The international literature frequently presents optical techniques that are suitable for the comprehensive testing of valuable paintings. Nevertheless there are still some problems that are still unsolved, but infrared thermography (IR) has the potential to solve them. Unfortunately, results are not fully satisfying, mainly due to the limited reliability and the lack of a standardised procedure. Nevertheless, a review of the more recent algorithms associated with thermal non-destructive testing and evaluation shows the enormous progress of this method and the new features of modern equipment. However, even if it is a matter of direct observation in some fields, such a aerospace, this progress is not found in works of art. The main reasons are strict controls and inconsistencies typical of this application field. Analysing different reports in specialised journals, a completely new approach in one field may seem mature in another. Nowadays, mathematical modelling of the involved thermal problem supports a quantitative and precise testing and evaluation of extended fresco surfaces. The state-of-the-art indicates direct use of simulation in optimising the testing procedure. Furthermore, the solution of the direct problem allows setting up the function needed for the characterisation of defects. In this paper a totally new approach is presented, where thermal modelling allows automating the data processing, improving results. For several years, we have been studying peculiarities of detecting defects in real historical frescoes in situ, using also realistic specimens in a controlled lab environment. References and theoretical bases are given on detecting defects that are located at different depths, having different sizes. All achieved results are reported together with limiting factors, mainly due to the painted surface. Until now, in thermal non-destructive testing, all existing algorithms of data processing do not take into account 3D heat diffusion phenomena. In particular, lateral heat conduction generates false alarms and artifacts when data are processed by means of algorithms implementing a simplified 1D model. In this study, an adaptive procedure is proposed to dynamically process experimental data. By this means, artificial image sequences giving the thermal evolution of sound materials are computed, starting from initial experimental conditions. The usefulness of this approach is demonstrated, especially for the characterisation of defects buried on fresco, where surface clutter is especially significant. A fresco has been modelled with a multi-layer slab. The numerical scheme implemented has enabled us to simulate processes of dynamic heating. Experimental results are reported on plaster specimens containing a few artificial defects at different depths and tested with alternative optical NDT method. A tomography of the fresco is obtained under fast transient thermal state.
Thermal NDE enhanced by 3D numerical modelling applied to works of art
E Grinzato;S Marinetti;
2001
Abstract
The international literature frequently presents optical techniques that are suitable for the comprehensive testing of valuable paintings. Nevertheless there are still some problems that are still unsolved, but infrared thermography (IR) has the potential to solve them. Unfortunately, results are not fully satisfying, mainly due to the limited reliability and the lack of a standardised procedure. Nevertheless, a review of the more recent algorithms associated with thermal non-destructive testing and evaluation shows the enormous progress of this method and the new features of modern equipment. However, even if it is a matter of direct observation in some fields, such a aerospace, this progress is not found in works of art. The main reasons are strict controls and inconsistencies typical of this application field. Analysing different reports in specialised journals, a completely new approach in one field may seem mature in another. Nowadays, mathematical modelling of the involved thermal problem supports a quantitative and precise testing and evaluation of extended fresco surfaces. The state-of-the-art indicates direct use of simulation in optimising the testing procedure. Furthermore, the solution of the direct problem allows setting up the function needed for the characterisation of defects. In this paper a totally new approach is presented, where thermal modelling allows automating the data processing, improving results. For several years, we have been studying peculiarities of detecting defects in real historical frescoes in situ, using also realistic specimens in a controlled lab environment. References and theoretical bases are given on detecting defects that are located at different depths, having different sizes. All achieved results are reported together with limiting factors, mainly due to the painted surface. Until now, in thermal non-destructive testing, all existing algorithms of data processing do not take into account 3D heat diffusion phenomena. In particular, lateral heat conduction generates false alarms and artifacts when data are processed by means of algorithms implementing a simplified 1D model. In this study, an adaptive procedure is proposed to dynamically process experimental data. By this means, artificial image sequences giving the thermal evolution of sound materials are computed, starting from initial experimental conditions. The usefulness of this approach is demonstrated, especially for the characterisation of defects buried on fresco, where surface clutter is especially significant. A fresco has been modelled with a multi-layer slab. The numerical scheme implemented has enabled us to simulate processes of dynamic heating. Experimental results are reported on plaster specimens containing a few artificial defects at different depths and tested with alternative optical NDT method. A tomography of the fresco is obtained under fast transient thermal state.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
