Detection of dis-bond between honeycomb and composite facesheet of an Inner Fixed Structure bond panel of a jet engine nacelle using infrared thermographic techniques

ABSTRACT

The Inner Fixed Structure (IFS) bond panel is a honeycomb sandwich panel with CFRP facesheet and a heat shield on one side, and a perforated CFRP facesheet on the other side, of a jet engine nacelle. It is subjected to extreme temperature on both sides which damages the inner epoxy adhesive bond between the facesheet and the honeycomb core. Accessibility to this layer for non-destructive evaluation is extremely challenging using conventional methods. This work proposes active thermography techniques such as flash thermography and induction thermography for accessing the inner layer. The infrared camera utilises the perforations in the facesheet of the IFS bond panel, which is used for attenuating the engine noise, for imaging the defects. However, flash thermography requires the removal of the thermal insulation layer for the inspection, whereas induction thermography can be performed without any modifications to the structure. The minimum detectable dis-bond size using these techniques is restricted to the spacing between the perforations on the facesheet. A numerical model has developed for induction thermography to optimise the excitation frequency that can produce reasonable thermal contrast at the inner facesheet and minimum temperature rise on the intermediate stainless-steel thin sheet that covers the thermal insulation layer.

KEYWORDS:

• IFS bond panel
• dis-bond
• honeycomb
• nacelle
• composite
• flash thermography
• induction thermography

Acknowledgments

The samples were provided by UTC Aerospace Systems, Chula Vista, CA, USA, and the work effort was partially supported under the contract PO 2571134 issued by Goodrich Aerostructures, Singapore. The authors thank the program managers Mr. Jared Victor and Mr. Vijay Pujar, for technical inputs during the research work.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Correction Statement

This article has been republished with minor changes. These changes do not impact the academic content of the article.

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Notes on contributors

Renil Thomas Kidangan

Renil Thomas Kidangan received his undergraduate degree in Mechanical Engineering from Calicut University, Kerala, India in 2012. He is currently pursuing his M.S. and Ph.D. in NDT at the Center for Non-Destructive Evaluation (CNDE),  in the Department of Mechanical Engineering, Indian Institute of Technology Madras, India. His area of specialization is the inspection of composites using infrared thermography. His research interests include finite element based multi-physics modeling, image processing, and their applications in the field of thermal NDT.

Chitti Venkata Krishnamurthy

Krishnamurhty Venkata is currently an Associate Professor in the Department of Physics at Indian Institute of Technology Madras (IIT Madras), India. He obtained his Ph.D. from IIT Madras in 1989. He has over 125 technical publications and has presented papers at several national and international conferences. His research interests are thermal NDT, modeling, and simulation of electromagnetic wave, acoustic, elastic wave propagation and scattering, nonlinear ultrasonic wave propagation in liquids and solids, heat diffusion in anisotropic media.

Krishnan Balasubramaniam

Krishnan Balasubramaniam is currently Institute Professor of Indian Institute of Technology Madras (IIT Madras), Chair Professor in the Department of Mechanical Engineering, and also serves as the Head of the Center for Non-Destructive Evaluation (CNDE) at IIT Madras. He graduated from Drexel University with an M.S. degree in 1986 and a Ph.D. in the year 1989. Before joining IIT Madras in 2000, he was employed as Tenured Associate Professor at Mississippi State University. He has been involved in the field of NDT for more than 33 years with applications in the fields of maintenance, quality assurance, manufacturing, and design. His area of research interests includes in-process monitoring, structural health monitoring, micro and nano-imaging, material characterization, wave propagation. He has numerous patents and publications in the area of non-destructive testing.