A Study On Dynamic Properties Of Wood-based Composites

In order to investigate the dynamic properties of wood-based composites, sound velocities, dynamic Young's moduli and dynamic shear moduli of wood-plastic (WP), wood-fiberboard (WF), wood-metal (WM) composite, wood plastic plywood (WPPW), veneer-overlaid particleboard (VOP) and veneer-overlaid MDF (VOM) were measured by longitudinal transmission, longitudinal vibration, flexural vibration, surface wave propagation test.For WP, WF and WM, the effects of grain angles of face veneer on sound velocities, dynamic Young's moduli, and shear moduli were investigated. The effects of wood element on properties of wood-based composites were analyzed. The possibility that sound velocities, dynamic Young's moduli and shear moduli of wood-based composites can be predicted by means of some empirical formula was also discussed. For WPPW, the effect of thickness of styrofoam on the dynamic Young's modulus of WPPW was investigated. The surface wave propagation method was proposed to measure the dynamic shear moduli of WPPW to solve the problem for measurement of dynamic shear moduli of WPPW at 45?grain angle. For VOP and VOM, the effects of veneer thickness, grain angle and shelling ratio on dynamic Young's moduli were investigated. The possibility that dynamic Young's moduli of veneer-overlaid wood-based panels can be predicted by means of empirical formula was also discussed.The results were summarized as follows:(1) Grain angles of face veneer have significant effects on sound velocities and dynamic Young's moduli of WP, WF, WM and WPPW. For WP, WF and WM, in the range of 0°~90°, the sound velocities and dynamic Young's moduli decreased with increasing the grain angles. However, for WPPW, the sound velocities and dynamic Young's moduli decreased with increases of grain angles from 0° to 45°. On the other hand, the sound velocities and dynamic Young's moduli increased with increases of grain angles from 45° to 90°. The minimum values of sound velocity and dynamic Young's modulus were found at the grain angle of 45°.(2) When the orthotropic properties of wood and wood-based composites were considered as the values of V0/V90, they were 5.1 for wood and 4.7, 3.8, 1.5 for WP, WF,and WM respectively. The relationship between grain angle of face veneer and sound velocity of three types of wood-based composites can be expressed in the form of Hankinson's equation or a second order parabolic equation.(3) For WPPW (the thickness of styrofoam was 10mm before hot pressing), sound velocity of WPPW at the 0° grain angle of face veneer was approximately two times as much as that of WPPW at the 45° grain angle of face veneer. On the other hand, sound velocity of WPPW at the 45° grain angle of face veneer was approximately 60% of that at the 90° grain angle.(4) When the orthotropic properties of wood and wood-based composites were considered as the values of E0/E90, they were 25.7 for wood and 24.5, 15.8, 2.4 for WP, WF and WM respectively. The relationship between grain angle of face veneer and Young's modulus of three types of wood-based composites could be expressed in the form of Jenkin's equation, Hankinson's equation, or a second order parabolic equation.(5) For WPPW, dynamic Young's modulus at the 0° grain angle of face veneer was approximately 6~7 times as much as that at the 45° grain angle of face veneer; dynamic Young's modulus at the 0° grain angle of face veneer were approximately 1.6-2 times as much as that at the 90° grain angle. The results of dynamic Young's moduli measured by longitudinal vibration method and in-plane flexural vibration method were almost the same. The dynamic Young's modulus reached the largest value when the thickness of styrofoam was 30mm in this study.(6) Grain angles of face veneer have significant effects on dynamic shear moduli of three types of wood-based composites. The dynamic shear moduli decreased with increasing the grain angles. When the orthotropic properties of wood and wood-based composites were considered as the values of G0/G90, the...