Structural mechanics of wood composite materials II: Ultrasonic propagation mechanism and internal bonding of particleboard

Abstract

Ultrasonic nondestructive evaluation (NDE) methods have been successfully applied for grading lumber and veneer at the in-plant level. To expand this application in wood composite production, further research is needed to elucidate the effect of differences of component elements within wood composite panels on the behavior of ultrasonic waves traveling through them. The objective of this study was to investigate the effects of the internal bonding of particleboard specimens containing component chips of different geometry on ultrasonic velocity. Commercial chips screened at four sizes were used to produce particleboard specimens with different internal bonding by controlling their out-of-press thickness at (a) a constant thickness for boards made of each chip size, and (b) four different thicknesses for boards made of the same chip size. Twenty-four boards were made with phenol-formaldehyde (PF) resin at 8% solid resin content in our laboratory. After the velocities of the waves traveling through the thickness of the boards were recorded, the internal bond strengths were tested. Results showed the density, internal bond state, and constituted chip geometry were the main factors influencing the velocity. NDE using ultrasonic waves is an available method to evaluate the internal bonding of particleboard with a density less than about 0.75 g/cm3. With densities over that value, no significant changes of the velocity were found. © The Japan Wood Research Society 1999.