Automatic Optical Crack Tracking for Double Cantilever Beam Specimens

An automatic crack tracking scheme is developed for measuring the tensile opening (mode I) interlaminar fracture toughness (G_Ic) of continuous glass fiber-reinforced composite materials. The technique is directly compared to ASTM standard D5528, which contains a manual procedure to obtain G_Ic values from crack length data using a double cantilever beam (DCB) specimen. In this study, a custom computer program with edge detection software rapidly, automatically, and accurately tracks the crack front in translucent DCB specimens by optically monitoring dissimilarities between delaminated and intact portions of the sample. The program combines mechanical testing, image processing, and data collection subroutines into a single interface. The technique is compatible with sample geometries and fabrication processes described in ASTM D5528, and it requires only the addition of a charge-coupled device (CCD) and light source. Compared with the manual techniques outlined in the ASTM standard, the introduced method provides enhanced resolution and reduced workload to determine crack length and resulting G_Ic of continuous glass fiber-reinforced composite DCB samples.