Assessment of crack bridging in coating systems : a comparative study between Digital Image Correlation (DIC) and dial gauges in crack bridging tests

Abstract

This study evaluated the crack-bridging capacity of textured coating systems across 60 test specimens using an adapted UEAtc test method, comparing analog dial gauges with twodimensional Digital Image Correlation (2D-DIC) on acrylic and mortar substrates. Acrylic substrates achieved higher mean bridged crack widths (0.97 to 1.20 mm via dial gauges and 0.39 to 0.51 mm via DIC) than mortar prisms (0.30 to 0.42 mm via dial gauges and 0.21 to 0.36 mm via DIC). The elastomeric topcoat increased nominal crack-bridging by up to 46.2% in DIC measurements, although substrate type was the mechanically dominant factor in the ANOVA (p < 0.001). Bland–Altman analysis indicated a systematic mean bias of −0.38 mm and significant proportional bias (y = −1.18x + 0.28; R 2 = 0.61), demonstrating close agreement for narrow cracks (<0.40 mm) and progressive divergence at larger openings due to mechanical contact seating effects (ICC(2, 1) = 0.21). The main limitations stem from the spatial disparity between discrete substrate fixtures and continuous surface tracking. In conclusion, DIC is a reliable, non-contact technique for mapping continuous strain fields and identifying initial microcracking, but it cannot directly replace mechanical contact gauges across large deformation ranges without bias compensation.