Projeto de desenvolvimento de um densitômetro de ultrassom para ensaios não destrutivos em madeira

Abstract

There are few effective techniques for determining the basic density of trees in the field. The non-destructive ultrasonic wave propagation test has the potential to predict the properties of wood, if the variables of this process are known. The objective of this research was to develop a densitometer to predict the basic density of wood, using the principle of propagation speed of ultrasonic waves. Two prototypes of the equipment were designed and assembled: a version without amplifier (Prototype I) and another amplified (Prototype II). The propagation speeds of the ultrasonic wave were determined, using the equipment prototypes, for six species of eucalyptus. The propagation of ultrasonic waves was carried out with the James V-Meter IV equipment to validate the densitometer. To estimate the basic density of wood, a mathematical modeling of the propagation of longitudinal waves was used. The model inputs were the longitudinal modulus of elasticity at static bending, the longitudinal-radial Poisson's ratio, and the ultrasonic wave propagation velocity. To evaluate the efficiency and effectiveness of the densitometer, the basic density obtained by the densitometer was compared with that obtained by the reference method of the hydrostatic balance. Prototype I underestimated the ultrasound propagation velocity in wood (3,947.21 m.s-1) and Prototype II made velocity measurements (4,751.55 m.s-1) in agreement with the reference ultrasound equipment that obtained the average value of 4,769.17 m.s-1. Prototype II using the three-dimensional modeling of wave propagation in wood was the one that obtained the best estimate of the basic density, with RMSE of 8.94% and bias of 1.66%, while Prototype I obtained the RMSE of 23.12 % and bias of 1.5%.