In this article, the complete characterization of the interface delamination in a composite T-joint using ultrasonic guided Lamb waves is discussed. Correlation between the numerically simulated and experimentally obtained B-scans was established. In the B-scan images, different Zones were identified and could be utilized for differentiating the healthy and delaminated T-joints. The length and the width of delamination were computed from traversing the transducers in two orthogonal directions (i.e. called the B-scans, and the D-scans). For the first time, backward propagating mode (called Turning Lamb Modes) that are generated at corner of the T-joint was observed and verfied. Using a single linear line scan of the Turning Lamb Modes, both the width and length of interface delamination could be computed. In the present study, the experiments were carried out employing air-coupled ultrasonic transducers. © 2011 Elsevier Ltd. All rights reserved.

Krishnan Balasubramaniam

Department of Mechanical Engineering

C V Krishnamurthy

Department Of Physics

Janardhan Padiyar

AIR-COUPLED ULTRASONIC TRANSDUCER

AIR-COUPLED ULTRASOUNDS

Finite element

Guided lamb waves

INTERFACE DELAMINATION

LAMB MODES

Lamb wave

Line scan

ORTHOGONAL DIRECTIONS

Propagating mode

T JOINTS

Delamination

Elastic waves

finite element method

Imaging systems

Steel sheet

transducers

Ultrasonic imaging

Ultrasonic transducers

Ultrasonic waves

Ultrasonics

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

NDT and E International

This article demonstrates a rapid, fully non-contact inspection technique for a full-scale complex composite structural component using air-coupled ultrasonic guided waves. The presence of different features such as stiffeners, stringers and geometric variations in skin-stiffened structures makes the received guided wave signal cumbersome and difficult to interpret. Experiments, supported by three-dimensional finite element models, are used to demonstrate the physics of guided wave interaction with complex features and defect configurations. B-scans are used to detect geometric variations in skin, and also disbonds in the skin-stiffener interface. Correlation between the numerically simulated and experimentally obtained B-scans is established. Different regions in the B-scan images could be used to locate and identify the defects and geometric variations in the test sample. The size of the disbond can also be computed from the B-scan. © 2018 Elsevier Ltd

Composite Structures

Rapid guided wave inspection of complex stiffened composite structural components using non-contact air-coupled ultrasound

This article reports on the characterization of delamination damages in composite laminates using wave visualization method. A combination of plate-guided ultrasound and air-coupled ultrasonics is used to locate and visualize delaminations. The study focuses on the physics of Lamb wave propagation and interaction with delaminations at various through-thickness locations and positions. Three-dimensional finite element simulations are used to study, in detail, the changes in wave features such as mode velocity, wavelength and wave refraction in the delamination region. These wave features provide information on the location, position and orientation of the delamination. These studies are validated by experimental measurements. The influence of position of source and delamination on wave refraction in the delamination region is examined. This method also correlates the results obtained from experiments and finite element simulations to theoretical dispersion curves in order to distinctly determine the delamination location. © 2016, © The Author(s) 2016.

Fulltext

Structural Health Monitoring

Characterization of delamination-type damages in composite laminates using guided wave visualization and air-coupled ultrasound

Composite materials are today widely used in engineering applications because of superior strength-weight ratios offered by them as well as high structural performance and corrosion resistance. However defects such as fibre breakage, matrix cracking, de-bonding and delaminations in composites impact their structural integrity and reliability negatively and NDE techniques to rapidly identify such defects are valuable. Ultrasonic guided waves have over the years emerged as attractive tools for scanning of large structures and recently they have been considered for rapid inspection of plate and pipe installations. Air-coupled ultrasound for generation of Lamb waves is particularly attractive for composite applications in view of the non-contact inspection offered, as well as the possibilities for rapid mechanized scanning. In this paper we present damage identification and visualisation approaches for quasi-isotropic composite plate structures, based on air-coupled plate guided ultrasonic (Lamb) waves. In the implementation demonstrated, an 8-layered quasi-isotropic [0/+45/-45/90]s glass fibre reinforced plastics (GFRP) composite plate is interrogated using air-coupled pitch-catch guided ultrasound. Propagation of Lamb waves in the laminates and their interaction with delaminations of different sizes at various locations along the structure are studied using 3D finite element (FE) analysis. The visualization approach is validated using experiments, leading to quantitative predictions of defect parameters such as sizing, location and depth. The approach is also extended for the inspection of complex composite structural features such as I- and T-sections. © 2015 AIP Publishing LLC.

AIP Conference Proceedings

An approach for defect visualization and identification in composite plate structures using air-coupled guided ultrasound

Proper alignment of air-coupled ultrasonic transducers for generation and reception of Lamb waves is vital in order to acquire a high amplitude wave group. Any misalignment with either the transmitter or the receiver or both adversely influences the amplitude of a Lamb mode. This paper reports a systematic attempt to quantify the reduction in the amplitude of the fundamental anti-symmetric Lamb mode (Ao) in a metal plate caused by misalignments in air-coupled probes. Three different types of misalignments - linear, orientation and synchronised orientation were deliberately introduced in the transducers, and experiments were performed on a 6 mm thick aluminium plate. Amplitudes of Ao mode measured at various configurations were normalised with that of Ao mode, captured in a reference configuration. Suitable curves fitted over the experimental data points revealed that Gaussian curves represent appropriately the variations in normalised amplitudes of Ao mode. Moreover, analytical expressions were derived to predict the difference in arrival times of Lamb mode(s) due to orientation and synchronised orientation misalignments. © 2014 Elsevier B.V. All rights reserved.

