Through-thickness ultrasonic characterization of wood and agricultural fiber composites

Direct contact ultrasonic transmission (UT) method was used to differentiate the effects of particle size on panel properties for oriented strandboard (OSB), redcedar particleboard (RCPB), and bagasse particleboard (BAPB). The measurements were done after conditioning samples at 50 and 70 percent relative humidity (RH) at 24 degrees C. It was found that the equilibrium moisture content (EMC) was positively related to particulate size of the respective panel types. The UT variables attenuation and root mean square voltage values varied significantly at the two EMC levels for the single-layer RCPB. Internal bond (IB) strength of a test panel type was affected by processing factors such as layering, resin content, and type of resin. The inclusion of bark in the RCPB panel had an adverse effect on IB. Ultrasonic velocity was found to be a good indicator of physical particle impediment to the propagation of stress waves in OSB and RCPB panels, but not in BAPB panels. The variable impedance was shown to be a reliable measure of tortuosity of velocity flux through the material. Minimum attenuation and maximum RMS points for RCPB, OSB, and BAPB were obtained at approximate density values 0.75, 0.9, and 1.1 g/cm3, respectively, marking the respective minimum void scattering and absorption in each panel type. For the respective panel types, the greatest transmissivity of stress wave energy occurred at these density values (the zero void densities). Beyond these densities, absolute IB appeared to diminish with density. Hence, an appropriate ultrasonic system calibration of these material factors is essential for optimizing the desired properties of these reconstituted composites in the production line.