Ultrasonic Characterization of Different Wood Samples

Abstract

Wood is a natural raw material having both orthotropic anisotropy and its variability. Wood is a biological material integrating a very large variability of its physical and mechanical properties. The variability is strongly dependent on the direction of grains and other quality parameters like velocity, density etc. Physical appearance of the variability is due to ring average width and density of wood. For industrial applications, like structural applications or timber construction, the micro-structural basic variability associated to a macroscopical variability induced by singularities like knots, cracks, local decay or even local dynamic compression failure. To improve the wood quality grading in several steps of the industrial wood transformation, ultrasonic characterization readings would be useful. In first experimental study, Eight different wood samples like Acacia auriculaeformis (Bengaljali), Eucalyptus tereticornis (Eucalypts) Heveabrasiliensis (Rubber wood), Mangiferaindica (Mango), Melia composite (Malabar neem), Radiata pine (Pine) and Shorearobusta (Sal) were computed for ultrasonic parameters like velocity, specific gravity, acoustic impedance, adiabatic compressibility and modulus of elasticity at different frequencies of 1MHz, 2.25MHz and 3.25MHz. Ultrasonic velocity, adiabatic compressibility, acoustic impedance, modulus of elasticity, modulus of rupture, and maximum crushing stress parallel to grain were found varying between 1000 m/s to 1667 m/s, 0.180 x 10-6 to 0.67 x 10-6 Pa-1 , 1400 to 3334 N-s/m2, 437 to 1066 kg/m2, 200 to 599 kg/m2 respectively. The results of the study will be helpful to characterize the different wooden samples. Moreover, properties of different samples can be expressed by their acoustical behaviour. In second experimental study five different wood samples like Acacia auriculaeformis (Bengaljali), Eucalyptus tereticornis (Eucalypts), Melia composite (Malabar neem), Shorearobusta (Sal) and Teak were used for study. Non-destructive technique (NDT) was employed for study the physical parameters and Scanning electron microscopy (SEM) was employed to capture image from the surface of the wood in longitudinal and transverse direction. These images were used to study the wood fibrous structure in different pattern 20 to 120 μm, pores size (vessel element) 50 to 400 μm, fiber size 5 to 30 μm and compare with ultrasonic physical parameters like ultrasonic velocity, acoustic impedance and elasticity along the grain were found varying between 3466 m/s to 4929 m/s, 0.699 x 10-6 to 2.92 x 10-6 N-s/m2, 2.89 x 10-9 to 12.58 x 10-9 Pa and in transverse direction 1733.33 m/s to 2571.42 m/s, 0.292 x 10-6 to 1.209 x 10-6 N-s/m2, 0.507 x 10-9 to 2.99 x 10-9 Pa respectively. The aim of this study was to understand the ultrasonic behaviour in different wood structure. The results of the study will be helpful to characterize the different wooden samples. 4