LASer & Electro optical Research in engineering metrology
The LAS.E.R. Laboratory, specialized in Optical Engineering, was founded in 1972. Its major research topics include holographic interferometry, NDT by speckle methods and IR thermography, flow visualization and artwork diagnostics. Professor Domenica Paoletti is emeritus head of the LAS.E.R. Laboratory.
RESEARCH LINES AND PROJECTS
A diagnostic centre, modelled along the lines suggested by the fundamental research in coherent optics, has been developed at the University of L'Aquila since 1970s years. The aim was to define non destructive optical methodologies in the diagnostics of artworks (paintings, frescoes, mosaics, statues, etc.).
The laboratory deals with the application of NDT (mainly thermography) on buildings (also historical) to reveal defects and hidden structures.
Optical methods are well known tools in flow visualization. The laboratory contributed new techniques and applications in diffusivity measurements in liquids as well as measurements in heat transfer studies.
Speckle Techniques are a growing field since their introduction in the 1970s years. The laboratory dealt with ESPI and other speckle-based methods.
Infrared thermography involves passive and active procedures.
In the first case, the test object releases heat. Observing and analyzing the cooling process, it is possible to reveal defective areas which are detectable due to the presence of thermal anomalies.
In active thermography, the test object is heated up by an external source.
The presence of a significant temperature difference pinpoints subsurface anomalies. In general, active thermography includes Pulsed Thermography (PT), Pulsed Phased Thermography (PPT), Thermal Contrast (TC), Step Heating Thermography (SH), Lock-in Thermography (LT) and Vibrothermography (VT).
These techniques are briefly described in the following.
In Pulsed Thermography the test sample is heated up for a short period of time. This heating produces a thermal pulse that propagates into the sample by thermal diffusion. During the pulse propagation, an infrared camera is used to record temperature distribution on the sample surface. A subsurface defect, if present, modifies the diffusion heat flow so its location appears as an area with a temperature difference with respect to the surrounding area.
Pulsed Phased Thermography is a practical way to analyze data obtained from a PT experiment. A short pulse of energy is applied to the surface of the specimen to be analyzed using lamps or powerful photographic flashes.
In Step Heating Thermography, the sample is constantly heated starting at a certain point of time. During the heating, the temperature evolution is observed.
In Lock-in Thermography the sample is heated up periodically, generating thermal waves inside. For instance, a sine-modulated heating can be used.
Vibrothermography is based on an effect of direct conversion from mechanical to thermal energy. The inspected sample is subjected to mechanical excitation that causes a friction effect in places where the defects (delamination, cracks, etc.) are located. Due to friction, a certain amount of energy is released, pinpointing the defect location.
Integrated NDT techniques
Sometimes the use of integrated NDT techniques is recommended because the detection of defects may be linked to the wavelengths (or frequencies) used during the inspection, as well as to the nature of the defect itself. In this section, some works performed by the Las.E.R. Laboratory are shown. Different techniques cooperated together