Fundamental Study on the Nondestructive Testing for Evaluating the Strength of Adhesive Wood Joints —Propagation Time of Sound Waves—

In order to develop a nondestructive testing method applicable to manufacture more reliable adhesive wood components, fundamental experiments were performed. The strength of adhesive wood joints was evaluated by measuring the time of sound waves (stress waves, ultrasonics) propagating the part involving adhesive joints to guarantee the bonding strength more directly. The three types of experiments employed were as follows: (1) Measuring the propagation time of stress waves for the end joint and lap joint specimens in the curing process. (2) Measuring the propagation time of sound waves for the end joint specimens before and after gluing. (3) Mesuring the propagation time of ultrasonics in both thickness and width directions and the adhesive shear strength for the two-layer specimens. The results are summarized as follows: (1) Curing of adhesive joints could be evaluated by the propagation time of stress waves. (2) The change of propagation time before and after gluing indicates the difference in the state of adhesive joints. (3) The propagation time of ultrasonics in the thickness direction was effective for evaluating the shear strength of adhesive joints, but that in the width direction was not so effective. However, the shear strength can be evaluated more effective by combining the propagation time in these two directions.