Marcela Candian

Moisture content effect on ultrasonic velocity in Goupia glabra

This paper discusses the application of ultrasound waves on a Brazilian hardwood, Goupia glabra, to evaluate the sensitivity of the ultrasonic technique to the moisture content in wood. The velocity of ultrasonic wave is sensitive to the materials quality-determining factors; hence, this technique is an important industrial tool to improve the quality control of processes. The nature of the response of velocity of sound to changes in moisture content led us to conclude that moisture gradients during drying exert a dominating effect. The ultrasonic velocity was measured both parallel and perpendicular to the fibers of Goupia glabra during drying from green to 6% moisture content. The results of this study showed that velocity of ultrasonic waves is sensitive to changes in moisture content of lumber during drying. The velocity under dry conditions was always higher than the velocity under more humid conditions, in both directions of propagation.

Efeito do comprimento do corpo-de-prova na velocidade ultra-sônica em madeiras

This paper reports on a study of the variation of ultrasonic velocity with the length of the specimen of pinus caribaea (Pinus caribaea var. caribaea) eucalipto citriodora (Eucalyptus citriodora), eucalipto grandis (Eucalyptus grandis) and jatoba (Hymenaea sp). Ultrasonic measurements were taken with an experimental apparatus having 22 kHz transducers. Tests were carried out with length from 300 cm to 10 cm and constant cross-section (12 cm x 5 cm). The results showed that velocity of ultrasonic waves is sensitive to changes in the distance between transducers and wavelength ( λ). The adjustment between the frequency of transducer and the length of the specimen is essential in order to obtain correct measurements of ultrasonic velocity in wood.