Search

The ultrasonic wave velocities in wood impregnated with a fire-retardant chemical were measured via a non-contact method. An air-coupled ultrasonic wave was made to propagate along the radial direction of the wood. The wave velocities in the wood samples after chemical impregnation were larger than those before impregnation. With increased chemical concentration, the relative changes in the velocities increased to a maximum of 16.3%, and these velocity changes exhibited a strong correlation with the chemical retention. These findings suggest that it is possible to evaluate the uniformity distributions of chemicals in fire-retardant-treated wood via a non-contact and nondestructive method based on air-coupled ultrasonics.

A study is made on the effect of delamination on the natural vibration characteristics of laminated beams. Free vibration of the simply supported beam with a delamination of arbitrary size and location is analyzed on the basis of the Euler beam theory. Axial forces induced by bending in the parts of the beam above and below the delamination are determined by regarding the cracked part as two lapped beams hinged at both ends. Numerical results for natural frequencies, mode shapes and normal contact pressure between the delaminated layers are presented for the first four modes. Experiments are also conducted. It is shown that the analytical solutions for natural frequencies agree well with experimental results.