Yoshiyasu Fujimoto

Behavior of acoustic emission generation during tensile tests perpendicular to the plane of particleboard II: Effects of particle sizes and moisture content of boards

Particleboard specimens with various particle sizes were conditioned into two ranges: low and high moisture content. One set was investigated for internal bond (IB) strength and acoustic emission (AE) events during tensile tests perpendicular to the plane and the other for ultrasonic wave transmission characteristics in the thickness direction. The particleboard structural mechanics were changed as a result of the moisture effect. Specimens conditioning to higher moisture content had lower IB strength and lower cumulative acoustic emission event counts (TAE). The decrease in IB strength indicated that the irreversible thickness swelling was seen when recovery forces of the particles exceed the restraining action of the adhesive. This was attributed to stress release, which resulted in internal failure of the board. The change in the internal structure caused an increased stress level at the initiation of AE generation. No events were recorded before this stress level, obeying theKaiser effect. The decrease inTAE was not only related to the decrease in IB strength but was also affected by the transformation (attenuation) of the AE signals during IB tests according to the mesh size used.