Evaluation of some influential factors in the ultrasonic velocity in the wood

Abstract

. Ultrasound has been used for detection of defects in different homogeneous materials since the 1970s. In wood, as a heterogeneous material, its use is recent in Brazil. Ultrasonic wave propagation is influenced by several factors such as the forest species, type of transducer and environmental temperature. Aiming at studying the influence of such factors, this research involved the use of point-contact transducers. Wood of two different species (Pinus elliottii Engelm. and Eucalyptus grandis Hill ex Maiden) were dried at constant temperatures of 20, 40, and 70ºC. The models proposed for analysis showed significant influence of moisture content, specific mass and drying temperatures on ultrasonic velocity. Increase of velocity occurred due to a reduction of moisture content, over the range of green wood to the end of the drying process. Eucalyptus had the best results, with a determination coefficient of 71%. The increase of ultrasonic velocity was directly proportional to the specific mass on pine wood; but inversely proportional to that for eucalyptus one. The ultrasonic velocity also showed a tendency to decrease with the increase of drying temperature. In spite of the existence of specific transducers to be used in the wood, knowledge of the several characteristics of this material in the propagation of the ultrasonic waves is needed, mainly when the great diversity of remaining forest species in tropical countries is taken into account, as it is the case of Brazil.