Contribution to the study of the nondestructive evaluation of timber using ultrasonic technique

Author(s)

Fabiana Goia Rosa de Oliveira

• Document type: Doctoral Thesis
• Press: São Carlos.
• Institution: Universidade de São Paulo (USP). Instituto de Física de São Carlos (IFSC/BT)
• Defense date: 2005-06-20

Examining board members

Almir Sales; Carlito Calil Junior; Mauro Augusto Demarzo; Antonio Alves Dias; Francisco Antonio Romero Gesualdo

• Advisor: Almir Sales

Abstract

The aim of this research was to evaluate the influence of moisture content and dimensions of specimens on the ultrasonic velocity in wood. The species used were: cupiúba (Goupia glabra),eucalipto grandis (Eucalyptus grandis), jatobá (Hymenaea spp), eucalipto citriodora (Eucalyptus citriodora), pinus caribea (Pinus caribea var. caribea) and pinus elliottii (pinus elliottii var. elliottii). Ultrasonic measurements were taken with the experimental equipment Sylvatest with 22 kHz transducers. Experimental procedure about dimensions were carried out in two steps: specimens of constant length and variable cross−section and of constant cross−section and variable length. In the first case, were taken twelve specimens with initial cross−section of 6 cm x 12 cm, planed until 1 cm x 12 cm and constant length (50 cm). In the second case, were taken twelve specimens with length from 300 cm to 10 cm and constant cross−section (6 cm x 12 cm). Ultrasonic measurements were made in the longitudinal direction. They were also made destructive tests in beams and specimens with the purpose of comparison between static and ultrasonic methods. In the study of the influence of moisture content, twelve specimens (2.5 cm x 30 cm x 75 cm) were dried from green until about 6% moisture content The results showed that the influence of cross−section depends on the relation between dimensions and wavelength, when λ is next to one of the dimensions, the ultrasonic velocity decreases because edge’ s effect. The study about the length showed that there is a critical point in the relation between sample length and wavelength (L/λ), and above it the velocity is not affected. The results about moisture content demonstrated that ultrasonic velocity, parallel and perpendicular to the grain, decreased when moisture content increased, and this influence was more significant below the fiber saturation point. It was developed an expression to correct the ultrasonic velocity as a function of moisture content and density of wood (AU)