Quality assurance of the composite products becomes important to avoid defects during processing since they are used for critical applications. Non- Contact Ultrasound (NCU) technique using the A0 Lamb modes is explored here with applications in the detection, imaging, and sizing of defects in both honeycomb and more importantly composite laminates. A Finite Element Model was employed to understand the interactions of the Lamb modes with defects. Mode conversions at the two ends of a delamination and the time of flight differences between these were employed for the determination of the size of the delaminations in composite laminates. This method may allow for the two dimensional sizing of the delaminations in composite laminates using a single line-scan using the Lamb modes. © 2009 American Institute of Physics.

Krishnan Balasubramaniam

Department of Mechanical Engineering

P. Karthikeyan

C. Ramdas

Mahesh C. Bhardwa

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

Non‐contact ultrasound based guided lamb waves for composite structure inspection: some interesting observations

AIP Conference Proceedings

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 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.

Fulltext

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.

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