Application of non-invasive active infrared thermography for delamination detection in fresco

In the most common method of fresco painting, a unique integration of paint and plaster allows for frescos to acquire great durability and permanence. As the plaster or layers of fresco walls deteriorate over time, frescos become vulnerable to serious damage. In order to prevent such damage without harming frescos, non-destructive techniques must be used to analyze and determine areas of structure delamination. In the past, different non-destructive methods have been studied. However, many require expensive equipment. The main scope of this work is the evaluation of the effectiveness of non-invasive detection of fresco delamination via thermography, a comparatively inexpensive technique. In non-invasive active infrared thermography, thermal images are captured of a fresco before, during, and after a heating or cooling process. A defect beneath the surface acts as an insulative pocket, which in turn entraps heat and decreases the rate of heat diffusion. The accumulation of heat results in a defective region being abnormally hotter than a non-defective region, which causes a greater change in temperature throughout a heating or cooling process. Therefore, the analysis of the temperature change highlights defects location and entity beneath the surface. This technique was used and validated with two constructed surrogates, one with a known defect and one without a defect. The thermal analysis of the surrogates was performed via MATLAB®. Additionally, simulations of heating and cooling processes on modeled surrogates were generated in COMSOL® Multiphysics. The results of these simulations assessed the MATLAB® analysis and the use of non-invasive thermography as a tool to detect fresco delaminations. This method was then implemented on frescos within the Senate Reception Room of the United States Capitol Building.