Résumé
Wood is an orthotropic material and its properties depend on its age but also depend on environmental growing conditions. An important feature of property alteration is reaction wood formation. Reaction wood forms when part of a tree is subjected to mechanical stress, and helps to bring parts of the plant into an optimal position. This article aims to study the effect of reaction wood on ultrasonic wave propagation using tomographic imaging. The ultrasonic emission was a pulse train of square wave. The peak frequency was 80 kHz. Two logs of poplar and spruce were tested because of the presence of different types of reaction wood (tension wood for poplar and compression wood for spruce). Maps were computed according to the Radon theory and using a filtered back projection algorithm with fan beam geometry. The intrinsic parameters were the slowness (s/m) and attenuation (dB/m at 80 kHz). In addition to ultrasonic tests, X-ray imaging in transmission was used. The ultrasonic maps were analyzed to highlight the differences between normal wood and observed reaction zones. The X-ray images were also compared to ultrasonic maps and the relationships between X-ray attenuation and ultrasonic parameters were discussed.