Wood plastic plywood (WPPW), composed of veneer and styrofoam, was manufactured without special adhesives such as urea-formaldehyde or phenol-formaldehyde resins, and its vibrational properties were investigated. WPPW can be produced at 1MPa and 160°C for 9 min (three-ply) and 12 min (five-ply). The dynamic Young's modulus reached its highest value when the styrofoam thickness was 30 mm. The sound velocity and dynamic Young's modulus had minimum values at a grain angle of 45°. The results for dynamic Young's moduli measured by a longitudinal vibration method and an in-plane flexural vibration method were almost the same. Dynamic shear moduli were measured by an in-plane surface wave propagation test and an in-plane flexural vibration method. From the experimental results, the dynamic shear moduli at 0° and 90° by the two methods were relatively close, although the surface wave propagation test results were higher than those from the flexural vibration method. Dynamic shear moduli at a grain angle of 45° measured by the in-plane surface wave propagation test and calculated from theory were relatively close. The surface wave propagation test results were smaller than the results calculated from theory. The shear stress distribution factors were about 1.000-1.189 for WPPW.
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