Ultrasonic techniques for nondestructive testing of standing trees

Abstract

The aim of this study is to assess wood quality of standing trees with ultrasonic velocity methods. The ultrasonic techniques currently used are: scattering based techniques that use travel time and other wave parameters for measuring the elastic constants of wood, and ultrasonic tomographic imaging techniques which seek to provide a high resolution picture of the defect. Scattering based techniques were firstly used as nondestructive techniques with increment cores of 5 mm diameter. On these specimens measurements with bulk waves––longitudinal and shear were used to detect the influence of sylvicultural treatment (pruning) on wood quality and also to detect defects (slope of grain, wavy figures). High resolution imaging techniques were developed for imaging abnormalities induced by biological attacks of fungi or insects in standing trees. In this case, ultrasonic tomography refers to cross-sectional imaging of trees from data collected by illuminating the tree from different directions. Ultrasonic images were reconstructed from the time of flight. The images were reconstructed from 120 measurements in situ and through the bark with direct transmission technique, using 1 MHz transducers. The resolution is 5 cm.