3 April 2015 Heat transfer computed tomography techniques for damage detection in metallic structures
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The detection of damage in structures at its earliest stages has many economical and safety benefits. Permanent monitoring systems using various forms of sensor networks and analysis methods are often employed to increase the frequency and diagnostic capabilities of inspections. Some of these techniques provide spatial/volumetric information about a given area/volume of a structure. Many of the available spatial sensing techniques can be costly and cannot be permanently deployed (e.g., IR camera thermography). For this reason intricate analysis methods using permanently deployable sensors are being developed (e.g., ultrasonic piezoelectrics, sensing skins). One approach is to leverage the low cost of heaters and temperature sensors to develop an economical, permanently installable method of spatial damage detection using heat transfer. This paper presents a method similar to that of X-ray computed tomography (CT). However, the theories for Xray CT must be adapted to properly represent heat transfer as well as account for the relatively large and immobile sensors spacing used on a structure (i.e., there is a finite number of heaters/sensors permanently installed around the perimeter of the area of interest). The derivation of heat transfer computed tomography is discussed in this paper including two methods for steering the effective heat wave. A high fidelity finite element method (FEM) model is used to verify the analytical derivation of individual steps within the method as well as simulate the complete damage detection technique. Experimental results from both damaged and undamaged aluminum plate specimens are used to validate the FEM model and to justify theoretical assumptions. The simulation results are discussed along with possible improvements and modifications to the technique.
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Nephi R. Johnson, Nephi R. Johnson, Jerome P. Lynch, Jerome P. Lynch, Ann E. Jeffers, Ann E. Jeffers, "Heat transfer computed tomography techniques for damage detection in metallic structures", Proc. SPIE 9435, Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2015, 943529 (3 April 2015); doi: 10.1117/12.2086845; https://doi.org/10.1117/12.2086845

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