Ultrasonic Characterization of Structural Properties of Oriented Strandboard: a Comparison of Direct-contact and Non-contact Methods1

A through-thickness ultrasonic transmission (UT) in oriented strandboard (OSB) was done to compare the performance of direct-contact (DC) and non-contact (NC) ultrasonic systems. The DC measurements produced a higher velocity than the NC system for a given board type, possibly due to transducer’s compression over liquid couplant in the DC method. The UT responses correlated nonlinearly to sample density. The responses were not affected by the panel shelling ratio for the threelayer boards. Viable correlations between panel properties and UT parameters were board-specific for either method. Attenuation and root means square voltage (RMS) parameters were suitably used as density predictors if the flake alignment level is known; otherwise, velocity parameter could be used. In the single-layer boards, internal bond strength, bending stiffness, and breaking resistance were highly correlated to attenuation and RMS, a calibration importance. A density of 900 kg/m3 marked the transition point for the UT responses. The point showed the transition between the diminishing physical effects of the interspatial voids in the lower density half and the increasing plastic-strain hardening modifications in the higher density half. The high correlations of DC-Velocity and NCAttenuation to density and strength properties attest a feasible application of both methods in wood composite research and in a real-time quality control system for fiber-based facilities.