In this work, pulsed phase thermography (PPT), principal component thermography (PCT), and partial least squares thermography (PLST) techniques were applied in order to detect the masonry texture, as well as to map the subsurface damages formed beneath three different mural paintings. The latter were inspected after the 2009 earthquake, <i>i.e.</i>, the seismic event that devastated L’Aquila City (Italy) and its surroundings. The mural supports explored by infrared thermography (IRT) are constituted by a single leaf, and the sides of the inspected paintings are confined by marble frames or by buried horizontal and vertical structures. Hence, the analyzed objects can be considered as monolithic structures. IRT can help to understand the masonry morphology, e.g. if there exist structural continuity between the <i>arriccio </i>layer (the first coat of plaster) and the support. In the present case, the heating phase was provided by lamps or propane gas and feature detection was enhanced by advanced signal processing. A comparison among the results is presented. Two of the three objects analyzed, painted by the art masters <i>Serbucci </i>and <i>Avicola</i>, are preserved inside <i>Santa Maria della Croce di Roio </i>Church in Roio Poggio (L’Aquila, Italy); they were executed on two masonries built in different periods. The last one was realized in <i>Montorio al Vomano</i> (Teramo, Italy) on the internal cloister of the <i>Zoccolanti’s Church </i>(undated). The villages are separated by 50 km as the crow flies. Finally, near-infrared reflectography (NIRR) technique was also used to investigate the condition of the painting layer.
This work focuses in the implementation of infrared and optical imaging techniques for the inspection of aeronautics parts. To this aim, a helicopter blade with known defects is inspected with four different techniques: long pulse thermography, pulsed thermography, digital speckle photography (DSP) and holographic interferometry (HI). The first two techniques belongs to the group of infrared imaging techniques, which are based on the analysis of the infrared thermal patterns in order to detect internal anomalies in the material; whilst the last two (DSP and HI) corresponds to the optical imaging techniques which make use of visible light to measure the material response to an applied stress. Both techniques were applied using the active approach, i.e. an external stimulation is applied in order to produce a gradient in either, the thermal and/or displacement field of the material. The results are then compared in order to evaluate the advantages and limitations of each technique.
Infrared thermography is a valuable tool for non-destructive evaluation of antique artworks. Active thermographic
techniques can be applied on-site thanks to their contactless and non-invasive nature. On-site monitoring is a challenging
task. The observed objects are often hard to reach and of unknown thermal and physical properties. Moreover there are
usually hard constraints on the availability of the site, in terms of space and time. For these reasons the acquired data are
typically inhomogeneous and need to be reorganized and post-processed, with dedicated algorithms, to enhance the
The frescoes of the San Gottardo Church, located in Asolo, in the North-East of Italy, are showing multiple detachments
due to the ageing process. More than 60 frescoed surfaces have been selected for evaluation via an active thermography
procedure. Each area has been heated with handheld air heaters and a sequence of infrared images of the cooling process
has been recorded.
Several techniques are available for the post-processing of thermographic sequences. In this work standard algorithms,
such as correlated contrast and principal component thermography, are compared with new ones. We propose two new
algorithms, the first is based on sum and filtering, the second is an adaptation of the partial least squares method to
thermography. The obtained results allow to identify and locate the most important detachments on the surfaces.
Pulsed Thermography (PT) is one of the most widely used approaches for the inspection of composites materials, being its main attraction the deployment in transient regime. However, due to the physical phenomena involved during the inspection, the signals acquired by the infrared camera are nearly always affected by external reflections and local emissivity variations. Furthermore, non-uniform heating at the surface and thermal losses at the edges of the material also represent constraints in the detection capability. For this reason, the thermographics signals should be processed in order to improve – qualitatively and quantitatively – the quality of the thermal images. Signal processing constitutes an important step in the chain of thermal image analysis, especially when defects characterization is required. Several of the signals processing techniques employed nowadays are based on the one-dimensional solution of Fourier’s law of heat conduction. This investigation brings into discussion the three-most used techniques based on the 1D Fourier’s law: Thermographic Signal Reconstruction (TSR), Differential Absolute Contrast (DAC) and Pulsed Phase Thermography (PPT), applied on carbon fiber laminated composites. It is of special interest to determine the detection capabilities of each technique, allowing in this way more reliable results when performing an inspection by PT.