Automated bondline thickness quantification in adhesively joined composites and metals using ultrasound

The use of adhesively bonded joints between composite panels, metal panels, or between composites and metals are used in the aerospace and automotive industries to avoid stress concentrations due to fasteners while reducing weight. Quantifying the bond thickness allows for confidence that loading is being properly transferred. This study presents a methodology to measure bondline thickness using the data obtained from an immersion quality ultrasound scan using an out‐of‐tank, field‐portable, utlrasonic testing (UT) scanner. Eighteen bonded coupons were fabricated using a paste‐type adhesive filling a range of gaps between substrates of 0.254 and 1.27 mm. Three adhesively bonded coupon types were investigated: carbon fiber laminates, fiber glass laminates, and aluminum plates. A semiautomated algorithm is presented to quantify bondline thickness from the ultrasound data for each coupon type, generating a spatially varying 3D point cloud of adhesive thickness. Bondline measurements obtained using ultrasound are then validated over two orthogonal planes against measurements taken from x‐ray computed tomography reconstructions. Results indicate a typical accuracy of 0.081 mm for bondline thickness quantification for all samples studied, with the results from the inspection of the composite coupons yielding an error of 0.078 mm, whereas the accuracy when scanning the aluminum coupons yielded an error of 0.086 mm.