Detection of structure anomalies in frescos: A comparison between thermography and laser Doppler vibrometry techniques

Abstract

This work will investigate two non-destructive methods of fault detection in laminate structures such as frescos. These two techniques are compared on a purpose-built laboratory prototype and on frescos in the Senate Reception Room of the U.S. Capitol Building. Thermography uses an infrared camera to map the surface temperature of an object. This technique can be used to quickly identify abnormally hot or cold regions on a surface. These abnormal regions can indicate structural defects such as fresco delamination, cracks, and inclusions. The other non-destructive technique for defect detection used in this work is laser Doppler vibrometry paired with acoustic excitation of the target surface. Over the same surface area, thermography provides a much quicker result. This work aims to evaluate potential synergy between the technologies by comparing the results of the two scans. A prototype with known defects is used to find commonality between the two methods and to understand the circumstances in which the results diverge. The prototype is a square of approximately half a meter on each side. A seven centimeter thick concrete backing layer is followed by a layer of mortared antique bricks and topped by mortar and plaster to mimic fresco.This work will investigate two non-destructive methods of fault detection in laminate structures such as frescos. These two techniques are compared on a purpose-built laboratory prototype and on frescos in the Senate Reception Room of the U.S. Capitol Building. Thermography uses an infrared camera to map the surface temperature of an object. This technique can be used to quickly identify abnormally hot or cold regions on a surface. These abnormal regions can indicate structural defects such as fresco delamination, cracks, and inclusions. The other non-destructive technique for defect detection used in this work is laser Doppler vibrometry paired with acoustic excitation of the target surface. Over the same surface area, thermography provides a much quicker result. This work aims to evaluate potential synergy between the technologies by comparing the results of the two scans. A prototype with known defects is used to find commonality between the two methods and to understand the circumstances in which the ...