Novel slanted incidence air-coupled ultrasound method for delamination assessment in individual bonding planes of structural multi-layered glued timber laminates.

摘要: Non-destructive assessment of delaminations in glued laminated timber structures is required during their full life cycle. A novel air-coupled ultrasound (ACU) method has been developed, which able to separately detect individual bonding planes arbitrarily high and long stacks typically 200 mm wide. The 120 kHz ACU transmitter–receiver pair positioned at two opposite lateral faces the sample, with a small inclination respect inspected planes, so that an beam excited user-defined refraction angle within interacting defects limited height portion stack. attenuation transmitted across defect (negative detection) provided better sensitivity than scattered fields (positive detection), are masked by spurious fields. Dedicated finite-difference time-domain (FDTD) simulations understanding on wave propagation detectability limits, heterogeneous anisotropic material structure introduced curvature annual rings lamellas. simplified analytical expression was derived calculate angles function insonification ring angle. Experimental results show >20% wide both isotropic glulam straight year rings, >50% 100 commercial beams. discrimination from background variability optimized normalizing images reference defect-free sample sections (normalization) or previous measurements (difference imaging), combining readings obtained distinct (spatial diversity). Future work aims development tomographic inspection described theoretical experimental methods.