Nondestructive assessment of glued joints in timber applying vibration-based methods

In this study, three different shapes and glue coverage rates of joints were evaluated ‎nondestructively using longitudinal and flexural vibration-based methods. Rectangular specimens ‎of 20‎‏×‏‎40‎‏×‏‎360 mm (R‎‏×‏T‏×‏L) dimensions were prepared from clear eastern beech (Fagus ‎orientalis; Lipsky) woods. Joints were located at the middle of the beams. The selected joint ‎shapes were 45o scarf joint, 30o scarf joint and finger joint with 10 mm length and 3mm pitch. ‎Longitudinal vibration test proved a better assessment for gluing than flexural efficiency. Some ‎weaker jointed timbers could demonstrate identical Young's moduli by both longitudinal and ‎flexural vibration-based methods. In the presence of any significant difference between Young's ‎moduli evaluated by two methods, it was realized that the joints were weak and required to be ‎rejected or assigned for re-manufacturing. The R2 of Timoshenko's linear model significantly ‎decreased when there was any un-integrity in the joints. This factor was suggested be used as a ‎potential subsidiary indicator. The vibration-based methods were recommended to be applied for ‎joint assessment of the old jointed timbers and for grading newly constructed jointed lumbers.‎

Assessment/ Beech/ Glue/ Joint/ Lumber / Nondestructive/ Timoshenko/ Vibration