An examination of the feasibility of using time-of-flight based non-destructive evaluation to assess the soundness of standing Acacia koa
In: Proceedings of the 3rd international scientific conference on hardwood processing; 2011 Oct. 16-18; Blackburg, VA. Blacksburg, VA: Virginia Polytechnic Institute and State University: 273-280.
Koa (Acacia koa) trees are native to the islands of Hawaii but occur nowhere else in the world. It is the most important timber species for the manufacture of wood products in Hawaii and one of the most valuable species worldwide. Most koa trees harvested today are standing dead or are already on the ground (relic logs). Lumber recovery in milling koa is very low - about 20% of the koa log is recovered as lumber. Wounds, broken out limbs, and branch crotches provide visual indication of the likely existence of decay inside the koa tree, but the extent of this decay is highly variable and difficult to predict. The challenge for timber sellers and buyers is to form a reasonable estimation of the degree of decay and the volume of the log that is affected. One tool that has had some success in predicting wood quality, measures the time-of-flight (TOF) of stress waves and may offer insights into the trees' decay. The objective of this preliminary study was to evaluate the relationship between TOF stress-wave data and corresponding decay observations to determine the feasibility of using this technology on koa. TOF data was collected at three heights and in two directions per height on eight standing koa trees at a single harvest site on the Island of Hawaii. TOF data also was collected from the butt logs of these trees after felling. The variability in the TOF results was large among trees, ranging from 246 to 2092 meters per second. The correlation between tree TOF and butt log TOF and lumber recovery was high. The correlation between tree TOF and the visible decay area on the large end of the butt log also was significant. Tree TOF and small-end decay area for the butt log were not significantly correlated. The feasibility of using TOF to predict the value potential of the lumber sawn from the butt log of a koa tree is uncertain - while lumber volume recovery was correlated with TOF, the decay proportions of the lumber products recovered were not found to be correlated. The lack of correlation between TOF and lumber soundness may be the result of the technique used in mapping the quality characteristics of the lumber where only one side of each piece was diagrammed due to time constraints. To produce quality lumber from these logs, the sawing pattern may have excluded any decay areas, thus resulting in lower volume recovery, which was correlated with TOF.
Wiedenbeck, Jan; Lowell, Eini. 2011. An examination of the feasibility of using time-of-flight based non-destructive evaluation to assess the soundness of standing Acacia koa. In: Proceedings of the 3rd international scientific conference on hardwood processing; 2011 Oct. 16-18; Blackburg, VA. Blacksburg, VA: Virginia Polytechnic Institute and State University: 273-280.