Effect of misalignment of air-coupled probes on Ao Lamb mode propagating in a metal plate

In this article an attempt has been made to quantitatively assess the extent of delamination in composite laminates, using time-of-flight of fundamental Lamb wave modes, without recourse to baseline data from a healthy structure. An expression has been derived to determine the delamination size, from group velocities of primary Lamb modes in the sub-laminates and time-of-flight of transmitted Ao signal and mode converted A o signal, which is generated when Ao mode propagates through a delamination. The effectiveness of the expression, when group velocities of primary Lamb modes in the main laminate were used, has been verified through numerical simulations carried out on a quasi-isotropic glass/epoxy laminate with various delamination interfaces. The effectiveness of the expression has also been verified experimentally, on two GFRP cross-ply laminates of [0/90/0] lay-up with 40 mm and 50 mm delamination sizes, using air coupled ultrasonic transducers. The predicted delamination sizes were found to be in good agreement with the actual delamination sizes. Using the proposed technique absolute identification of delamination is possible. A supplementary equation for determining the minimum length of delamination has also been derived and presented in the article. © The Author(s), 2010.

Journal of Intelligent Material Systems and Structures

Delamination size detection using time of flight of anti-symmetric (A o) and mode converted Ao mode of guided lamb waves

Propagation of the primary anti-symmetric Lamb mode (Ao) in an asymmetrically delaminated cross-ply laminate has been studied through both numerical simulations and experiments employing the air coupled ultrasonic technique. When the Ao mode interacts with the entrance and the exit of an asymmetrically located delamination, in addition to Ao, a mode converted to the primary symmetric Lamb mode (So) also propagates in each of the two sub-laminates as well as the main laminate. These Lamb modes propagate independently in each of the sub-laminates. In addition, turning modes (i.e.the mode propagating in one sub-laminate interacts with delamination edge and starts propagating in the other sub-laminate) and a mode converted turning mode (a new mode is generated during the interaction of turning mode with delamination edge) were also observed in the numerical simulation. The presence of the 'mode converted turning modes' was also validated through the experiments in this study. © 2010 IOP Publishing Ltd.

Smart Materials and Structures

Interaction of guided Lamb waves with an asymmetrically located delamination in a laminated composite plate

Structural health monitoring (SHM) of plate-like structures used in aerospace industries, using transducer arrays located suitably on the structure, such as the single-transmitter multiple-receiver (STMR) array [Wilcox PD, Lowe M, Cawley P. Lamb and SH wave transducer arrays for the inspection of large areas of thick plates. Review of progress in quantitative nondestructive evaluation, vol. 19A. Melville, NY, USA: American Institute of Physics; 1999. p. 1049-56; Wilcox PD. Guided wave beam steering from omni-directional transducer arrays. Review of progress in quantitative nondestructive evaluation, vol. 22A. Melville, New York, USA: American Institute of Physics; 2002. p. 761-8], has been demonstrated here. The reconstruction of the material state was carried out by utilizing a phased addition reconstruction algorithm. In addition to the signals from damage sites, the ultrasonic guided wave-based reconstruction procedures also need the complete set of elastic moduli as a continuous input throughout the SHM process. In the present study, two flexible printed circuit board (PCB)-based patches: ((i). single-quadrant, double-ring STMR material characterization (MC) array and (ii). Full-ring STMR SHM array) were developed for accomplishing both objectives, i.e. (a) online MC and (b) SHM of anisotropic plate-like structures, respectively. Experiments were conducted on 3.15 mm graphite-epoxy composite plate using PCB-based STMR arrays, the feasibility of accomplishing both objectives was demonstrated. © 2008 Elsevier Ltd. All rights reserved.

Structural health monitoring of anisotropic plates using ultrasonic guided wave STMR array patches

Lamb wave tomography offers a new dimension to the challenging field of in situ health monitoring of structures. The possibility of constructing tomograms from a network of sensors generating and sensing Lamb waves in thin, multi-layered, anisotropic composite plates is explored in the present study. It is shown that improved tomograms result when the anisotropic and attenuative characteristics of composite plates are accounted for by (a) using the newly identified energy of the earliest Lamb wave signals as the reconstruction parameter, (b) modifying the sensor configuration from conventional geometries (and thereby also optimizing the number of sensors), and (c) normalizing the Lamb wave energy data of the defective sample with respect to that of the defect-free sample.

Structural health monitoring of composite structures using Lamb wave tomography

Predicting delamination of composite laminates using an imaging approach

Lamb wave based ultrasonic imaging of interface delamination in a composite T-joint

Journal	NDT and E International
ISSN	09638695
Open Access	No