Automatic detection of subsurface defects using infrared thermography: Fid-Bau Portal

Automatic detection of subsurface defects using infrared thermography

Lonkar, G.M. / Klinkhachorn, P. / Halabe, U.B. / GangaRao, H.V.S.

The popularity of FRP bridge decks has increased in recent times because of their high strength to weight ratio, fatigue resistance etc. Defects due to degradation of the bridge deck malign their properties and adversely affect the structural integrity. These defects need to be detected and continuously monitored using field techniques such as infrared thermography. The process of manually analyzing the infrared images is tedious and ambiguous. Instead, using software algorithms on the infrared images of FRP decks can increase the defect detection speed and accuracy. This paper proposes a software automated defect detection technique to detect subsurface anomalies in fiber reinforced polymer (FRP) bridge decks. Thermal images of the FRP decks were captured using a radiometric infrared camera. Software algorithms using morphological image processing and fuzzy clustering techniques were developed to analyze the images for detecting the defects automatically. They were tested on infrared images of FRP bridge decks prepared in the laboratory. In the tests conducted, simulated subsurface defects of varying size, thickness and wearing surfaces were fabricated in the laboratory. The tests include a performance analysis of detecting delaminations and debonds, and the effect of distance on the detecting ability of the algorithm. The algorithms were also tested with FRP deck specimens under solar radiation, to test the response under a passive heat source. The study showed that Infrared Thermography can be effectively used to detect subsurface defects and the process can be automated with substantial accuracy. Recent years have seen an increase in the popularity of Fiber Reinforced Polymer (FRP) composite materials due to their high strength and stiffness to weight ratio, good fatigue resistance etc. FRPs can be used to strengthen existing aging concrete structures and build new ones but defects (debonds and delaminations) in FRPs malign their properties and adversely affect the structural integrity. Debonds refer to the subsurface defects that are present at the interface between the wearing surface layer and the underlying FRP deck or between the composite wrap and underlying component. Delaminations refer to the defect present within the top or bottom flange of the deck material. These surface or subsurface defects can be visualized using Infrared Thermography (IRT). IRT is an efficient noncontact technique to detect and characterize sub-surface defects in large areas with ease. Detailed information about IRT for Non-Destructive Evaluation can be found in.