waves : Soil Dynam Earthq Engng V10, N4, May 1991, P182–191

Dynamic response of pipelines buried in a back-filled rectangular trench in a semi-infinite medium has been investigated. The pipelines are modeled as long cylindrical shells of small thickness. By using the boundary integral representation and finite element method, we have studied the three-dimensional response to account for either pane P or SV wave incident at an arbitrary angle to the pipe-axis. In this paper numerical results are presented for the normal displacements, displacements along pipe-axis, and the hoop stresses in the pipe wall. It is shown that the response depends critically on the back-filled material as well as on the directions of propagation of the incident waves.

S. W. Liu

Papers

Three dimensional dynamics of pipelines buried in backfilled trenches due to oblique incidence of body waves

Scattering of obliquely incident seismic waves by a cylindrical valley in a layered half-space

Transient Scattering of Rayleigh-Lamb Waves by Surface-Breaking and Buried Cracks in a Plate

Three dimensional dynamics of pipelines buried in backfilled trenches due to oblique incidence of body waves : Soil Dynam Earthq Engng V10, N4, May 1991, P182–191

Dynamic Response of Pipelines Buried in Back-Filled Trenches