Reference-free infrared thermography detection with subsurface heating for deep cavity in adhesive of hidden frame glass curtain wall

Abstract

Since the current infrared thermography (IRT) is not effective in detecting deep and invisible cavities in the silicone structural adhesive of hidden frame glass curtain walls (HFGCW), a reference-free IRT with subsurface heating for the deep cavity is proposed. A near-infrared linear laser with high energy density and high transmission is chosen as the subsurface heating source to directly heat the silicone structural adhesive through the glass. Temporal sequence reconstruction and image enhancement based on reference-free calibration are proposed to reduce thermal inhomogenety and thermal noise and ensure comparable results for damage detection under different environments. The effects of traditional surface heating and subsurface heating are compared and analyzed through numerical simulations. And an evaluated feature, which is the maximal temperature difference feature, derived from temperature difference is used to quantitatively analyze the thermal effect caused by different cavities. The subsurface heating simulation results showed that the highest temperature difference between the region with cavity and defect-free region is up to 88% higher than that of traditional surface heating. The experiments revealed that the deep cavities of different lengths, located at 7 mm, 9 mm, and 11 mm below the glass surface, can be successfully detected using subsurface heating and reference-free calibration. A quadratic linear model is proposed to reflect the relationship between the depths and lengths of cavities and the evaluated feature. In conclusion, the proposed method can protect the HFGCW from deep and invisible cavities which can reduce its adhesion and strength.