Xavier Maldague

Procesamiento de imágenes infrarrojas para la detección de defectos en materiales

El Ensayo Termografico No Destructivo (ETND) es una tecnica de evaluacion de materiales, en la que la superficie de una muestra de material es estimulada tecnicamente para producir una diferencia de temperatura entre las areas no defectuosas y las eventualmente defectuosas. Los cambios de temperatura son registrados mediante una camara infrarroja; posteriormente, dada la distorsion generada por el ruido, se ejecutan etapas de procesamiento para detectar y/o caracterizar los defectos en el material. En este articulo se analizan y comparan experimentalmente varios de estos metodos de procesamiento y se profundiza en la tecnica CAD (Contraste Absoluto Diferencial) modificada por cuadrupolos termicos.

Thermal transient thermographic NDT and E of 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.

The role of the continuous wavelet transform in mineral identification using hyperspectral imaging in the long-wave infrared by using SVM classifier

Hyperspectral imaging (HSI) in the long-wave infrared spectrum (LWIR) provides spectral and spatial information concerning the emissivity of the surface of materials, which can be used for mineral identification. For this, an endmember, which is the purest form of a mineral, is used as reference. All pure minerals have specific spectral profiles in the electromagnetic wavelength, which can be thought of as the mineral’s fingerprint. The main goal of this paper is the identification of minerals by LWIR hyperspectral imaging using a machine learning scheme. The information of hyperspectral imaging has been recorded from the energy emitted from the mineral’s surface. Solar energy is the source of energy in remote sensing, while a heating element is the energy source employed in laboratory experiments. Our work contains three main steps where the first step involves obtaining the spectral signatures of pure (single) minerals with a hyperspectral camera, in the long-wave infrared (7.7 to 11.8 μm), which measures the emitted radiance from the minerals’ surface. The second step concerns feature extraction by applying the continuous wavelet transform (CWT) and finally we use support vector machine classifier with radial basis functions (SVM-RBF) for classification/identification of minerals. The overall accuracy of classification in our work is 90.23± 2.66%. In conclusion, based on CWT’s ability to capture the information of signals can be used as a good marker for classification and identification the minerals substance.

A novel optical air-coupled ultrasound NDE sensing technique compared with infrared thermographic NDT on impacted composite materials

In this paper, a novel optical air-coupled ultrasound (O-ACU) technique is proposed. A wide broadband (100 KHz - 1 MHz) laser-acoustic based optical microphone worked as probe in an air-coupled ultrasound (ACU) system. The O-ACU modality was used to detect several CFRP and GFRP impacted laminates and the results were compared with the classical ACU modality. Infrared thermography, as an established reference technique, was used for the validation. Advanced image processing techniques were applied. Conclusively, O-ACU shows an obvious improvement in sensibility and resolution.

a new thermal contrast for non-destructive thermographic testing of materials

It is known that methods of thermographic non destructive testing (TNDT) based on thermal contrast are strongly affected by non-uniform heating at the surface. Hence, the results obtained from these methods considerably depend on the chosen reference point. The differential absolute contrast (DAC) method was developed to eliminate the need of determining a reference point that defines the thermal contrast with respect to an ideal (sound) area. Although DAC is very useful at early times, the DAC accuracy decreases at later times when the heat front approaches the sample rear face. In this article, a new DAC version is proposed by explicitly introducing the sample thickness and using the thermal quadrupoles theory. It is shown that the validity of the new DAC version increases for long times while being preserved at short times.