Nondestructive evaluation of strength performance for finger-jointed wood using flexural vibration techniques

This paper deals with flexural vibration techniques as a means of predicting modulus of rupture (MOR) and static modulus of elasticity (MOE) of finger-jointed wood specimens made with Sitka spruce (Picea sitchensis Carr.) and red pine (Pinus densiflora S. et Z.). Dynamic MOE was calculated from resonance frequencies obtained from forced vibrations induced in the two species of finger-jointed wood specimens by a magnetic driver and a tapping hammer. The dynamic MOE was well correlated to the static bending MOE and its value also showed a reasonable correlation with bending MOR, although the correlation coefficient was lower than that between the dynamic MOE and static bending MOE. It was found that the correlation of the dynamic MOE to MOR was higher in the magnetic driver with both ends free condition than in the tapping hammer condition. For both methods, red pine finger-jointed wood specimens showed higher correlation coefficients to the MOR than Sitka spruce finger-jointed wood specimens. The correlation coefficient values for the magnetic driver and tapping hammer methods were almost equal to or slightly lower than those for static MOE and MOR for red pine and Sitka spruce finger-jointed wood specimens. It can be concluded that the two flexural vibration techniques are useful for predicting the MOR and static MOE of finger-jointed wood specimens.