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.

Krishnan Balasubramaniam

Department of Mechanical Engineering

Janardhan Padiyar

Arrival time

composite laminate

Cross-ply laminate

GFRP LAMINATES

Glass/epoxy

Impact

IMPACT-INDUCED DELAMINATION

INTERFACE DELAMINATION

LAMB MODES

Lamb wave

Low velocity impact

TIME OF FLIGHT

Computer simulation

finite element method

Flight simulators

Laminates

Numerical methods

Steel sheet

Delamination

Fulltext

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

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

Journal of Reinforced Plastics and Composites

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.

AIP Conference Proceedings

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

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

The interaction of an ultrasonic guided Lamb wave mode with delamination type defects in a quasi-isotropic laminated composite plate has been studied, using both simulations and experiments. In a laminated composite plate with a symmetric delamination, when the primary anti-symmetric mode, Ao, is incident at the entrance and exit of a delamination, it generates a new mode, So, that is confined only to sub-laminates and undergoes multiple reflections in the delaminated region. It was observed that only the incident and mode-converted Ao modes propagate in the main laminate. The two modes reverberate between the two ends of the delaminations while undergoing multiple mode conversions, leading to a trail of signals that is captured by the finite element model. The numerical observations were validated using experiments conducted using air coupled ultrasonic transducers. © 2009 IOP Publishing Ltd.

Interaction of the primary anti-symmetric Lamb mode (Ao) with symmetric delaminations: Numerical and experimental studies

The Finite Element Method in Engineering

Finite Element Analysis Using ANSYS ∗ ∗ANSYS FEM software is marketed by ANSYS, Inc., Southpointe, 275 Technology Drive, Canonsburg, PA 15317.

Composite Structures

Interaction of Lamb waves on bonded composite plates with defects

Journal	Journal of Reinforced Plastics and Composites
ISSN	07316844
Open Access	No