ACOUSTIC EMISSIONS FROM PLYWOOD IN SHEAR BY TENSION LOADING

Plywood specimens (three-ply), made under several conditions of the gl ue spread of urea-formaldehyde resin and open-assembly times, were tes ted in shear by tension loadings while being monitored for acoustic em issions (AEs). The mechanism of AE generation was examined through the location of the AE source across the thickness of the specimens and t he attenuation of the AE waves during propagation. AE activities were greater in the region that included the face and back plies and the gl ue lines than in the central zone of the cores of specimens cut both f or lathe checks to pull closed and to open. The regions of great AE ac tivity, however, were not consistent necessarily with the actual occur rences of failures. It was found from an amplitude analysis that AEs f rom a core had greater amplitudes and those from the region near the g lue-line lesser amplitudes, particularly for specimens of great bond s trengths cut for lathe checks to pull closed. In addition, for specime ns cut for lathe checks to pull closed, there were good relationships between attenuation constants for AE waves to propagate through specim ens and bond strengths.