Effects of cyclic loading on velocities of ultrasonic waves propagating through wood

The aim of this study was to determine the acoustoelastic phenomenon of wood under cyclic loading-unloading processes. Compression or tension load was repeatedly applied to wood specimens within an elastic range. Ultrasonic waves used in this study were shear and longitudinal waves, and their propagation directions were normal to, and along, the loading directions. The ultrasonic wave velocities were obtained by the sing-around method, which is a method for measuring transit time of ultrasonics. The experimental results revealed that change in the velocity of ultrasonic waves passing through wood under axial stress was a nearly linear function of applied stress level with similar slope for both loading and unloading cycles. The acoustoelastic effect of wood was found to be a repeatable and reversible phenomenon. The acoustoelastic constant seemed to maintain a fixed value regardless of the number of loading cycles. The acoustoelastic technique could be used in the determination of stress conditions of structural components in timber construction.