Damage Detection on Frescoes Paintings by Active IR-Thermography Soft-Sensing

摘要

Active thermography is a Non Destructive Technique (NDT) for composite materials testing, largely applied in aeronautics applications. Some previous works have also demonstrated its power for damage detection in frescoes and paintings. Active thermography is based on the measurement of the 2D thermal emission of an object surface when the object is exposed to a thermal flux. The thermal flux propagation inside the object affects its surface temperature and emissivity, which can be measured by an Infra-Red (IR) thermal camera. The presence of defects inside the object, as detachment between different layers, modify the propagation of the heat flow and consequently the surface temperature distribution, which can be used for the damage identification. Unfortunately, damage detection is often based on the subjective identification of discontinuities in the thermal maps that typically relies on the operator expertise. To make the identification objective, simplified mono-dimensional models have been used for the detachment modelling and for grounding their recognition and localization on a correlation between experimental thermograms and modelled ones. This paper proposes a new approach linking the experimental 2D measurements to a FE model of the element under test in order to update the model with the measured data and optimise its inputs, i.e. the thermo-mechanical characteristics of the object, to be able to localise a potential damage and its depth. In this work, the authors have performed a feasibility analysis of the method, have optimised the computational effort and have experimentally determined the properties of the material, which the object under test is made of, that have a strong influence on the uncertainty of the method itself. The 3D extension of the model is under evaluation and it will be included in a future work.