Estimating Thermal Material Properties Using Solar Loading Lock-in Thermography

Featured Application Thermographic monitoring of a retaining wall structure. This work investigates the application of lock-in thermography approach for solar loading thermography applications. In conventional lock-in thermography, a specimen is subjected to a periodically changing heat flux. This heat flux usually enters the specimen in one of three ways: by a point source, a line source or an extended source (area source). Calculations based on area sources are particularly well suited to adapt to solar loading thermography, because most natural heat sources and heat sinks can be approximated to be homogenously extended over a certain region of interest. This is of particular interest because natural heat phenomena cover a large area, which makes this method suitable for measuring large-scale samples. This work investigates how the extended source approximation formulas for determining thermally thick and thermally thin material properties can be used in a naturally excited setup, shows possible error sources, and gives quantitative results for estimating thermal effusivity of a retaining wall structure. It shows that this method can be used on large-scale structures that are subject to natural outside heating phenomena.

Automated summary

This study investigates the application of lock-in thermography for solar loading thermography, highlighting the suitability of calculations based on area sources for large-scale structures. It provides an overview of extended source approximation formulas for determining material properties and demonstrates the practical application in estimating thermal effusivity of a retaining wall structure subject to natural outside heating phenomena.