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Localized and distributed guided ultrasonic waves array systems offer an efficient way for the structural health monitoring of large structures. The detection sensitivity for fatigue cracks depends on the orientation of the crack relative to the location of the sensor elements. Crack-like defects have a directionality pattern of the scattered field depending on the angle of the incident wave relative to the defect orientation and on the ratio of the defect depth and length to the wavelength. From FE simulations it has been shown that for cracks and notches almost no energy is scattered in certain directions from the defect, i.e., the data processing algorithm must take into account that for some transducer combinations no change in the signal even for a significant defect will be detected. The scattered wave field directionality pattern for an incident low frequency A0 Lamb wave mode was predicted from 3D Finite Element simulations and verified from experimental measurements at machined part-through and through-thickness notches using a laser interferometer. Good agreement was found and the directionality pattern can be predicted accurately. The amplitude of the scattered wave was quantified for a systematic variation of the angle of the incident wave relative to the defect orientation, the defect depth, and the ratio of the characteristic defect size to the wavelength. Based on these results the detection sensitivity for crack-like defects in plate structures using guided wave sensor arrays can be quantified. [ABSTRACT FROM AUTHOR]

This paper addresses a gap in the literature on the 3-dimensional scattering of the fundamental symmetric Lamb mode S0 from delimitations in composite plates. We study the scattering of low-frequency S0 Lamb mode from a delamination in a stiffened 4-ply CFRP composite plate with [0/0]S ply orientation. Far field scattering coefficients for the S0 Lamb mode are plotted as a function of circumferential position around the delamination using 3D FE simulations. Results show that the delamination size has less influence on S0 Lamb wave scattering in the low-frequency regime where the S0 mode is non-dispersive. Further analysis was done using two-dimensional FE simulation for different ply-layup orientations with S0 Lamb mode. This study shows that ply-layup orientation and through-thickness delamination location in fiber composite laminate have a significant influence on S0 Lamb mode interaction. We also analyzed the interaction of A0 Lamb mode for a few cases. This work will be useful for practical Lamb wave based inspection of composite plate structures. [ABSTRACT FROM AUTHOR]

The non-destructive testing of materials can be conducted by various techniques. Amongst these, method based on ultrasonic waves is one of the most common one. Of these ultrasonic waves Lamb waves are of particular interest for the inspection of large structures for various reasons. Scattering of Lamb waves from flaws has generated a considerable amount of research over last couple of decades. Most of the work has been done using computational tools like Finite Element Methods and experimental technique. In this paper an analytical approach is presented to develop a fundamental understanding of the scattering of Lamb waves from geometric discontinuities in 2 dimensions. We have considered simplest of all geometric discontinuity - a step, as this fundamental understanding can easily be extended to corrosion or crack. [ABSTRACT FROM AUTHOR]

Guided waves (GW) are used to inspect pipeworks in various industries. Specific features of pipeworks lead to complex scattering phenomena. Simulations tools able to handle such a complexity must be developed to help interpretation and to optimize testing configurations. They must handle both long range propagation and local scattering phenomena. Here, a modal formulation is derived to deal with pipeworks comprising arbitrarily curved elbows linking otherwise straight pipes. First, the semi-analytic finite element method is extended in curvilinear coordinates to predict guided modes in elbows. Then, GW scattering at the junction of a straight pipe with an elbow is investigated. Modal solutions in both parts being known, the mode matching method is derived to compute modal reflection and transmission coefficients given as elements of a scattering matrix. Further, the global scattering matrix of a pipework comprising an arbitrary number of elbows linking straight pipes is considered. A general formulation presented in this conference series is used which handles multiple scattering phenomena that possibly arise. Interestingly, the computation of both modal solution and the scattering matrix with mode-matching method only requires meshing the pipe section. Examples illustrate the various steps. [ABSTRACT FROM AUTHOR]

One critical factor affecting the performance of Lamb wave based damage detection and characterization techniques is the angular amplitude distribution of the interrogating wave scattered at defects and structural features. Analytical solutions for this problem do not exist for composite laminates due to the anisotropic nature and multilayer characteristics of the material. In this paper the scattering characteristics of the fundamental anti-symmetric Lamb wave at delaminations and structural features in composite laminates is considered. Experimental measurements and finite element simulations are employed to quantify the A0 mode Lamb wave scattering characteristics at delaminations and through holes. Good agreement is found between the simulations and experimental measurements. Extended parameter studies provide improved physical insight into the phenomena and show that the angular distributions of the scattered wave amplitudes depend on the defect size to wavelength ratio, the stacking sequence of the laminate and, in the case of delamination damage, the through thickness location of the delamination. [ABSTRACT FROM AUTHOR]

The scattering of guided waves by a complex shaped defect in a three-dimensional (3D) waveguide is considered. For such problems, analytical solutions do not exist, and modal decomposition techniques based on the establishment of the displacement and stress fields in the vicinity of the scatterer are extremely heavy and complicated. On the other hand, finite elements (FE) based methods are known to be very memory consuming. This paper proposes a post-processing technique, based on a 3D orthogonality relation, to decompose a complex acoustic field produced by a scatterer and predicted by a 3D finite elements model, into plane waves, the amplitudes of which are quantified. This technique allows huge reductions of the (FE) model size to be obtained. An application of guided waves scattering in an aluminium plate is presented, where zero and first order Lamb and SH modes compose the scattered field. [ABSTRACT FROM AUTHOR]