Title: Acoustic tomography in relation to 2D ultrasonic velocity and hardness mappings
Author: Li, Li; Wang, Xiping; Wang, Lihai; Allison, R. Bruce
Source: Proceedings of the 16th International Symposium on Nondestructive Testing and Evaluation of Wood, October 12-14, 2009, Beijing, China. Beijing, China : Beijing Forestry University, c2009: p. 28-35.
Description: Acoustic tomography is an emerging NDT technology for tree decay detection in both urban community and production forest. Many field studies have been conducted to assess the applicability and reliability of the technique in such applications. Although investigations on urban trees showed great success using acoustic tomography to detect moderate to severe internal decay within the trunk, detection of early stage of decay using such technology still constitutes a challenge This study was designed to evaluate the accuracy of acoustic tomography by analyzing the relationships between acoustic tomograms and two-dimensional mappings of ultrasonic properties and end hardness of the same trunk cross-sections. A freshly cut black cherry log was used to simulate a tree trunk and tested in the laboratory. Time-of-flight (TOF) acoustic tomography measurements were conducted at three different heights (10cm, 30cm, and 50 cm). A disc was then cut from each height and subjected to ultrasonic and mechanical evaluations. It was found that the acoustic shadows in the tomograms revealed internal structural defects that were at same locations and in similar magnitudes as the physical mappings of the discs. However, the shapes of the defect areas in the velocity and hardness mappings do not exactly match the acoustic shadows. Statistical analysis showed poor relationships between apparent velocity of the tomograms and measured ultrasonic velocity and end hardness. The acoustic tomograms obtained on the black cherry log represented a very narrow range of apparent velocity (COV=8.l-13.4%) in contrast to the wide range values for ultrasonic velocity (COV=33.8-37.3%) obtained from the discs. The results of this study suggest that TOF acoustic tomography has limited capability in detecting early stages of decay in trees.
Keywords: Nondestructive testing, tomography, acoustic imaging, deterioration, testing, hardness, acoustic properties, wood quality, wood defects, black cherry, wounds, injuries, evaluation, Prunus serotina, wood grading, ultrasonic testing, grading, trees, biodegradation, wood decay, acoustic testing, black cherry, heartwood, log grading, log quality
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Li, Li; Wang, Xiping; Wang, Lihai; Allison, R. Bruce; 2009. Acoustic tomography in relation to 2D ultrasonic velocity and hardness mappings. In: Proceedings of the 16th International Symposium on Nondestructive Testing and Evaluation of Wood, October 12-14, 2009, Beijing, China. Beijing, China : Beijing Forestry University, c2009: p. 28-35.
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