P. Venegas

Infrared thermography for temperature measurement and non-destructive testing.

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.

Mobile speckle interferometer in the long-wave infrared for aeronautical nondestructive testing in field conditions

Abstract. We present the development of a speckle interferometer based on a CO2 laser and using a thermal infrared camera based on an uncooled microbolometer array. It is intended to be used for monitoring deformations as well as detecting flaws in aeronautical composites, with a smaller sensitivity to displacement compared to an equivalent system using visible (VIS) lasers. Moreover the long wavelength allows working with such interferometers outside the laboratory. A mobile system has been developed on the basis of previous laboratory developments. Then it is validated in a variety of industrial nondestructive testing applications in field working conditions.

Fiber Bragg Gratings, IT Techniques and Strain Gauge Validation for Strain Calculation on Aged Metal Specimens

This paper studies the feasibility of calculating strains in aged F114 steel specimens with Fiber Bragg Grating (FBG) sensors and infrared thermography (IT) techniques. Two specimens have been conditioned under extreme temperature and relative humidity conditions making comparative tests of stress before and after aging using different adhesives. Moreover, a comparison has been made with IT techniques and conventional methods for calculating stresses in F114 steel. Implementation of Structural Health Monitoring techniques on real aircraft during their life cycle requires a study of the behaviour of FBG sensors and their wiring under real conditions, before using them for a long time. To simulate aging, specimens were stored in a climate chamber at 70 °C and 90% RH for 60 days. This study is framed within the Structural Health Monitoring (SHM) and Non Destructuve Evaluation (NDE) research lines, integrated into the avionics area maintained by the Aeronautical Technologies Centre (CTA) and the University of the Basque Country (UPV/EHU).

Development of Virtual Illumination Functions for Thermographic NDT

This study develops and analyses a novel mathematical approach for thermographic NDT data processing. This approach is based on the definition of a simplified 2D thermal diffusion model to which usual processing algorithms are applied to produce analysis functions, which considers information related to temperature values, material properties and heating conditions. The analysis of the developed functions has been conducted with thermal data computationally generated in order to provide broad variety of case studies regarding different types of defects as well as stimulations. The results obtained have demonstrated that these functions may provide information useful in defect characterisation.

Simultaneous Temperature and Deformations Measurements Using Long-Wave Infrared Speckle Interferometry: A Novel Hybrid Technique for Industrial Nondestructive Testing

Since its demonstration in 2003 [1], the use of long-wave infrared (LWIR) CO2 lasers in Digital Holography (DH) has been shown in an increasing number of applications. In particular it allows observing large objects and in metrology it allows measuring large displacements while rendering holography more immune to environmental perturbations, compared to holography in the visible. For metrology we demonstrated various holographic techniques in LWIR: speckle interferometry [2,4], DH interferometry [2-4] and shearography [4]. The LWIR holographic set-up generally makes use of microbolometer arrays based thermal imagers. The present paper discusses some result of the European project FANTOM in which another advantage was put forward when speckle interferometry is applied in LWIR: the thermal background is captured simultaneously to the specklegrams since it constitutes an offset in the signal. Therefore one can correlate uniquely the temperature and displacement information at the same time and in each pixel. We describe here the successful achievements of the project.