An experimental method to visualize the propagation of ultrasonic Lamb waves in composite plates with delaminations, using air coupled ultrasonic transducers, is described here. Using this method experiments are done, on glass fiber reinforced plastic(GFRP) laminates, to study the Lamb wave interactions with delamination type defects. The S0 and A0 modes are chosen for experiments at an excitation frequency of 200 kHz. Defect dimensions are calculated from the visualization images and compared with actual values. A method for detecting depth of defects using deviation of wave-fronts, at the defect contours, is presented. © 2014 AIP Publishing LLC.

Krishnan Balasubramaniam

Department of Mechanical Engineering

V. S. Sasanka Durvasula

Janardhan Padiyar M

Composite materials

Cracks

Delamination

Experiments

Imaging techniques

Nondestructive examination

Surface waves

Ultrasonic transducers

Ultrasonic waves

Visualization

Wave propagation

AIR-COUPLED

AIR-COUPLED ULTRASONIC TRANSDUCER

C-scan

Excitation frequency

Experimental methods

PWAS

ULTRASONIC LAMB WAVES

VISUALIZATION IMAGES

Ultrasonic testing

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

Visualization studies of Lamb wave propagation and interactions with anomalies in composite laminates using air-coupled ultrasonics

AIP Conference Proceedings

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.

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

Propagation of the anti-symmetric fundamental Lamb mode (A0) in a composite laminate containing a semi-infinite delamination was studied through numerical simulations and experimental studies. Here, the wave was generated on a sub-laminate above the delaminated region, and the reflection and transmission of the Lamb modes at the edge of the discontinuity were quantitatively studied. The wave group (named as 'turning mode'), which was made to propagate from one side of the delamination to the other side (through delaminations) was captured and its transmission factor was estimated. Reflection and transmission factors of wave groups were estimated for three different laminates - quasi-isotropic, unidirectional and cross-ply, containing delamination at various interfaces across thickness. Propagation of 'turning modes' were also captured experimentally, employing air-coupled transducers, in quasiisotropic laminates containing delaminations at different interfaces. Attenuation compensation was incorporated in the experimental signals to improve the comparison of transmission and reflection factors between numerical simulations and experiments. © 2011 Elsevier Ltd.

Composite Structures

Numerical and experimental studies on propagation of A0 mode in a composite plate containing semi-infinite delamination: Observation of turning modes

In the present work, the interaction of the fundamental anti-symmetric guided Lamb mode (Ao) with a structural discontinuity in a composite structure was studied through Finite Element numerical simulations and experiments. The structural component selected for this study was a T-joint section made from glass/epoxy material. This co-cured composite structure is made-up of an upper shell (skin) and a spar as the sub-components. It was observed that when Ao mode interacts with the junction (structural discontinuity) of these sub-components, a mode-converted So mode is generated. Experiments were conducted using air-coupled ultrasound to validate the numerical simulations. The back-propagating "Turning modes", which propagate from the thin region to the spar web and vice versa, were also numerically simulated and experimentally verified. © 2010 Elsevier B.V. All rights reserved.

Ultrasonics

Interaction of Lamb mode (Ao) with structural discontinuity and generation of "turning modes" in a T-joint

The quantitative assessment of both, the length and width, of a delamination in quasi-isotropic composite laminates, using experimentally generated B- and D-scan imaging techniques employing ultrasonic Lamb waves was presented. Distinct zones were identified in B- and D-scans and the sizes of zones were expressed in terms of the width and length of delamination, the probe separation distance, and the probe diameter. B-scans generated through numerical simulations gave an insight and significance of each zone. B- and D-scans were used to estimate the width and length of delaminations, respectively. The estimated width and length of delaminations were found to be in concurrence with the actual values. © 2011 Elsevier Ltd.

NDT and E International

Characterisation of rectangular type delaminations in composite laminates through B- and D-scan images generated using Lamb waves

In this study, a procedure is devised, using the fundamental symmetric Lamb mode (So) to estimate the size of an impact-induced delamination at the bottom interface of a composite laminate, which has been subjected to a low-velocity impact. When So mode incidents at the edge of delamination, it propagates independently in 0° layer and the rest of layers. Based on the propagation of So mode in the delaminated region, an expression is derived, which can estimate the size of interface delamination using measured arrival times or Time-of-Flight (ToF) of So modes. Numerical simulations were carried out on glass/epoxy (GFRP) cross-ply laminates ([0/902]s) to confirm the derived expression and eventually it was validated through experiments carried out on [0/90/0] GFRP laminates. Moreover, the minimum detectable size of delamination through the proposed method was estimated analytically and verified through numerical simulations. © The Author(s) 2011.

Fulltext

Journal of Reinforced Plastics and Composites

Sizing of delamination using time-of-flight of the fundamental symmetric Lamb modes

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

Journal	Data powered by TypesetAIP Conference Proceedings
Publisher	Data powered by TypesetAmerican Institute of Physics Inc.
ISSN	0094243X
Open Access	No