The intensity of the infrared radiation emitted by objects is mainly a function of their temperature. In infrared thermography, this feature is used for multiple purposes: as a health indicator in medical applications, as a sign of malfunction in mechanical and electrical maintenance or as an indicator of heat loss in buildings. This paper presents a review of infrared thermography especially focused on two applications: temperature measurement and non-destructive testing, two of the main fields where infrared thermography-based sensors are used. A general introduction to infrared thermography and the common procedures for temperature measurement and non-destructive testing are presented. Furthermore, developments in these fields and recent advances are reviewed.

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Infrared thermography for temperature measurement and non-destructive testing.

Bonded repair of composite aircraft structures: A review of scientific challenges and opportunities

In this article, the theoretical and experimental aspects of three active thermography approaches: pulsed thermography (PT), lock-in thermography (LT), and vibrothermography (VT), are discussed in relation to the nondestructive evaluation (NDE) of honeycomb sandwich structures. For this purpose, two standard specimens with simulated defects (delaminations, core unbonds, excessive adhesive, and crushed core) were tested, and results were processed, examined, and compared. As will be pointed out, the similarities and differences between these active approaches allow conclusions to be made about the most suitable approach for a particular application. In addition, results from NDE inspection by X-rays and c-scan ultrasounds are provided and discussed for reference.

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Comparative Study of Active Thermography Techniques for the Nondestructive Evaluation of Honeycomb Structures

Damage identification in aircraft composite structures: A case study using various non-destructive testing techniques

Shearography and thermography are optical techniques, both proven to be valuable tools for material nondestructive evaluation. Papers on these topics, however, are scattered and mainly appeared in optical journals. For the convenience of the materials community, this paper aims to present a comprehensive review of shearography and active thermography and their applications in nondestructive evaluation of materials. Both techniques enjoy the merits of full-field, non-contact and allowing speedy detection of material defects in metal, non-metal as well as composites materials. However, they are fundamentally different in flaw detection mechanisms. Shearography measures materials’ mechanical response to stresses, whereas active thermography measures material's heat-transfer response to an instantaneous thermal excitation. A comparison of the advantages and limitations of two techniques for nondestructive evaluation will also be presented.

/pdf/review-and-comparison-of-shearography-and-active-4i2czfwxa8.pdf

Review and comparison of shearography and active thermography for nondestructive evaluation

Aircraft composites assessment by means of transient thermal NDT

Thermal non-destructive testing (NDT) is commonly used for assessing aircraft structures. This research work evaluates the potential of pulsed thermography (PT) for certain applications. In particular, real-time monitoring was obtained using PT. In some cases, thermal modelling or other non-destructive testing and evaluation techniques (ie acoustography, ultrasonic wheel array) were also used with the intention of providing supplementary results. The following features were studied and presented: □ Through-skin sensing on aluminium (Al) alloy and carbon fibre reinforced plastic (CFRP) structures. □ Drilling-induced defects on multi-ply laminates of CFRP. □ Impact damage on CFRP fibre reinforced plastic panels and honeycomb sandwich structures. It is concluded that pulsed thermography is a rapid large-area NDT technique that can find adequate use on aircraft - aerospace materials and structures.

Pulsed thermography:philosophy, qualitative and quantitative analysis on certain aircraft applications

A comparison of acoustography, thermography and the ultrasonic wheel array for imaging impact damage in areospace composites

The necessity for more efficient and cost effective aircraft has led in the development of innovative testing and evaluation techniques. Smart and cost effective methods for evaluating the integrity of aircraft structures are necessary to both reduce manufacturing costs and out of service time of aircraft due to maintenance. Nowadays, thermal non-destructive testing and evaluation (NDT & E) techniques are frequently used in the effective assessment of composites. Such techniques are non-contact; the investigated material is heated or cooled by an external stimulus source (flash lamps, air gun, etc) and the resulting thermal transient at the surface is monitored using an infrared - thermal camera. This paper presents certain applications of thermal transient techniques relating to the investigation of composites. Different features or defects were studied: (i) notches, delaminations and fibre optics under multi-ply composite patching (bonded with FM73 adhesive film to the surface of Al 2024-T3), (ii) drilling induced defects on multi-ply laminates of HEXCEL AS4/8552 carbon fibre composites and (iii) impact damage on carbon fibre reinforced plastic (CFRP) panels and honeycomb sandwich structures (bonded with AF-163-2U.03 adhesive film). The approaches used in this study, provided first-rate results in all cases.

A. Dobbinson

Papers

Aircraft composites assessment by means of transient thermal NDT

Pulsed thermography:philosophy, qualitative and quantitative analysis on certain aircraft applications

A comparison of acoustography, thermography and the ultrasonic wheel array for imaging impact damage in areospace composites

Thermal transient thermographic NDT and E of composites